Chapter 3 Chemical Compounds

Transcription

1 Chapter 3 Chemical Compounds 3.1 (a) formula unit; (b) strong electrolyte; (c) molecular compound; (d) acid; (e) nonelectrolyte; (f) oxoanion 3.2 (a) molecular formula; (b) weak electrolyte; (c) ionic compound; (d) base; (e) binary compound; (f) polyatomic ion 3.3 Ionic compounds usually consist of a combination of metals and nonmetals. If the substance is composed of two or more nonmetals, it is usually molecular. For example, we identify the first two substances, K 2 S and Na 2 SO 4, as ionic because K and Na are both metals. In SO 2, both sulfur and oxygen are nonmetals, so SO 2 is molecular. 3.4 Ionic compounds usually consist of a combination of metals and nonmetals. If the substance is composed of two or more nonmetals, it is usually molecular. For example, we identify the first two substances, Na 3 N and KNO 3, as ionic because Na and K are both metals. In NO 2, both nitrogen and oxygen are nonmetals, so NO 2 is molecular. 3.5 Whether a molecular or ionic compound is formed can usually be determined by classifying the elements involved as metals or nonmetals. Metals generally combine with nonmetals to form ionic compounds and when two or more nonmetals combine they usually produce molecular compounds. Molecular compounds would be formed from (a) and (c) because the elements involved are nonmetals. Ionic compounds would be formed from (b) and (d) because potassium (K) and magnesium (Mg) are metals and each is paired with a nonmetal (O and Cl). If you are having trouble identifying metals and nonmetals, refer to Figure Whether a molecular or ionic compound is formed can usually be determined by classifying the elements involved as metals or nonmetals. Metals generally combine with nonmetals to form ionic compounds when two or more nonmetals combine they usually produce molecular compounds. Molecular compounds would be formed from (a) and (b) because the elements involved are nonmetals. Ionic compounds would be formed from (c) and (d) because calcium (Ca) and sodium (Na) are metals and each is paired with a nonmetal (Cl and N). If you are having trouble identifying metals and nonmetals, refer to Figure Both (a) and (d) would be molecular since both elements involved are nonmetals. Both (b) and (c) are ionic because of the presence of metals (Li and Ba) and nonmetals (F and Cl). 3.8 Only (b) is molecular because both elements (P and O) are nonmetals. The presence of the metals Al, Mg, and K coupled with S, Br, and O in (a), (c), and (d) indicate that those substances are ionic. 3.9 The attraction between oppositely charged ions is very strong. As a result, the ionic compound LiF would be expected to have the highest melting point. The attraction between molecules in molecular compounds is generally much weaker and thus CO 2 and N 2 O 5 would be expected to have lower melting points The attraction between molecules in molecular compounds is generally much weaker than the attraction between ions in ionic compounds. Therefore molecular compounds usually have lower melting points than ionic compounds. Of the three choices, CO is the only molecular compound and would be expected to have the lowest melting point of the three substances The position of an element on the periodic table can be used to predict the charges of monatomic ions. All three elements given are in Group 1A (1) and are expected to form 1+ ions. This gives them the same number of electrons as the nearest noble gas. (a) Na +, sodium ion; (b) K +, potassium ion; (c) Rb +, rubidium ion 3.12 The position of an element on the periodic table can be used to predict the charges of monatomic ions. All three elements given are in Group VIIA (17) and are expected to form 1 ions. This gives them the same number of electrons as the nearest noble gas. The names of monatomic anion names are based on the root of the element name plus the suffix ide. (a) F, fluoride ion; (b) Cl, chloride ion; (c) I, iodide ion 3-1

2 3.13 The charge of an ion can be predicted by the position of the element on the periodic table. Metals lose electrons to match the number of electrons in the nearest noble gas and nonmetals gain electrons to match the number of electrons in the nearest noble gas. Don t forget that as metals lose electrons, their charge becomes more positive because the electron carries a negative charge. (a) Ca 2+, calcium ion; (b) N 3, nitride ion; (c) S 2, sulfide ion 3.14 The charge of an ion can be predicted by the position of the element on the periodic table. Metals lose electrons to match the number of electrons in the nearest noble gas and nonmetals gain electrons to match the number of electrons in the nearest noble gas. Don t forget that as metals lose electrons, their charge becomes more positive because the electron carries a negative charge. (a) Al 3+, aluminum ion; (b) Ba 2+, barium ion; (c) P 3, phosphide ion 3.15 Table 3.4 lists the important polyatomic ions used in this chapter. From the image you should determine that there is one nitrogen (blue) and two oxygen atoms (red). Given that the charge is 1 and the formula is NO 2, the ion is the nitrite ion Table 3.4 lists the important polyatomic ions used in this chapter. From the image you should determine that there is one nitrogen (blue) and three oxygen atoms (red). Given that the charge is 1 and the formula is NO 3, the ion is the nitrate ion Table 3.4 lists the important polyatomic ions used in this chapter and Figure 3.17 can be used to quickly look up polyatomic oxoanions. (a) sulfate ion; (b) hydroxide ion; (c) perchlorate ion 3.18 Table 3.4 lists the important polyatomic ions used in this chapter and Figure 3.17 can be used to quickly look up polyatomic oxoanions. (a) sulfite ion; (b) cyanide ion; (c) chlorite ion 3.19 The polyatomic and monatomic ions are listed in Figure 3.17 and Table 3.4. (a) N 3 ; (b) NO 3 ; (c) NO The polyatomic and monatomic ions are listed in Figure 3.17 and Table 3.4. (a) ClO 2 ; (b) Cl ; (c) ClO The polyatomic and monatomic ions are listed in Figure 3.17 and Table 3.4. (a) CO 3 2 ; (b) NH 4 + ; (c) OH ; (d) MnO The polyatomic and monatomic ions are listed in Figure 3.17 and Table 3.4. (a) HCO 3 ; (b) CH 3 CO 2 ; (c) IO 4 ; (d) ClO 3.23 Table 3.4 lists the important polyatomic ions used in this chapter. From the image you should determine that there is one sulfur (yellow) and three oxygen atoms (red). Given that the charge is 2 and the formula is SO 3 2, the ion is the sulfite ion Table 3.4 lists the important polyatomic ions used in this chapter. From the image you should determine that there is one nitrogen (blue) and three oxygen atoms (red). Given that the charge is 1 and the formula is NO 3, the ion is the nitrate ion IO SeO A solution is electrically neutral. This means that the sum of the positive charges is equal to the sum of the negative charges. If there are five Al 3+ ions, representing a total positive charge of 15+, an electrically neutral solution would have 15 Cl ions (larger spheres) to balance the 15+ charge. 3-2

