Chapter 7 Chemical Formulas

Chemical Formulas and Names  Subscripts: Indicate the number of each atom in a formula  Hydrocarbons: molecular compounds composed of only carbon and hydrogen.  Ex. Al 2 (SO 4 ) 3 *subscript 2 refers to 2 Al ions *subscript 4 refers to 4 O atoms in the sulfate ion *subscript 3 refers to everything inside the ( ), giving us 3 sulfate ions, with a total of 3 sulfur atoms and 12 oxygen atoms 7-2

Chemical Formulas and Names  Monatomic Ions: ions formed from a single atom  Monatomic cations (+) are named after the element. Ex. Sodium = sodium  Monatomic anions ( -), the end of the element name is dropped and ide is added. Ex. Chlorine = chloride oxygen = oxide 7-3

Balancing Charges  Binary Compounds: compounds composed of two elements  The total positive and negative charges must be equal  Charges are balanced by having more than one of an ion, which is indicated by a subscript  Ex. Magnesium Bromide = Mg +2 and Br -1 ~ +2 and -1 are not balanced, you need two of the bromines to balance the charge: MgBr 2 7-4

Balancing Charges Ex. What is the formula for aluminum oxide? 1.To write balanced ionic formulas, first write the symbols for the ions side by side, cations first: Al 3+ O Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion: Al 2 3+ O Check the subscripts and simplify if necessary. Final answer = Al 2 O 3 7-5

Practice 1) Write balanced formulas for the following binary ionic compounds: a) Sodium chloride:________________________ b) Zinc Oxide:____________________________ c) Aluminum Bromide:_____________________ a) Barium Phosphide:______________________ 7-6

Practice 1) Write balanced formulas for the following binary ionic compounds: a) Sodium chloride:_____NaCl___________________ b) Zinc Oxide:_________ZnO_______________ c) Aluminum Bromide:______AlBr 3 __________ d) Barium Phosphide:__Ba 3 P 2 ________________ 7-7

Naming Binary Compounds  Nomenclature: naming system for chemicals  For binary ionic compounds, name the cation first, then the anion.  Ex. CaCl 2 is calcium chloride. 7-8

Practice 2) What are the names of the following binary ionic compounds? a) Sr 3 N 2 :___________________ b) KI:______________________ c) Li 2 S:____________________ 7-9

Practice 2) What are the names of the following binary ionic compounds? a) Sr 3 N 2 : Strontium Nitride b) KI: Potassium Iodide c) Li 2 S: Lithium sulfide 7-10

Naming Binary Compounds  Some metals form cations with different charges, a roman numeral is used in the name to indicate the charge of the ion. ex. Iron II = Fe +2 Iron III = Fe +3 ex. What is the formula for copper II oxide? Cu +2 O -2 = Cu 2 O 2 = CuO 7-11

Practice 3) What are the formulas for the following binary ionic compounds? a) Iron III sulfide:____________ b) Copper I oxide:____________ 4) What are the names of the following binary ionic compounds? a) CrF 2 :_____________________ b) Pb 3 N 4 :____________________ 7-12

Practice 3) What are the formulas for the following binary ionic compounds? a) Iron III sulfide:__Fe 2 S 3 ______ b) Copper I oxide:___Cu 2 O______ 4) What are the names of the following binary ionic compounds? a) CrF 2 :_____Chromium II Fluoride__ b) Pb 3 N 4 :_____Lead IV Nitride____ 7-13

Polyatomic Ions  Polyatomic Ions: are made up of more than one atom.  Oxyanions: polyatomic ions that contain oxygen. (the name of the ion with the greater number of O atoms ends in ate, with lesser O atoms is ite) ex. NO 2 - = nitrite NO 3 - = nitrate 7-14

Writing Polyatomic Formulas  Charges are balanced just like in binary compounds, but if you need more than one of a polyatomic ion, you must put it in parenthesis with your subscript on the outside. ex. What is the formula for tin IV sulfate? Sn 4+ SO 4 2- = Sn(SO 4 )

