1 Chemical Formulas Chapter 7
2 I. Reviewing Ions 1. Ion = atom or a group of bonded atoms with a positive or negative charge.
3 I. Reviewing Ions 2. Cation = ion with a POSITIVE (+) charge. a) Forms when an atom LOSES one or more valence electrons. b) Ex: Be +2 forms because beryllium Loses 2 valence electrons.
4 I. Reviewing Ions * Be has the following electron configuration: 1s 2 2s 2 * How many VALENCE electrons does Be have? * 2 valence electrons
5 I. Reviewing Ions * How many protons and electrons does a Be atom have? * 4 protons and 4 electrons * How many protons and electrons does Be +2 have? * 4 protons and 2 electrons * Creating a +2 ion.
6 I. Reviewing Ions 3. Anion = ion with a NEGATIVE (- ) charge. a) Forms when an atom GAINS one or more valence electrons. b) Ex: F - 1 forms because fluorine Gains 1 valence electron.
7 I. Reviewing Ions * F has the following electron configuration: 1s 2 2s 2 2p 5 * How many VALENCE electrons does F have? 7 * valence electrons.
8 I. Reviewing Ions * How many protons and electrons does the F atom have? * 9 protons and 9 electrons * How many protons and electrons does F - 1 have? * 9 protons and 10 electrons * Creating a - 1 ion
9 I. Reviewing Ions 4. Monatomic Ion = ion formed from only ONE atom. a) Ex: Na +1, Ca +2, N - 3, F - 1 b) Note: all monatomic anions end in ide * Ex: atom = oxygen; ion = oxide * Ex: atom = chlorine; ion = chloride * Ex: atom = sulfur; ion = sulfide
10 I. Reviewing Ions 5. Polyatomic ion = ion formed from two or more atoms bonded together with a charge. a) Ex: SO 4-2, Hg 2 +2, OH - 1, CN - 1
11 I. Reviewing Ions 6. Classify the following as monatomic anion, monatomic cation, polyatomic anion, or polyatomic cation. a) Li +1 = Monatomic cation b) O = Polyatomic anion c) NH +1 4 = Polyatomic cation d) S - 2 = Monatomic anion
12 I. Reviewing Ions I. REVIEWING IONS 7. REMEMBER- Rules For Assigning Ion Charges: 7. REMEMBER Rules for assigning Ion charges:
13 I. Reviewing Ions 8. Roman Numerals * Sometimes an atom is able to give away a various number of electrons and be stable. * The Roman numerals tell how many electrons have been given away and that will be the POSITIVE charge. * Ex: iron (II) and iron (III) * Fe +2 and Fe +3
14 II. Writing Ionic Formulas 1. Ionic compounds are formed by two ions of opposite charge (cations are + and anions are - ) and that they are held together by a relatively weak attraction between the ions.
15 II. Writing Ionic Formulas 2. KEY IDEA Ionic Compounds: * Usually metal and nonmetal elements combine. * Are NEUTRAL compounds
16 II. Writing Ionic Formulas * The simplest whole number ratio between the cation & anion creates the ionic formula. * The next charge is zero, forming a neutral ionic compound * Ex: MgCl 2 * 1 magnesium ion : 2 chloride ions * Ex: KBr * 1 potassium ion : 1 bromide ion * Ex: Ca 3 (PO 4 ) 2 * 3 calcium ions : 2 phosphate ions ons
17 II. Writing Ionic Formulas 3. Care must be taken that subscripts are correct. * Ex: NaCl vs. CaCl 2
18 II. Writing Ionic Formulas 4. Why does the chlorine have a subscript of 2 in one chemical formula but not in the other? * Look at the ion charges!
19 Look at the ION charges! * Sodium is Na +1 and chloride is Cl - 1 * A +1 and a - 1 charge form an ionic compound with a zero charge! Ca +2 Cl - 1 * Calcium is and chloride is * NOW 2 chloride ions are needed in order to form a neutral compound
20 II. Writing Ionic Formulas 5. All IONIC compounds are neutral. So the algebraic sum of the charges has to equal zero!
21 II. Writing Ionic Formulas * Ex: Aluminum sulfate has the following chemical formula: Al 2 (SO 4 ) 3 * A chemical formula for this ionic compound shows that 2 Al +3 ions and 3 SO 4-2 ions are needed in order to form a neutral compound.
22 6. Examples of Forming Ionic compounds * Example #1: Write a formula for aluminum chloride. * What are the charges of the ions? Al +3 * and Cl - 1 * What do the charges mean? * Aluminum Loses 3 electrons * Chlorine Gains 1 electron
23 How is aluminum chloride formed? * Use electron- dot formulas to illustrate the formation of ionic bonds involving Al and Cl.
24 How is aluminum chloride formed? * It takes 3 chlorine atoms to gain 3 electrons that one aluminum atom can donate. * When this transfer occurs, 1 aluminum ion will be formed and three chloride ions will be formed. * These particles will all be held together by the opposite electrostatic charges. * The formula is AlCl 3
26 Example #2: Write a formula for sodium sulfide. * What are the charges of the ions? * Na +1 and S - 2 * What is the ratio or combination that these ions must form in order to form a NEUTRAL compound? * 2 sodium ions and 1 sulfide ion * Write the formula for sodium sulfide: Na 2 S
27 Rules for Writing Ionic Formulas
28 7. Rules for writing ionic formulas: 1. The subscript 1 is understood when NO subscript is present and is not written. 2. Use parentheses around polyatomic ions when adding additional subscripts * PROTECT POLYATOMICS WITH PARENTHESES!! (Parentheses)
29 7. Rules for writing ionic formulas: 3. Write the symbol for the positive ion (cation) first, following by the negative ion (anion) 4. Determine the simplest whole number ratio between the cation and anion
30 7. R ules f or W riting I onic F ormulas: 7. Rules For Writing Ionic Formulas: Use the criss-cross method- the NUMBERS of* the positive and negative charges can be Use the criss- cross method- the NUMBERS of the crossed over to give thecan correct subscripts positive and negative charges be crossed over to give the correct subscripts to the opposite ion. to the opposite ion.