3 Cl Al A solution is electrically neutral. This means that the sum of the positive charges is equal to the sum of the negative charges. If there are five Mg 2+ ions representing a total positive charge of 10+, an electrically neutral solution would have 10 NO 3 ions to balance the 10+ charge. NO 3 Mg Compounds are electrically neutral. Here are two simple rules to follow: If the ions have the same charge, you only need one of each ion. If the charges are different, you can determine the chemical formula by considering what combinations of ions produces equal amounts of positive and negative charges. This can typically be accomplished by crossing the charges. If there is only one atom of an element, the number 1 is omitted in the chemical formula. Ba 2+ + Cl BaCl (a) BaCl 2 ; (b) FeBr 3 ; (c) Ca 3 (PO 4 ) 2 ; (d) Cr 2 (SO 4 ) Compounds are electrically neutral. Here are two simple rules to follow: If the ions have the same charge, you only need one of each ion. If the charges are different, you can determine the chemical formula by considering what combinations of ions produces equal amounts of positive and negative charges. This can typically be accomplished by crossing the charges. If there is only one atom of an element, the number 1 is omitted in the chemical formula. Na + + N 3 Na 3 N 1 3 (a) Na 3 N; (b) CsClO 3 ; (c) Ti 2 (CO 3 ) 3 ; (d) (NH 4 ) 2 S 3-3

4 3.31 Ionic compounds are made up of cations and anions. The cation is always written first. Usually the cation is a monatomic metal ion. The common exceptions are Hg 2 2+ and NH 4 +. The anion is either polyatomic or monatomic. (a) KBr Potassium and bromide ions are both monatomic and their charges are determined by their positions on the periodic table (see Figure 3.12). The ions in potassium bromide are K + and Br. (b) BaCl 2 Barium and chloride ions are both monatomic and their charges are determined by their positions on the periodic table. The ions in barium chloride are Ba 2+ and Cl. A common error is to assume that the chloride ion is Cl 2. Barium chloride is a combination of one Ba 2+ for every two Cl. (c) Mg 3 (PO 4 ) 2 Magnesium ion is monatomic and phosphate ion is polyatomic. Magnesium ion s charge is determined by its position on the periodic table. The charges of polyatomic ions can be found in Figure 3.17 and Table 3.4. The ions in magnesium phosphate are Mg 2+ and PO 4 3. (d) Co(NO 3 ) 2 Cobalt ion is monatomic, but it can have several different charges. To identify the charge of cobalt ion, you need to figure out the total negative charge. Nitrate ion is a polyatomic ion with a charge of 1. Since there are two nitrate ions, the total negative charge is 2. Since all compounds are neutral (zero net charge) the charge on cobalt ion must be 2+. The ions in cobalt(ii) nitrate are Co 2+ and NO 3. Mathematically we can summarize the charge of any ion or compound as: Total positive charge + total negative charge = overall charge In the case of this compound we can write Charge from cobalt + charge from the sum of all nitrate ions = 0 Co + 2 = 0 Cobalt ion s charge must be Ionic compounds are made up of cations and anions. The cation is always written first. Usually the cation is a monatomic metal ion. The common exceptions are Hg 2 2+ and NH 4 +. The anion is either polyatomic or monatomic. (a) NaBr Sodium and bromide ions are monatomic and their charges are determined by their positions on the periodic table (See Figure 3.12). The ions in sodium bromide are Na + and Br. (b) AlCl 3 Aluminum and chloride are monatomic ions and their charges are determined by their positions on the periodic table. The ions in aluminum chloride are Al 3+ and Cl. (c) Ba 3 (PO 4 ) 2 Barium ion is monatomic and phosphate ion is polyatomic. Barium ion s charge is determined by its position on the periodic table. The charges of polyatomic ions can be found in Figure 3.17 and Table The ions in barium phosphate are Ba 2+ and PO 4 3. (d) Mn(NO 3 ) 2 Manganese ions are monatomic, but they can have several different charges. To identify the charge of the manganese ion, you need to figure out the total negative charge. Nitrate ions are polyatomic with a charge of 1. Since there are two nitrate ions in the formula, the total negative charge is 2. Since all compounds are neutral (zero net charge), the charge on the manganese ion must be 2+. The ions in manganese(ii) nitrate are Mn 2+ and NO 3. Mathematically we can summarize the charge of any ion or compound as: Total positive charge + total negative charge = overall charge In the case of this compound we can write Charge from manganese + charge from the sum of all nitrate ions = 0 Mn + 2 = 0 Manganese ion s charge must be (a) Fe 2+ will form FeO. This balances the positive and negative charges. Fe 3+ will form Fe 2 O 3. If you have difficulty with this, you might consider crossing the charges as shown below. Notice that the least 3-4

5 common multiple for these two ions is 6. That is 2 3 = 6. This means that if you combine two Fe 3+ ions and three O 2 ions, the charge will balance to zero. This can be represented as follows: Fe 3+ O 2 + Fe 2 O (b) Since the charge on a chloride ion is 1, you need as many chloride ions as necessary to cancel the positive charge of the iron ions. Fe 2+ will form FeCl 2, and Fe 3+ will form FeCl (a) Cr 2+ will form CrO. This balances the positive and negative charges. Cr 3+ will form Cr 2 O 3. If you have difficulty with this, you might consider crossing the charges as shown below. Notice that the least common multiple for these two ions is 6. That is 2 3 = 6. This means that if you combine two Cr 3+ ions and three O 2 ions, the charge will balance to zero. This can be represented as follows: Cr 3+ O 2 + Cr 2 O (b) Since the charge of chloride ion is 1, you need as many chloride ions as necessary to cancel the positive charge of the chromium ions. Cr 2+ will form CrCl 2, and Cr 3+ will form CrCl (a) The overall charge is equal to the sum of the charges of the sodium ions and sulfate ions: Overall charge = (charge of sodium ions) + (charge of sulfate ion) = 0 Since the charge of the two sodium ions must balance the charge of sulfate, sulfate must have a 2 charge. (b) Since sulfate ion has a charge of 2, the charge of the strontium ion must be (a) The overall charge is equal to the sum of the charges of the magnesium ions and nitrate ions Overall charge = (charge of magnesium ion) + (charge of nitrate ions) = 0 Since magnesium ion has a charge of 2+, each nitrate ion must have a charge of 1. (b) Since nitrate ion has a charge of 1, the charge of potassium ion must be For each formula written, the charges do not balance so the compounds would have a net charge. In compounds, the sum of the positive and negative charges balance to zero (i.e. all compounds are neutral). (a) Sodium ion is Na + and chloride ion is Cl. In NaCl 2 there are too many chloride ions. Only one chloride ion is needed to balance the charge of the sodium ion. The correct formula is NaCl. (b) Potassium ion is K + and sulfate ion is SO 4 2. In the formula KSO 4 there are not enough potassium ions to balance the 2 charge on the sulfate ion. The correct formula is K 2 SO 4. (c) Aluminum ion has a charge of 3+ and nitrate ion has a charge of 1. In the formula Al 3 NO 3 there are not enough nitrate ions for the number of aluminum ions. Three nitrate ions are needed to balance the charge of one aluminum ion. The correct formula is Al(NO 3 ) For each formula written, the charges do not balance so the compounds would have a net charge. In compounds, the sum of the positive and negative charges balance to zero (i.e. all compounds are neutral). (a) Magnesium ion is Mg 2+ and chloride ion is Cl. In the formula MgCl there are not enough chloride ions to balance the 2+ charge of the magnesium ion. The correct formula is MgCl 2. (b) Sodium ion is Na + and sulfate ion is SO 4 2. In the formula Na(SO 4 ) 2 there are too many sulfate ions and not enough sodium ions. Two sodium ions are needed to balance the charge of one sulfate ion. The correct formula is Na 2 SO 4. (c) Potassium ion is K + and nitrate ion is NO 3. In the formula K 2 (NO 3 ) 2 the charge is balanced, but only one of each ion is necessary to balance the charge. The correct formula is KNO