Practice 5) Write the formulas for the following ionic compounds: a) Sodium iodide:_____________ b) Lithium nitrate:_____________ c) Copper II sulfate:___________ d) Sodium Carbonate:__________ e) Potassium perchlorate:_______ 7-16

Practice 5) Write the formulas for the following ionic compounds: a) Sodium iodide:____NaI_____ b) Lithium nitrate:____LiNO 3 _____ c) Copper II sulfate:__CuSO 4 _____ d) Sodium Carbonate:____Na 2 CO 3 ___ e) Potassium perchlorate:__KClO 4 __ 7-17

Practice 6)Write the names for the following ionic compounds: a) Ca(OH) 2 ____________________ b) KClO 3 :______________________ c) NH 4 OH:_____________________ d) Fe 2 (CrO 4 ) 3 :___________________ e) KClO:_______________________ 7-18

Practice 6)Write the names for the following ionic compounds: a) Ca(OH) 2 :__calcium hydroxide____ b) KClO 3 :___potassium chlorate_____ c) NH 4 OH:___ammonium hydroxide_ d) Fe 2 (CrO 4 ) 3 :__iron III chromate__ e) KClO:____potassium hypochlorite_ 7-19

Naming Binary Molecular Compounds  Naming Based on Prefixes:  Covalently bonded binary molecules are named using prefixes to designate the number of atoms in the molecule. The only exception is that if the first atom in the molecule has only one atom, the mono prefix is dropped (understood)  ex. CO is carbon monoxide CO 2 is carbon dioxide 7-20

Practice 7) Name to following binary molecular compounds using the prefix system: a) H 2 0:_____________________________ b) N 2 O 3 :____________________________ c) P 4 O 10 :___________________________ 8) Write the formula for the following binary molecular compounds: a) Sulfur dioxide:__________________________ b) Phosphorous pentabromide:________________ c) Carbon tetrachloride:_____________________ 7-21

Practice 7) Name to following binary molecular compounds using the prefix system: a) H 2 O:_____dihydrogen monoxide______ b) N 2 O 3 :_____dinitrogen trioxide_______ c) P 4 O 10 :_tetraphosphorous decaoxide___ 8) Write the formula for the following binary molecular compounds: a) Sulfur dioxide:_______SO 2 ______________ b) Phosphorous pentabromide:____PBr 5 _______ c) Carbon tetrachloride:_____CCl 4 __________ 7-22

Acids  Binary Acid: consists of two elements, usually hydrogen and one of the halogens.  Oxyacid: contain hydrogen, oxygen and a third element.  Salt: an ionic compound composed of a cation and the anion from an acid. 7-23

Oxidation Numbers  Oxidation Numbers: a.k.a. oxidation states, indicates the general distribution of electrons among the bonded atoms in a molecular compound or a polyatomic ion. 7-24

Oxidation Numbers ~ Rules 1) Atoms of a pure element have an ox. # of zero 2) More electroneg. elements in binary molecular compounds have an ox. # equal to their charge as an anion, the less electroneg. elements have an ox. # equal to the cation. 3) Fluorine has an ox. # of -1. 4) Oxygen has an ox. # of -2 (exceptions are peroxides, -1, or when bonded Fluorine, +2) 5) Hydrogen has an ox. # of +1 when bonded with more electronegative elements, -1 when bonded with metals. 6) The algebraic sum of the ox. # in a neutral compound is zero. 7) The algebraic sum of the ox. # in a polyatomic ion is equal to the charge of the ion. 8) Ox. # can be assigned to atoms in ionic compounds. 9) A monatomic ion has an ox. # equal to the charge of the ion. 7-25

Oxidation Numbers ~ Examples  What are the oxidation numbers for the atoms in the following compounds:  H 2 O: O is -2, H is +1  HNO 3 : H is +1, O is -2 (x3 = -6), N must be +5  P 4 O 10 : O is -2 (x10 = -20), P must be +5 (x 4 = +20)  ClO 3 - : O is -2(x3 = -6), Cl must be

Practice 9) What are the oxidation numbers for the atoms in the following compounds? a) PCl 3 :___________________________ b) CF 4 :_____________________________ c) PbO 2 :____________________________ _ 7-27

