Modern Chemistry Chapter 7 Chemical Formulas and Chemical

Modern Chemistry Chapter 7 Chemical Formulas and Chemical Compounds 1

Section 1 Chemical Names and Formulas 2

Chemical Formula Eight carbon atoms in the molecule Eighteen hydrogen atoms in the molecule Molecular compounds – for one molecule Ionic compounds – for one formula unit; the simplest ratio of cations to anions 3

Chemical Formula 2 Al atoms 4 O atoms 4 SO 4 ions 5 ions – two Al 3+ ions and three (SO 4) 2 - ions 4

Definitions • Binary Compound – compound with only two types of atoms • Nomenclature – a naming system • Salt- an ionic compound composed of a cation and an anion from an acid 5

Definitions • Monatomic ions – ions formed from a single atom • For negative monatomic ions, -ide is added to the root name 6

How can I tell if the compound is ionic or covalent ? ? Ionic compounds contain metal and a nonmetal or a a polyatomic ion !!! 7

Writing Fomulas and Naming Ionic Compounds 8

Charges on Monatomic Ions + 1 2+ + 3 32 1 9

Charges on Transition Metals Ag Zn Cu Fe/Cr Sn Pb See list. 1+ 2+ 2+ 2+ or or 2+ 3+ 4+ 4+ 10

Charges of Metals Pb. O 2 and Pb. O 11

Polyatomic Ions Page 226 12

Ionic Compounds Formulas 1. Write the symbols 2. Determine the charges 1. Monatomic ions from the periodic table 2. Transition metals from a roman numeral 3. Polyatomic ions from sheet. 3. Cross the charges. 4. Reduce to lowest ratio. 13

Ionic Compounds Names 1. Write the cation name. 2. Write the anion name. • Add –ide to the anion if monatomic 3. Add the roman numeral for any transition metal. 4. NO PREFIXES!!!! 14

Ionic Binary Compounds FORMULAS Aluminum Oxide 3+ (3+ x 2 ) + (2 - x 2 - 3 )=0 Al 2 O 3 (charge x subscript)+(charge x subscript) = 0 15

FORMULAS Ionic Binary Compounds Aluminum Oxide 3+ 2 - Al 2 O 3 16

NAMING Ionic Binary. Compounds Mg 3 N 2 ide Magnesium Nitrogen 17

Practice Page 223 1. Write formulas for the binary ionic compounds formed between the following elements: a. potassium and iodine b. magnesium and chlorine c. sodium and sulfur d. aluminum and sulfur e. aluminum and nitrogen 2. Name the binary ionic compounds indicated by the following formulas: a. Ag. Cl e. Ba. O b. Zn. O f. Ca. Cl 2 c. Ca. Br 2 d. Sr. F 2 18

FORMULAS Ionic Compounds with Transition Metals Iron (III) Chloride 3+ (3+ x - x ) + (1 1 1 - 3 )=0 Fe. Cl 3 19

FORMULAS Ionic Compounds with Transition Metals Tin (II) Oxide 2+ (2+ x - x ) + (2 1 2 - 1 )=0 Sn. O 20

FORMULAS Ionic Compounds with Transition Metals Tin (II) Oxide 2+ 2 - Sn. O 21

Practice Page 225 1. Write the formula and give the name for the compounds formed between the following ions: a. Cu 2+ and Br − d. Hg 2+ and S 2− b. Fe 2+ and O 2− e. Sn 2+ and F − c. Pb 2+ and Cl − f. Fe 3+ and O 2− 2. Give the names for the following compounds: a. Cu. O c. Sn. I 4 b. Co. F 3 d. Fe. S 22

NAMING Ionic Compounds with Transition Metals Pb. O ( 2+ x 1 ) + ( 2 - x 1 ) = 0 Lead II Oxygen ide 23

FORMULAS Ionic Compounds with Polyatomic Ions Ammonium Sulfate + (1+ x 2 ) + (2 - x 2 - 1 )=0 (NH 4)2 SO 4 Parenthesis are needed if the p. ion has a subscript from the crossed charge – outside the ( ). 24