6 3.39 To name these compounds we state the name of the cation followed by the name of the anion. It is important to note that prefixes such as di and tri are not often used in naming ionic compounds because the number of each ion can be determined from the charges of the ions. The cations in these compounds are all metals that have charges predictable from their position on the periodic table so it is not necessary to write the charges of the ions. (a) magnesium chloride; (b) aluminum oxide; (c) sodium sulfide; (c) potassium bromide; (e) sodium nitrate; (f) sodium perchlorate 3.40 To name these compounds we state the name of the cation followed by the name of the anion. It is important to note that prefixes such as di and tri are not often used in naming ionic compounds because the number of each ion can be determined from the charges of the ions. The metal cations in these compounds all have charges predictable from their position on the periodic table so it is not necessary to write the charges of the ions. (a) barium chloride; (b) ammonium sulfide; (c) magnesium oxide; (d) potassium nitrite; (e) magnesium phosphate; (f) potassium chlorite 3.41 Charges which cannot be predicted by the position of the element on the periodic table must be specified. Figure 3.12 shows many of the common ions (those metals which do not need their charges specified). Manganese, Mn, and cobalt, Co, compounds should have the charges specified with the metal name Charges which cannot be predicted by the position of the element on the periodic table must be specified. Figure 3.12 shows many of the common ions (those metals which do not need their charges specified). The charges of chromium, Cr, and nickel, Ni, should be specified in the name of the compound When the charge of the metal (cation) cannot be determined by its position on the periodic table, the charge is calculated from the chemical formula and the anion it is combined with. The charge can either be calculated [see part (a)] or deduced by inspection. This is possible because the charge of the anion is almost always predictable. (a) To calculate the charge we state that the total charge is equal to the sum of the positive and negative charges. Total charge = charge on copper + charge on oxygen 0 = 2 x + 2 Solving for x: 2x = 2 x = 1 The charge on the copper ion is 1+. To name the compound, write the name of the metal with its charge [i.e. copper(i)] followed by the name of the anion. The compound is named copper(i) oxide or cuprous oxide. (b) The charge on chloride ion is 1 and there are two chloride ions in the formula (a total of 2 charge from the anions). The charge on the chromium ion must be 2+ to balance the negative charge. The name of the compound is chromium(ii) chloride. (c) The charge on phosphate ion is 3. The charge of the iron ion must be 3+ to balance the negative charge. The name of the compound is iron(iii) phosphate or ferric phosphate. (d) The charge on sulfide ion is 2. The charge on the copper ion must be 2+ to balance the negative charge. The name of the compound is copper(ii) sulfide or cupric sulfide When the charge of the metal (cation) cannot be determined by its position on the periodic table, the charge is calculated from the chemical formula and the anion it is combined with. The charge can either be calculated [see part (c)] or deduced by inspection. This is possible because the charge of the anion is almost always predictable. (a) The charge on chloride ion is 1 and there are three chloride ions in the formula (a total of 3 charge). The charge on titanium ion must be 3+ to balance the negative charge. The name of the compound is specified by naming the metal with its charge (i.e. titanium(iii)) followed by the name of the anion. The name of the compound is titanium(iii) chloride. 3-6

7 (b) The charge on bromide ion is 1 and there are two bromide ions in the formula (a total of 2 charge). The charge on cobalt ion must be 2+ to balance the negative charge. The name of the compound is cobalt(ii) bromide. (c) To calculate the charge we state that the total charge is equal to the sum of the positive and negative charges. Total charge = charge on 2 Mn ions + charge on O 0 = 2 x + 3 (2 ) Solving for x: 2x = 6 x = 3 The charge on manganese ion is 3+. The name of the compound is manganese(iii) oxide. (d) The charge on phosphate ion is 3 and there are two phosphate ions in the formula (a total of 6 charge). Since there are three iron ions in the formula, the charge on each iron ion must be 2+ (to give a 6+ total charge). The name of the compound is iron(ii) phosphate or ferrous phosphate To write the chemical formulas of ionic compounds, first determine the formula for each ion and combine the ions so that the positive and negative charges balance. (a) Ca 2+ and SO 4 2 (one of each ion is needed) CaSO 4 (b) Ba 2+ and O 2 (one of each ion is needed) BaO (c) NH 4 + and SO 4 2 (two ammonium ions are needed to balance the charge of one sulfate ion) (NH 4 ) 2 SO 4 (d) Ba 2+ and CO 3 2 (one of each ion is needed) BaCO 3 (e) Na + and ClO 3 (one of each ion is needed) NaClO To write the chemical formulas of ionic compounds, first determine the formula for each ion and combine the ions so that the positive and negative charges balance. (a) K + and HCO 3 (one of each ion is needed) KHCO 3 (b) Na + and O 2 (two sodium ions are needed to balance the charge of one oxide ion) Na 2 O (c) NH 4 + and OH (one of each ion is needed) NH 4 OH (d) Mg 2+ and Br (two bromide ions are needed to balance the charge of one magnesium ion) MgBr 2 (e) Na + and ClO (one of each ion is needed) NaClO 3.47 The charge of the metal is determined from the formula and the charge of the anion. First determine the total negative charge contributed by the anions and then use that information to determine the charge of the metal ion. (a) The charge on chloride ion is 1 and there are two chloride ions in the formula (total charge 2). The charge on the cobalt ion must be 2+ (Co 2+ ). The compound name is cobalt(ii) chloride. (b) The charge on oxide ion is 2 and there are two oxide ions in the formula (total charge 4). The charge on the lead ion must be 4+ (Pb 4+ ). The compound name is lead(iv) oxide. (c) The charge on nitrate ion is 1 and there are three nitrate ions in the formula (total charge 3). The charge on the chromium ion must be 3+ (Cr 3+ ). The compound name is chromium(iii) nitrate. (d) The charge on sulfate ion is 2 and there are three sulfate ions in the formula (total charge 6). Since there are two iron ions, the charge on each iron ion must be 3+ (Fe 3+ ). The compound name is iron(iii) sulfate or ferric sulfate The charge of the metal is determined from the formula and the charge of the anion. First determine the total negative charge contributed by the anions and then use that information to determine the charge of the metal ion. (a) The charge on bromide ion is 1 and there are three bromide ions in the formula (total charge 3). The charge on the cobalt ion must be 3+ (Co 3+ ). The compound name is cobalt(iii) bromide. (b) The charge on chloride ion is 1 and there are two chloride ions in the formula (total charge 2). The charge on copper ion must be 2+. The compound name is copper(ii) chloride or cupric chloride. (c) The charge on oxide ion is 2 and there are three oxide ions in the formula (total charge 6). The total positive charge must be 6+ to balance the negative charge. The charge on each chromium ion must be 3+ (Cr 3+ ). The compound name is chromium(iii) oxide. 3-7