Practice 9) What are the oxidation numbers for the atoms in the following compounds? a) PCl 3 :__ P +3, Cl -1_________ b) CF 4 :____F -1, C +4___________ c) PbO 2 :__Pb +4, O -2__________ 7-28

Using Chemical Formulas  Formula Mass: the sum of the atomic mass of all the atoms represented in the formula. (this is calculated just like molar mass, but the units are amu instead of g/mol) Ex. What is the formula mass of water? H 2 O: H = 1.01 amu x 2 = 2.02 amu O = amu x 1 = amu Formula Mass of H 2 O = amu 7-29

Practice 11) What is the formula mass of ammonia? NH 3 : N = amu x 1 = amu H = 1.01 amu x 3 = 3.03 amu Formula Mass of NH 3 = amu 7-30

Conversions Mass/Particles using molar mass: How many formula units are in 29.36g of NaCl? 29.36g x 6.02 x units 58.44g NaCl = x units 7-31

Conversions Mass/Particles using molar mass: What is the mass of 5.39 x molecules of H 2 O? 5.39 x x g molecules 6.02 x molecules = 16.1 g water 7-32

Practice 12) How many atoms of hydrogen are in g of H 2 O? 13) What is the mass of 7.89 x formula units of BaCl 2 ? 7-33

Practice 12) How many atoms of hydrogen are in g of H 2 O? 35.67g x 6.02 x molecules x 2 atoms H = x gmolecule atoms 12) What is the mass of 7.89 x formula units of BaCl 2 ? 13) 7.89 x units x____ g = 2730 g 6.02 x units 7-34

Percent Composition  Percent Composition: the percentage by mass of each element in a compound. % Comp. = total mass of element x 100 total mass of compound Ex. What is the % of H and O in one mole of H 2 O? % H = 2 x 1.01 g H x 100 = 11.2% g H 2 O % O = 1 x g O x 100 = 88.8% g H 2 O 7-35

Practice 14) What is the percent comp. of HClO 3 ? Molar Mass = g/mol %H = 1.01 x 100 = 1.20% H %Cl = x 100 = 42.0% Cl %O = x 100 = 56.8% O

Empirical Formulas  Empirical Formula: consists of the symbols for the elements combined in a compound, with subscripts showing the smallest whole number ratio of the different atoms in the compound. Ex. Empirical formula = H 2 O Molecular formula = H 4 O 2 = H 6 O

Empirical Formulas An unknown compound was found to be 75% C and 25% H. What is the empirical formula? A 100.0g sample would have 75.0g C and 25.0g H: 75.0 g C x 1.0 mol C = 6.25 mol C atoms g C 25.0 g H x 1.0 mol H = 25.0 mol H atoms 1.01 g H Make a ratio of Moles of each element divided by the smallest number of moles. C: 6.25 = 1 H = 25.0 = 4 C:H is 1: the compound is CH

Empirical Formulas 15) Now you try one: determine the empirical formula for a compound containing 7.30 g Na, 5.08 g S and 7.62 g O g Na x 1.0 mol Na = mol Na atoms g Na 5.08 g S x 1.0 mol S = mol S atoms g S 7.62 g O x 1.0 mol O = mol O g O Na: = 2.01 S = = 1 O = = The compound is Na 2 SO

Molecular Formulas Molecular Formulas give the actual number of atoms of each element in a molecular compound. This is always a whole number multiple of the empirical formula. By dividing the molar mass by the empirical formula mass, you get the molecular formula. 7-41

Practice 16) Find the molecular formula for a compound that contains 4.90 g N and 11.2 g O with a molar mass of 92.0 g/mol g N x 1.0 mol N = mol N g N 11.2 g O x 1.0 mol O = mol O g O N: = 1.00 mol N O = = 2.00 mol O NO 2 is the empirical formula. Molar mass = 92.0g/mol = 2 Empirical formula mass 46.01g/mol Molecular formula = 2 X empirical formula = N 2 O

Ch. 7 The End!