31 II. Writing Ionic Formulas * Ex #1: What is the formula of the compound formed by the ions of magnesium and bromine? Ions = Mg +2 and Br - 1 Formula = Mg Br 2
32 II. Writing Ionic Formulas * Ex #2: Aluminum Sulfide (use the criss- cross method) Al +3 S - 2 * Ions = * Formula = Al 2 S 3
33 II. Writing Ionic Formulas * Ex #3: Magnesium oxide * Ions = Mg +2 O - 2 * Formula = Mg 2 O 2 * We must reduce this to the lowest terms! MgO * The final answer is he lowest
34 II. Writing Ionic Formulas * Ex #4: Sodium Peroxide * Polyatomic NO parentheses and NO reduction Na +1 O 2-2 * Ions = * Formula = Na 2 O 2 * NO REDUCTION this is the correct formula for this compound since we cannot reduce a subscript which is already set as a part of the original ion!
35 II. Writing Ionic Formulas * Ex #5: Copper II Sulfate * Polyatomic NO parentheses and reduction Cu +2 SO 4-2 * Ions = * Formula = CuSO 4
36 II. Writing Ionic Formulas * Ex #6: Calcium nitrate * Polyatomic PROTECT with PARENTHESES * You cannot alter the subscripts that come with polyatomic ions, we use parentheses! Ca +2 NO 3-1 * Ions = ntheses Ca(NO 3 ) 2 * Formula =
37 II. Writing Ionic Formulas * Note: NEVER use parentheses around monatomic ions (Na, Li, Fe, Cu, etc). Only polyatomic ions (SO 4, MnO 4, NH 4, PO 3, etc.) will require the use of parentheses..
38 Writing Ionic Formulas Videos * Introduction video: * https://www.youtube.com/watch?v=vscoyh6m46m * Transitional metals * https://www.youtube.com/watch?v=cyfgoowjvgg (stop at 3:24) * https://www.youtube.com/watch?v=5xpdaxnx7je * Polyatomic ions * https://www.youtube.com/watch?v=3k5v3kxxli8
39 II. Naming Ionic Compounds 1. Rules: a) Determine the name of the cation and anion that is present. * Positively charged ion name comes 1 st * Negatively charged ion name comes 2 nd * Ex: AgCl = silver chloride * Ex: Ba 3 (PO 4 ) 2 = barium phosphate
40 II. Naming Ionic Compounds 1. Rules: b) Ions with more than one charge, you have to figure out the charge and use the correct roman numerals! * Always use the anions charge to figure out the correct cation.
41 * Ex: FeO * Determine the charge of the anion (negative ion) * Oxide s charge is * So Fe has the have a +2 charge because FeO is a NEUTRAL compound! * Ions have to be: and * So it is Iron II oxide - 2 Fe +2 O - 2
42 II. Naming Ionic Compounds * Ex: Cr 2 (SO 4 ) 3 * Determine the charge of the anion (negative ion) * Sulfate s charge is and you have 3 ions for a total charge of for the anions * So the 2 Cr ions have to have a total charge of since Cr 2 (SO 4 ) 3 is a NEUTRAL compound.
43 II. Naming Ionic Compounds: * Ex: Cr 2 (SO 4 ) 3 * Ions have to be Cr +3 and SO Chromium III Sulfate * So it is
44 Naming Ionic compounds video * Binary ionic compounds * https://www.youtube.com/watch?v=ww_hvrh0luk * Transition metals * https://www.youtube.com/watch?v=cyfgoowjvgg (start at 6:16)
45 MOLECULAR FORMULAS
46 III. Writing Molecular Formulas 1. Chemical formula for a molecular compound is called a molecular formula. ecular formula
47 III. Writing Molecular Formulas 2. Molecular formula = formula showing the types and numbers of atoms combined in a single molecule of a molecular compound. * Molecular compounds are usually 2 nonmetals
48 III. Writing Molecular Formulas 3. Prefixes tell you what the subscript will be! * Ex: Carbon monoxide à CO * Ex: Carbon dioxide à CO 2 * Ex: Dinitrogen trioxide à N 2 O 3
49 III. Writing Molecular Formulas Prefixes: 1 Mono- 6 Hexa- 2 Di- 7 Hepta- 3 Tri- 8 Octa- 4 Tetra- 9 Non- 5 Penta- 10 Deca-
50 IV. Naming Molecular Compounds 1. Rules for naming molecular compounds: a) A prefix is used with the name of the FIRST element ONLY if there is more than one atom of that element is present. b) The second element is named by combining a prefix and changing the ending to ide
51 IV. Naming Molecular Compounds * Ex: NO is called Nitrogen monoxide * Ex: N 2 O is called Dinitrogen monoxide
52 IV. Naming Molecular Compounds 2. Hints to use when molecular and ionic compounds are on the same worksheet/test: * Determine if the compound is molecular or ionic. * Molecular compounds ONLY contain NONMETALS.
53 IV. Naming Molecular Compounds * Ionic compounds ONLY contain METALS and NONMETALS * Compounds that contain ammonium ion (NH 4+ ) are IONIC compounds. * Remember that there is an ion dichromate. So dichromate would be part of an IONIC compound! would be
54 Molecular formulas video * https://www.youtube.com/watch?v=ztmhbktgi- M