8 (d) The charge on sulfate ion is 2. The charge on iron ion must be 2+ (Fe 2+ ). The compound name is iron(ii) sulfate or ferrous sulfate Use the name of the compound to determine the formulas for each ion. Then you can write the formula for the compound by balancing the total charge. (a) From the name cobalt(ii), we know that cobalt has a charge of 2+ (Co 2+ ). The formula for chloride ion is Cl. The compound formula is CoCl 2. (b) From the name manganese(ii) we know that manganese has a charge of 2+ (Mn 2+ ). The formula for nitrate ion is NO 3. The compound formula is Mn(NO 3 ) 2. (c) From the name chromium(iii) we know that chromium has a charge of 3+ (Cr 3+ ). The formula for oxide ion is O 2. If the chemical formula is not immediately apparent based on the charges (as in this case), it is often useful to calculate the least common multiple. In this case the least common multiple is 6 (i.e. 3 2 = 6). It takes 2 Cr 2+ to achieve a +6 charge and 3 O 2 to achieve a 6 charge. The compound formula is Cr 2 O 3. (d) From the name copper(ii) we know that copper has a charge of 2+ (Cu 2+ ). The formula for phosphate ion is PO 4 3. If the chemical formula is not immediately apparent based on the charges (as in this case), it is often useful to calculate the least common multiple. In this case the least common multiple is 6 (i.e. 2 3 = 6). It takes 3 Cu 2+ to achieve a +6 charge and 2 PO 4 3 to achieve a 6 charge. The compound formula is Cu 3 (PO 4 ) Use the name of the compound to determine the formulas for each ion. Then you can write the formula for the compound by balancing the total charge. (a) From the name copper(ii), we know that copper has a charge of 2+ (Cu 2+ ). The formula for bromide ion is Br. The compound formula is CuBr 2. (b) From the name iron(iii) we know that iron has a charge of 3+ (Fe 3+ ). The formula for nitrate ion is NO 3. The compound formula is Fe(NO 3 ) 3. (c) From the name chromium(vi) we know that chromium has a charge of 6+ (Cr 6+ ). The formula for oxide ion is O 2. It takes 3 oxide ions to provide a charge of 6. The compound formula is CrO 3. (d) From the name copper(ii) we know that copper has a charge of 2+ (Cu 2+ ). The formula for chlorate ion is ClO 3. The compound formula is Cu(ClO 3 ) Table 3.7 lists the common names for the metal ions. Since nitrate ion has a charge of 1, we determine that the charge of the iron ions in Fe(NO 3 ) 2 and Fe(NO 3 ) 3 are 2+ and 3+, respectively. The Fe 2+ ion is called ferrous ion and the Fe 3+ ion is called ferric ion. The common names for these compounds are ferrous nitrate and ferric nitrate Table 3.7 lists the common names for the metal ions. Since sulfate ion has a charge of 2, we determine that the charge of the copper ions in Cu 2 SO 4 and CuSO 4 are 1+ and 2+, respectively. Cu + ion is called cuprous ion and Cu 2+ ion is called cupric ion. The common names for these compounds are cuprous sulfate and cupric sulfate To write the formulas for the compounds, the ions are combined so that the overall charge is zero. The easiest way to name the compounds in the chart is to first determine the name of each ion. The names of the cations and anions have been listed along with their formulas. The charges must be included in the names of compounds containing iron, nickel, and chromium because their charges cannot be determined by their position on the periodic table. The compound names are derived by combining the cation and anion names. Ca 2+ calcium CaCl 2 calcium chloride Fe 2+ iron(ii) FeCl 2 iron(ii) chloride K + Potassium KCl potassium chloride Mn 2+ manganese(ii) MnCl 2 manganese(ii) chloride Al 3+ aluminum AlCl 3 aluminum chloride + NH 4 ammonium NH 4 Cl ammonium chloride Cl chloride 3-8

