Naming Inorganic Compounds Names and Formulas of Acids and molecular compounds

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1 Naming Inorganic Compounds Names and Formulas of Acids and molecular compounds

2 Oxidation states Many reactions involve the transfer of electrons from one species to another. Oxidation states are used to keep track of electron transfers. The systematic naming of compounds also makes use of oxidation states. The formation of rust, Fe2O3, iron(iii) oxide: 4Fe(s) + 3O2(g) 2Fe2O3(s) The oxidation state (or oxidation number), of an element in a simple ionic compound is the number of electrons gained or lost by an atom when it forms the compound. In the case of a single-atom ion, it corresponds to the actual charge on the ion. In molecular compounds.

3 Oxidation states Rules for assigning oxidation states follow. These rules cover most cases. The most electronegative element is assigned a negative oxidation state. 1. The oxidation state of the atoms in any uncombined element is zero. This includes polyatomic elements such as H2, O2, P4, and S8. 2. The oxidation state of an element in a monatomic ion is equal to the charge on the ion. 3. In a polyatomic ion, the sum of the oxidation states of the constituent atoms is equal to the charge on the ion. 4. In a neutral compound the sum of the oxidation states is zero. 5. Fluorine, the most electronegative element, has an oxidation state of -1 in all its compounds. 6. Hydrogen has an oxidation state of +1, unless it is combined with metals, in which case it has an oxidation state of -1 (e.g. NaH and CaH2).

4 Oxidation states Rules for assigning oxidation states follow. These rules cover most cases. 7. Oxygen, the second most electronegative element, usually has an oxidation state of -2 in its compounds. There are just a few exceptions: a.oxygen has an oxidation state of -1 in hydrogen peroxide, H2O2, and in peroxides, which contain the O2 2- ion; examples are CaO2 and Na2O2. b.oxygen has an oxidation state of -½ in superoxides, which contain the O2 - ion; examples are KO2 and RbO2. c.when combined with the more electronegative fluorine in OF2, oxygen has an oxidation state of The position of the element in the periodic table helps to assign its oxidation state: e.group 1A elements usually have oxidation states of +1 in all of their compounds. f.group 2A elements usually have oxidation states of +2 in all of their compounds. g.group 3A elements usually have oxidation states of +3 in all of their compounds. h.group 7A elements usually have oxidation states of 2- in binary compounds with metals, with H, with NH, or with a heavier halogen

5 Oxidation states Rules for assigning oxidation states follow. These rules cover most cases. 8.The position of the element in the periodic table helps to assign its oxidation state: Element(s) Common Oxidation States Examples Other Oxidation States H 11 H 2 O, CH 4, NH 4 Cl 21 in metal hydrides, e.g., NaH, CaH 2 Group 1A 11 KCl, NaH, RbNO 3, K 2 SO 4 None Group 2A 12 CaCl 2, MgH 2, Ba(NO 3 ) 2, SrSO 4 None Group 3A 13 AlCl 3, BF 3, Al(NO 3 ) 3, GaI 3 None in common compounds Group 4A Group 5A 23 in binary compounds with metals 23 in NH 4 1, binary compounds with H CO, PbO, SnCl 2, Pb(NO 3 ) 2 CCl 4, SiO 2, SiO 22 3, SnCl 4 Mg 3 N 2, Na 3 P, Cs 3 As NH 3, PH 3, AsH 3, NH 4 1 Many others are also seen for C and Si 13, e.g., NO 2 2, PCl 3 15, e.g., NO 3 2, PO 4 32, AsF 5, P 4 O 10 O 22 2 H 2 O, P 4 O 10, Fe 2 O 3, CaO, ClO 3 12 in OF 2 21 in peroxides, e.g., H 2 O 2, Na 2 O in superoxides, e.g., KO 2, RbO 2 H 2 S, CaS, Fe 2 S 3, Na 2 Se Group 6A (other than O) Group 7A 22 in binary compounds with metals and H 22 in binary compounds with NH in binary compounds with metals and H 21 in binary compounds with NH 4 1 (NH 4 ) 2 S, (NH 4 ) 2 Se MgF 2, KI, ZnCl 2, FeBr 3 NH 4 Cl, NH 4 Br 14 with O and the more electronegative halogens, e.g., SO 2, SeO 2, Na 2 SO 3, SO 3 22, SF 4 16 with O and the more electronegative halogens, e.g., SO 3, TeO 3, H 2 SO 4, SO 4 22, SF 6 Cl, Br, or I with O or with a more electronegative halogen 11, e.g., BrF, ClO 2, BrO 2 13, e.g., ICl 3, ClO 2 2, BrO , e.g., BrF 5, ClO 3 2, BrO , e.g., IF 7, ClO 4 2, BrO 4 2