9 O 2 oxide CaO calcium oxide FeO iron(ii) oxide K 2 O potassium oxide MnO manganese(ii) oxide Al 2 O 3 aluminum oxide (NH 4 ) 2 O ammonium oxide NO 3 nitrate Ca(NO 3 ) 2 calcium nitrate Fe(NO 3 ) 2 iron(ii) nitrate KNO 3 potassium nitrate Mn(NO 3 ) 2 manganese(ii) nitrate Al(NO 3 ) 3 aluminum nitrate NH 4 NO 3 ammonium nitrate SO 3 2 sulfite CaSO 3 calcium sulfite FeSO 3 iron(ii) sulfite K 2 SO 3 potassium sulfite MnSO 3 manganese(ii) sulfite Al 2 (SO 3 ) 3 aluminum sulfite (NH 4 ) 2 SO 3 ammonium sulfite OH hydroxide Ca(OH) 2 calcium hydroxide Fe(OH) 2 iron(ii) hydroxide KOH potassium hydroxide Mn(OH) 2 manganese(ii) hydroxide Al(OH) 3 aluminum hydroxide NH 4 OH ammonium hydroxide ClO 3 chlorate Ca(ClO 3 ) 2 calcium chlorate Fe(ClO 3 ) 2 iron(ii) chlorate KClO 3 potassium chlorate Mn(ClO 3 ) 2 manganese(ii) chlorate Al(ClO 3 ) 3 aluminum chlorate NH 4 ClO 3 ammonium chlorate 3.54 To write the formulas for the compounds, the ions are combined so that the overall charge is zero. The easiest way to name the compounds in the chart is to first determine the name of each ion. The names of the cations and anions have been listed along with their formulas. The charges must be included in the names of compounds containing iron, nickel, and chromium because their charges cannot be determined by their position on the periodic table. The compound names are derived by combining the cation and anion names. Ba 2+ Fe 3+ Na + Ni 2+ Cr 3+ Ag + Br bromide S 2 sulfide barium BaBr 2 barium bromide BaS barium sulfide iron(iii) FeBr 3 iron(iii) bromide Fe 2 S 3 iron(iii) sulfide sodium NaBr sodium bromide Na 2 S sodium sulfide nickel(ii) NiBr 2 nickel(ii) bromide NiS nickel(ii) sulfide chromium(iii) CrBr 3 chromium(iii) bromide Cr 2 S 3 chromium(iii) sulfide silver AgBr silver bromide Ag 2 S silver sulfide NO 2 nitrite Ba(NO 2 ) 2 barium nitrite Fe(NO 2 ) 3 iron(iii) nitrite NaNO 2 sodium nitrite Ni(NO 2 ) 2 nickel(ii) nitrite Cr(NO 2 ) 3 chromium(iii) nitrite AgNO 2 silver nitrite SO 4 2 sulfate BaSO 4 barium sulfate Fe 2 (SO 4 ) 3 iron(iii) sulfate Na 2 SO 4 sodium sulfate NiSO 4 nickel(ii) sulfate Cr 2 (SO 4 ) 3 chromium(iii) sulfate Ag 2 SO 4 silver sulfate HCO 3 bicarbonate Ba(HCO 3 ) 2 barium bicarbonate Fe(HCO 3 ) 3 iron(iii) bicarbonate NaHCO 3 sodium bicarbonate Ni(HCO 3 ) 2 nickel(ii) bicarbonate Cr(HCO 3 ) 3 chromium(iii) bicarbonate AgHCO 3 silver bicarbonate ClO 4 perchlorate Ba(ClO 4 ) 2 barium perchlorate Fe(ClO 4 ) 3 iron(iii) perchlorate NaClO 4 sodium perchlorate Ni(ClO 4 ) 2 nickel(ii) perchlorate Cr(ClO 4 ) 3 chromium(iii) perchlorate AgClO 4 silver perchlorate 3-9

10 3.55 The formulas for the ions have been listed along with their names. To write the formulas for the compounds, the ions are combined so that the overall charge is zero. potassium K + iron(iii) Fe 3+ strontium Sr 2+ aluminum Al 3+ cobalt(ii) Co 2+ lead(iv) Pb 4+ iodide I KI FeI 3 SrI 2 AlI 3 CoI 2 PbI 4 oxide O 2 K 2 O Fe 2 O 3 SrO Al 2 O 3 CoO PbO 2 sulfate SO 4 2 K 2 SO 4 Fe 2 (SO 4 ) 3 SrSO 4 Al 2 (SO 4 ) 3 CoSO 4 Pb(SO 4 ) 2 nitrite NO 2 KNO 2 Fe(NO 2 ) 3 Sr(NO 2 ) 2 Al(NO 2 ) 3 Co(NO 2 ) 2 Pb(NO 2 ) 4 acetate CH 3 CO 2 KCH 3 CO 2 Fe(CH 3 CO 2 ) 3 Sr(CH 3 CO 2 ) 2 Al(CH 3 CO 2 ) 3 Co(CH 3 CO 2 ) 2 Pb(CH 3 CO 2 ) 4 hypochlorite ClO KClO Fe(ClO) 3 Sr(ClO) 2 Al(ClO) 3 Co(ClO) 2 Pb(ClO) The formulas for the ions have been listed along with their names. To write the formulas for the compounds, the ions are combined so that the overall charge is zero. sodium Na + chromium (II) Cr 2+ calcium Ca 2+ ammonium NH 4 + iron (III) Fe 3+ lead(ii) Pb 2+ chloride Cl NaCl CrCl 2 CaCl 2 NH 4 Cl FeCl 3 PbCl 2 sulfide S 2 Na 2 S CrS CaS (NH 4 ) 2 S Fe 2 S 3 PbS nitrate NO 3 NaNO 3 Cr(NO 3 ) 2 Ca(NO 3 ) 2 NH 4 NO 3 Fe(NO 3 ) 3 Pb(NO 3 ) 2 sulfite NO 2 NaNO 2 Cr(NO 2 ) 2 Ca(NO 2 ) 2 NH 4 NO 2 Fe(NO 2 ) 3 Pb(NO 2 ) 2 hydroxide OH NaOH Cr(OH) 2 Ca(OH) 2 NH 4 OH Fe(OH) 3 Pb(OH) 2 chlorate ClO 3 NaClO 3 Cr(ClO 3 ) 2 Ca(ClO 3 ) 2 NH 4 ClO 3 Fe(ClO 3 ) 3 Pb(ClO 3 )

11 3.57 The formulas for silver and chloride ions are Ag + and Cl. The chemical formula for silver chloride is AgCl The formulas for zinc and chloride ions are Zn 2+ and Cl. Two chloride ions are needed to balance the charge on the zinc ion. The chemical formula for zinc chloride is ZnCl A molecular formula represents the exact numbers of each atom in the molecule. By counting the atoms in each molecule you can arrive at the following formulas: NF 3, P 4 O 10, C 2 H 4 Cl A molecular formula represents the exact numbers of each atom in the molecule. By counting the atoms in each molecule you can arrive at the following formulas: PCl 3, SCl 6, C 3 H 6 F To name molecular compounds, use the prefixes listed in Table 3.9 to indicate the number of each atom in the compound. A prefix is not needed if there is only one atom of the first element. The last element in the name of a diatomic molecular compound always ends in ide. For example, CO is named carbon monoxide (not monocarbon monoxide). (a) phosphorus pentafluoride; (b) phosphorus trifluoride; (c) carbon monoxide; (d) sulfur dioxide 3.62 To name molecular compounds, use the prefixes listed in Table 3.9 to indicate the number of each atom in the compound. The last element in the name of a diatomic molecular compound always ends in ide. A prefix is not needed if there is only one atom of the first element. For example, CO is named carbon monoxide (not monocarbon monoxide). (a) sulfur trioxide; (b) dinitrogen tetroxide; (c) nitrogen dioxide; (d) carbon disulfide 3.63 The prefixes used in naming molecular compounds are listed in Table 3.9. If a prefix is not present, then only one of those atoms is present in the formula. (a) SF 4 ; (b) C 3 O 2 ; (c) ClO 2 ; (d) SO The prefixes used in naming molecular compounds are listed in Table 3.9. If a prefix is not present, then only one of those atoms is present in the formula. (a) CS 2 (b) N 2 O 5 ; (c) BN; (d) IF The central image (B) represents phosphoric acid, H 3 PO 4, with four oxygen atoms attached to one phosphorus atom and hydrogen atoms attached to three of the four oxygen atoms The chemical formula for phosphorous acid is H 3 PO 3. The bottom figure (C) represents phosphorous acid with three oxygen atoms attached to the phosphorus and three hydrogen atoms Acids are derived from the stem of the anion name. The following chart is useful in naming the acids: suffix new prefix new suffix -ide hydro- -ic acid -ite -ate -ous acid -ic acid (a) HF(aq) The anion is fluoride. Since the new suffix is ic, the acid name is hydrofluoric acid. (b) HNO 3 (aq) The anion is nitrate. Since the new suffix is ic, the acid name is nitric acid. (c) H 3 PO 3 (aq) The anion is phosphite. Acids containing phosphorus (and sulfur) are tricky to name. In naming this acid, the stem becomes phosphor. Since the new suffix is -ous, the acid name is phosphorous acid. 3-11

12 3.68 Acids are derived from the stem of the anion name. The following chart is useful in naming the acids: suffix new prefix new suffix -ide hydro- -ic acid -ite -ate -ous acid -ic acid (a) (b) (c) HI(aq) The anion is iodide. Since the suffix is ic, the acid name is be hydroiodic acid. HNO 2 (aq) The anion is nitrite. Since the suffix is -ous, the acid name is nitrous acid. H 3 PO 4 (aq) The anion is phosphate. Acids containing phosphorus (and sulfur) are tricky to name. In naming this acid, the stem becomes phosphor. Since the new suffix is ate, the acid name is phosphoric acid To write the formula for an acid from its name, first determine the formula for the anion. One hydrogen is added to the formula for each negative charge on the anion to balance the charge. An (aq) is added to state that the substance is an acid when dissolved in water. (a) hydrofluoric acid The prefix hydro- with the suffix ic mean that this is a binary acid (composed of only hydrogen and one other element). In this case the anion is fluoride (F ). Since hydrogen forms a 1+ ion and fluoride is a 1 ion, the acid formula is HF(aq). (b) sulfurous acid The ous suffix means that the anion is sulfite (SO 3 2 ). Since hydrogen forms a 1+ ion, two hydrogens are needed to balance the charge. The formula for the acid is H 2 SO 3 (aq). (c) perchloric acid The ic suffix means that the anion is perchlorate (ClO 4 ). Since hydrogen forms a 1+ ion, one hydrogen is needed to balance the charge. The formula for the acid is HClO 4 (aq) To write the formula for an acid from its name, first determine the formula for the anion. One hydrogen is added to the formula for each negative charge on the anion to balance the charge. An (aq) is added to state that the substance is an acid when dissolved in water. (a) hydroiodic acid The prefix hydro- with the suffix ic mean that this is a binary acid (composed of only hydrogen and one other element). In this case the anion is iodide (I ). Since hydrogen forms a 1+ ion and fluoride is a 1 ion, the acid formula is HI(aq). (b) sulfuric acid The ic suffix means that the anion is sulfate (SO 4 2 ). Since hydrogen forms a 1+ ion, two hydrogens are needed to balance the charge. The acid formula is H 2 SO 4 (aq). (c) hypochlorous acid The ous suffix means that the anion is hypochlorite (HClO ). Since hydrogen forms a 1+ ion, one hydrogen is needed to balance the charge. The acid formula is HClO(aq) The formula for nitric acid is HNO 3 (aq). When HNO 3 is dissolved in water, the molecules ionize to form hydrogen ions and nitrate ions (H + and NO 3 ) The formula for hydrobromic acid is HBr. When HBr is dissolved in water, the molecules ionize to form hydrogen ions and bromide ions (H + and Br ) Many substances form crystalline solids, but only two types of substances are electrolytes: acids and ionic compounds (which include bases). Of these two types only ionic compounds form crystalline solids. Only KI, Mg(NO 3 ) 2, and NH 4 NO 3 can be described by these properties. All ionic solids are also brittle because of the strong attraction of the opposite charges in the crystal structure Molecular compounds, with the exception of acids and bases, are non-electrolytes. Only CH 3 OH, H 2 O, and NO 3 are molecular compounds These compounds contain a metal (Zn or Ti) and a nonometal (O). They are ionic compounds. To arrive at the correct formula, make sure the positive and negative charges balance. Since titanium has a 4+ charge 3-12