6 Oxidation states Practice exercise Determine the oxidation states of nitrogen in the following species: (a) N2O4 (b) NH3 Solution (a) The oxidation state of O is -2. The sum of the oxidation states for all atoms in a neutral compound must be zero: nox/atom: x -2 N2O4 total nox: 2x + 4(-2) = 0 or x = +4 (B) The oxidation state of H is +1: nox/atom: x +1 NH3 total nox: x + 3(+1) = 0 or x = -3

7 Oxidation states Practice exercise Determine the oxidation states of nitrogen in the following species: (a) HNO3, (b) NO3 -, (c) N2 Solution (a)the oxidation state of H is +1 and the oxidation state of O is -2. nox/atom: +1 x -2 HNO3 total nox: 1 + x + 3(-2) = 0 or x = +5 (b) The sum of the oxidation states for all atoms in an ion equals the charge on the ion: x -2 - NO3 nox/atom: total nox: x + 3(-2) = -1 or x = +5 (c) The oxidation state of any free element is zero.

8 Names and Formulas of Acids Acids are hydrogen-containing compounds. An acid is a substance whose molecules, when dissolved in water, yield hydrogen ions (H + ). Because a hydrogen atom consists of a proton and an electron, H + is simply a proton. Thus, acids are often called proton donors. When we encounter the chemical formula of an acid, it will be written with H as the first element, as in HCl and HNO3. An acid is composed of an anion connected to enough H ions to neutralize the anion s charge. Thus, the NO3 - ion requires one H + ions, forming HNO3. Hence, he name of an acid is related to the name of its anion Hydrochloric acid, HCl Nitric acid, HNO 3 H Cl N O C Acetic acid, CH 3 COOH

9 Names and Formulas of Acids a. Acids containing anions ending in -ide are named by changing the -ide ending to -ic, adding the prefix hydro- to this anion name, and then following with the word acid: Cl - (chloride) S 2- (sulfide) HCl (hydrochloric acid) H2S (hydrosulfuric acid) b. Acids containing anions whose names end in -ate or -ite are named by changing -ate to -ic and -ite to -ous and then adding the word acid. Prefixes in the anion name are retained in the name of the acid: ClO4 - perchlorate ion HClO4 (perchloric acid) ClO3 - chlorate ion HClO3 (chloric acid) ClO2 - chlorite ion HClO2 (chlorous acid) ClO - hypochlorite ion HClO (hypochlorous acid)

10 Names and Formulas of Acids Anion Acid ide (chloride, Cl ) add H ions hydro ic acid (hydrochloric acid, HCl) ate (chlorate, ClO 3 ) (perchlorate, ClO 4 ) add H ions ic acid (chloric acid, HClO 3 ) (perchloric acid, HClO 4 ) ite (chlorite, ClO 2 ) (hypochlorite, ClO ) add H ions ous acid (chlorous acid, HClO 2 ) (hypochlorous acid, HClO) Notice that the prefixes per- and hypo- are retained in going from the anion to the acid.

11 Names and Formulas of Acids Practice exercise Name the acids (a) HCN, (b) HNO3, (c) H2SO4, (d) H2SO3. SOLUTION (a) The anion from which this acid is derived is CN -, the cyanide ion. Because this ion has an -ide ending, the acid is given a hydro- prefix and an -ic ending: hydrocyanic acid, extremely toxic. (b) Because NO3 - is the nitrate ion, HNO3 is called nitric acid (the -ate ending of the anion is replaced with an -ic ending in naming the acid, without the prefix -hydro). (c) Because SO4 2- is the sulfate ion, H2SO4 is called sulfuric acid. (d) Because SO3 2- is the sulfite ion, H2SO3 is sulfurous acid (the -ite ending of the anion is replaced with an -ous ending). Give the chemical formulas for (a) hydrobromic acid, (b) carbonic acid.

12 Names and Formulas of Molecular Compounds The procedures used for naming binary (two-element) molecular compounds are similar to those used for naming ionic compounds: a. The rule is to name the less electronegative element first and the more electronegative element second. An exception occurs when the compound contains oxygen and chlorine, bromine, or iodine (any halogen except fluorine), in which case oxygen is written last. b. If both elements are in the same group, the lower one is named first. c. The name of the second element is given an -ide ending. d. Greek prefixes are used to indicate the number of atoms of each element (Mono-, Di-, Tri- ect). Cl2O dichlorine monoxide N2O4 dinitrogen tetroxide NF3 nitrogen trifluoride P4S10 tetraphosphorus decasulfide Prefix Meaning mono- 1 di- 2 tri- 3 tetra- 4 penta- 5 hexa 6 hepta- 7 octa- 8 nona- 9 deca- 10