13 and oxide is 2, the formula is TiO 2. The charge of zinc is always 2+. The correct formula for zinc oxide is ZnO because the charges are balanced Ionic compounds contain either a metal cation or ammonium ion. Ammonium hydroxide is an ionic compound. Since ammonium has a charge of 1+ and hydroxide has a charge of 1 the formula is NH 4 OH Compounds containing only nonmetals are generally molecular (except ammonium compounds). Carbon dioxide and dinitrogen monoxide do not contain metals or ammonium ion, so they are classified as molecular compounds. Formulas for molecular compounds are derived from the prefix (Table 3.9). Absence of a prefix implies only one atom of an element in the formula. Carbon dioxide is CO 2 and dinitrogen monoxide is N 2 O The formulas for sulfur dioxide and nitrogen dioxide are derived from the prefixes (Table 3.9). Absence of a prefix implies only one atom of an element in the formula. Sulfur dioxide and nitrogen dioxide are SO 2 and NO 2, respectively. Recall that acids ending in ous were formed from ions ending in -ite. Sulfurous acid is formed from sulfite, SO 3 2. The acid formula uses as many hydrogen ions, H +, as necessary to balance the charge. The formula for sulfurous acid is H 2 SO 3 (note the number of hydrogens always equals the charge on the anion). Nitrous acid is formed from nitrite, NO 2. The formula for nitrous acid is HNO First classify each compound as either ionic or molecular. Both K 2 S and Na 2 SO 4 are ionic because of the presence of the metal ion. Since potassium and sodium have only one possible charge (1+) we do not specify the charge of the ion in the name. The names of the anions are written without modification so K 2 S and Na 2 SO 4 are named potassium sulfide and sodium sulfate, respectively. SO 2 is a molecular compound and is named using prefixes to indicate the number of each element in the formula. Mono is not used with the first element so the name of SO 2 is sulfur dioxide First classify each compound as either ionic or molecular. Both Na 3 N and KNO 3 are ionic because of the presence of the metal ion. Since sodium and potassium have only one possible charge (1+) we do not specify the charge of the ion in the name. The names of the anions are written without modification so Na 3 N and KNO 3 are named sodium nitride and potassium nitrate, respectively. NO 2 is a molecular compound and is named using prefixes to indicate the number of each element in the formula. Mono is not used with the first element so the name of NO 2 is nitrogen dioxide The first step in naming a compound or substance is to identify whether it is ionic or molecular. Once that is determined, the rules for each type of substance can be applied. (a) molecular, nitrogen trioxide; (b) ion, nitrate; (c) ionic, potassium nitrate; (d) ionic, sodium nitride; (e) ionic, aluminum chloride; (f) molecular, phosphorous trichloride; (g) ionic, titanium(ii) oxide; (h) ionic, magnesium oxide 3.82 The first step in naming a compound or substance is to identify whether it is ionic or molecular. Once that is determined, the rules for each type of substance can be applied. (a) ion, sulfate; (b) ion, sulfide; (c) molecular, carbon dioxide; (d) ion, carbonate; (e) ionic, calcium carbonate; (f) ionic, iron(iii) sulfide; (g) molecular, carbon disulfide; (h) ionic, sodium sulfide 3.83 Once you have determined that a compound is ionic by the presence of a metal cation or ammonium ion, its formula is derived by balancing the charges of the cation and the anion. The ions can be found in Table 3.4 or Figure Otherwise, the formula for molecular compounds is derived from the prefixes (Table 3.9). Note that acids are all molecular compounds, but the formula is derived from the anion it contains (the ion only forms when the substance ionizes in water). For example hydrofluoric acid contains fluoride. Fluoride has the formula F so the acid is HF (one hydrogen ion, H +, is needed to balance the charge). The formulas of acids are followed by (aq) because they are ionized in water. 3-13

14 (a) Ionic. Sodium has a charge of 1+ and carbonate has a charge of 2. To balance the charge, the formula must be Na 2 CO 3. (b) Ionic. Sodium has a charge of 1+ and bicarbonate has a charge of 1. To balance the charge the formula must be NaHCO 3. (c) Acid. Carbonic acid contains carbonate, CO 3 2. To balance the charge with hydrogen ion, H +, the formula must be H 2 CO 3 (aq). (d) Acid. Hydrofluoric acid contains chloride, F. To balance the charge with hydrogen ion, H +, the formula must be HF(aq). (e) Molecular. The prefixes indicate one sulfur and three oxygens; SO 3. (f) Ionic. The copper ion has a charge of 2+ and sulfate has a charge of 2. To balance the charge the formula must be CuSO 4. (g) Acid. Sulfuric acid contains sulfate, SO 4 2. To balance the charge with hydrogen ion, H +, the formula must be H 2 SO 4 (aq). (h) Acid. Hydrosulfuric acid contains sulfide, S 2. To balance the charge with hydrogen ion, H +, the formula must be H 2 S(aq) Once you have determined that a compound is ionic by the presence of a metal cation or ammonium ion, its formula is derived by balancing the charges of the cation and the anion. The ions can be found in Table 3.4 or Figure Otherwise, the formula for molecular compounds is derived from the prefixes (Table 3.9). Note that acids are all molecular compounds, but the formula is derived from the anion it contains (the ion only forms when the substance ionizes in water). For example hydrofluoric acid is contains fluoride. Fluoride has the formula F so the acid is HF (one hydrogen ion, H +, is needed to balance the charge). The formulas of acids are followed by (aq) because they are ionized in water. (a) Molecular. Ammonia is the common (trivial) name for NH 3. These types of names need to be memorized. (b) Ionic. Ammonium has a charge of 1+ and phosphate has a charge of 3. To balance the charge the formula must be (NH 4 ) 3 PO 4. (c) Acid. Hydrochloric acid contains chloride, Cl. To balance the charge with hydrogen ion, H +, the formula must be HCl(aq). (d) Ionic. The potassium ion has a charge of 1+ and hydroxide has a charge of 1. To balance the charge the formula must be KOH. (e) Ionic. The chromium ion has a charge of 3+ and oxide has a charge of 2. To balance the charge the formula must be Cr 2 O 3. (f) Ionic. The magnesium ion has a charge of 2+ and nitrate has a charge of 1. To balance the charge the formula must be Mg(NO 3 ) 2. (g) Ionic. The manganese ion has a charge of 4+ and oxide has a charge of 2. To balance the charge the formula must be MnO 2. (h) Molecular. The prefixes indicate one nitrogen and two oxygens; NO When HCl(g) is a molecular compound it is named hydrogen chloride. However, when it is dissolved in water to form HCl(aq), it is named as an acid because it ionizes. To name a binary acid we replace the anions suffix, ide, with ic and add the prefix hydro-. So chloride is converted to hydrochloric acid When H 2 S(g) is a molecular compound and is named dihydrogen sulfide. However, when it is dissolved in water to form H 2 S(aq), it is named as an acid because it ionizes. To name a binary acid we replace the anions suffix, ide, with ic and add the prefix hydro-. So sulfide is converted to hydrosulfuric acid. Note that in naming sulfur and phosphorus containing acids, we use the entire name of the element and add the suffix ic (a) Prefixes are not used to name ionic compounds; sodium sulfate. (b) Charges are not specified in the name when the cation has only one charge state; calcium oxide. (c) Copper exists in two charge states; 2+ and 1+. The charge must be specified in the name; copper(ii) oxide. (d) The prefix penta- is missing to indicate the presence of 5 chlorine atoms; phosphorus pentachloride. 3-14

15 3.88 (a) The prefix tri- is missing to indicate the presence of 3 fluorine atoms; nitrogen trifluoride. (b) Nickel exists in several charge states, so the charge must be specified in the name; nickel(ii) sulfide. Also, the anion is sulfide, not sulfate. (c) Charges are not specified in the name when the cation has only one charge state; barium nitrate. (d) H 2 O 2 is generally known by its trivial name hydrogen peroxide. The name, dihydrogen peroxide, is also accepted to distinguish it from oxides (i.e. CO 2 ) (a) Sulfide has the formula, S 2, so two potassium atoms are required to balance the charge; K 2 S. (b) The (II) represents the charge of the nickel ion, not the number of nickel ions in the formula. NiCO 3. (c) Nitride is the monatomic ion N 3 ; Na 3 N. (d) The prefix was applied to the wrong element; NI (a) The parentheses are missing; Ca(OH) 2. (b) The charge of aluminum ion is Al 3+ so three Cl are needed; AlCl 3. (c) The prefixes were applied to the wrong elements; N 2 O 3. (d) Phosphide is the monatomic ion P 3 ; K 3 P Charges on the ions are determined by looking at the positions of the atoms on the periodic table, from memory, or from the chemical formula. (a) one sodium ion, Na +, and one chloride ion, Cl (b) one magnesium ion, Mg 2+, and two chloride ions, Cl (c) two sodium ions, Na +, and one sulfate ion, SO 4 2 (d) one calcium ion, Ca 2+, and two nitrate ions, NO Charges on the ions are determined by looking at the positions of the atoms on the periodic table, from memory, or from the chemical formula. (a) one potassium ion, K +, and one bromide ion, Br (b) one ammonium ion, NH 4 +, and one chloride ion, Cl (c) three potassium ions, K +, and one phosphate ion, PO 4 3 (d) one aluminum ion, Al 3+, and three nitrate ions, NO Molecular compounds that are not acids (those that do not have hydrogen first in their formula) are nonelectrolytes. Acids, bases, and water-soluble ionic compounds all produce ions in solution and are, therefore, electrolytes when dissolved in water. (a) electrolyte (base); (b) electrolyte (acid); (c) electrolyte (ionic); (d) nonelectrolyte 3.94 Molecular compounds that are not acids (those that do not have hydrogen first in their formula) are nonelectrolytes. Acids, bases, and water soluble ionic compounds all produce ions in solution and are, therefore, electrolytes when dissolved in water. (a) nonelectrolyte; (b) electrolyte (acid); (c) electrolyte (ionic); (d) electrolyte (base) 3.95 The ions of silver, zinc, and cadmium can each have only one possible charge (see Figure 3.24). They are assumed to have these charges in the compounds they form Besides HCl, which is an acid, the remaining compounds are ionic. (a) H + (aq) and Cl (aq); (b) Na + (aq) and OH (aq); (c) Ca 2+ (aq) and Cl (aq); (d) K + (aq) and NO 3 (aq); (e) Na + (aq) and PO 4 3 (aq) 3.97 The polyatomic ions are listed in Table 3.4 and Figure (a) NO 3 ; (b) SO 3 2 ; (c) NH 4 + ; (d) CO 3 2 ; (e) SO 4 2 ; (f) NO 2 ; (g) ClO Identify the type of compound and then name the compound according to its classification. (a) KBr(s) This is an ionic compound. Since the charge of the cation is predictable from its position on the periodic table it is not specified in the name. The compound is named potassium bromide. 3-15

16 (b) N 2 O 5 (g) This is a molecular compound. Prefixes are used to designate the numbers of each type of atom in the formulas of molecular compounds. The formula name is dinitrogen pentoxide. (c) HBr(aq) This is named as an acid since it is dissolved in water. The ide suffix of bromide indicates that the acid is named hydrobromic acid. (d) Na 2 SO 4 (s) This is an ionic compound. Since the charge of the cation is predictable from its position on the periodic table it is not specified in the name. The compound is named sodium sulfate. (e) Fe(NO 3 ) 3 (s) This is an ionic compound. The charge of the iron ion must be determined from the chemical formula. Since nitrate ion has a charge of 1, the charge of the iron must be 3+ to balance the charge. The name of the compound is iron(iii) nitrate Identify the type of compound and then name the compound according to its classification. (a) MgBr 2 (s) This is an ionic compound. Since the charge of the cation is predictable from its position on the periodic table it is not specified in the name. The compound is named magnesium bromide. (b) H 2 S(g) This is a molecular compound. It is not named as an acid because it is in the gas state. Prefixes are used to designate the numbers of each type of atom in the formulas of molecular compounds. The formula name is dihydrogen sulfide. (c) H 2 S(aq) This is named as an acid since it is dissolved in water. In addition, the ide suffix of sulfide indicates that the acid is named hydrosulfuric acid. (d) CoCl 3 (s) This is an ionic compound. The charge of the cobalt ion must be determined from the chemical formula. Since chloride ion has a charge of 1, the charge of the cobalt is 3+ to balance the contribution of the three chloride ions. The name of the compound is cobalt(iii) chloride. (e) KOH(aq) This is an ionic compound (bases are ionic compounds). Since the charge of the potassium is predictable from its position on the periodic table it is not specified in the name. The compound is named potassium hydroxide. (f) AgBr(s) This is an ionic compound. Since the charge of the silver ion is predictable from its position on the periodic table it is not specified in the name. The compound is named silver bromide Each of these compounds has a common name that you should know. In addition, each compound has a systematic name. (a) NH 3 ammonia or nitrogen trihydride (b) H 2 O water or dihydrogen monoxide (The mono prefix is used when there are more than one oxide possible, see (c).) (c) H 2 O 2 hydrogen peroxide or dihydrogen peroxide To write chemical formulas for ionic compounds, determine the formula for each ion and combine them so that the positive and negative charges balance. In molecular compounds, the formulas are written from the prefixes in the name. (a) Pb 2+ and Cl, PbCl 2 (b) Mg 2+ and PO 4 3, Mg 3 (PO 4 ) 2 (c) Since a prefix is not used on the nitrogen, there is only one nitrogen in the formula. The prefix trimeans three. The formula is NI 3. (d) Fe 3+ and O 2, Fe 2 O 3 (e) Ca 2+ and N 3, Ca 3 N 2 (f) Ba 2+ and OH, Ba(OH) 2 (g) The prefix di- means two and pent- means five. The formula is Cl 2 O 5. (h) NH 4 + and Cl, NH 4 Cl In iron(iii) chloride, the charge on the iron is 3+. Since the charge on chloride ion is 1, you would be looking for FeCl The formula for sodium ion is Na + and bicarbonate ion s formula is HCO 3. One of each ion is needed to balance the charge, so the formula is NaHCO The charge on tin is 2+ and fluoride ion has a 1 charge. The formula for tin(ii) fluoride is SnF 2. The common name for tin(ii) is stannous ion, so the common name is stannous fluoride. 3-16