NAMING Ionic Compounds with Polyatomic Ions Ca(NO 3)2 Calcium Nitrate 25

Practice Page 227 1. Write formulas for the following ionic compounds: a. sodium iodide e. copper(II) sulfate b. calcium chloride f. sodium carbonate c. potassium sulfide g. calcium nitrite d. lithium nitrate h. potassium perchlorate 2. Give the names for the following compounds: a. Ag 2 O b. Ca(OH)2 c. KCl. O 3 d. NH 4 OH e. Fe 2(Cr. O 4)3 f. KCl. O 26

Writing Fomulas and Naming Molecular Compounds 27

p. 228 28 Prefixes for Covalent

Molecular Compound Formulas 1. Write the symbols. 2. Use prefixes for subscripts. 3. DON’T reduce. 29

Molecular Compound Names 1. Write the name of the elements. – Order: Smaller group number first; – Same group? Greater period number first. 2. Add –ide to the second element. 3. Add prefixes to each element for the number of atoms. 30

FORMULAS Binary Molecular Compounds Disulfur difluoride S 2 F 2 31

NAMING Binary Molecular Compounds di nitrogen tetra oxygen ide 32

Practice Page 229 1. Name the following binary molecular compounds: a. SO 3 b. ICl 3 c. PBr 5 2. Write formulas for the following compounds: a. carbon tetraiodide b. phosphorus trichloride c. dinitrogen trioxide 33

Acids and Salts • Acids – Chapter 14 • Binary Acids – two elements; hydrogen and one other element • Oxyacids – contain hydrogen, one other element and oxygen • Acid – a solution of the compound in water. 34

Acids and Salts • Salt – an ionic compound • Made from – the cation of a base and – the anion of an acid • Some retain an H in the anion – Example: CO 3 2 - carbonate HCO 3 1 - hydrogen carbonate or bicarbonate 35

p. 230 36 Salt Definition Animation

p. 230 37 List of Acids

Section 3 Oxidation Numbers 38

Oxidation Numbers • Oxidation numbers are numbers assigned to the atoms in a molecular compound or ion that indicates the general distribution of electrons among bonded atoms. • Oxidation numbers are not actual charges. • Oxidation numbers can be useful in naming compounds and writing formulas. +2 -1 +1 +3 -2

Rules for Assigning Oxidation Numbers – Atoms in a pure element have an oxidation number of zero – O 2 Ox. # = 0 – Fluorine always has ox. # of -1 – Oxygen almost always has ox. # of -2 except in peroxides such as H 2 O 2 – then it is a -1.

Rules for Assigning Oxidation Numbers • (Rules continued): – Hydrogen’s ox. # is +1 unless it is with metals – then it is -1 – The sum of the ox. # in molecules must be zero, but in polyatomic ions, it is equal to the ions charge.

Oxidation Numbers • What are the oxidation numbers for each atom in these compounds? UF 6 : Fluorine is -1 x 6 = -6 Uranium +6 {+6 + (-6)} = 0 H 2 SO 4 : Oxygen is -2 (x 4 = -8) Hydrogen is +1 (x 2 = +2) so Sulfur has to be +6 { (+6) + (+2) + (-8) }= 0

Oxidation Numbers • What are the oxidation numbers for the chlorate polyatomic ion? Cl. O 3 - : Oxygen is -2 x 3 = -6 Chlorine must be +5 { (+5) + (-6)} = -1 (the ion’s charge)

Section 4 Using Chemical Formulas 44

Formula Mass • With a chemical formula, you can calculate many characteristic values for a compound. • Formula Mass: – Compounds have masses – just like elements.

Formula Mass • Formula Mass: – The formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented in its formula. – To find the mass of a compound simply add the masses of the atoms that make up the compound. Units are amu’s.

Formula Mass • To find the formula mass of sulfuric acid (H 2 SO 4): element # of atoms x mass (to 2 decimals) H 2 1. 01 = 2. 02 amu S 1 32. 01=32. 01 amu O 4 16. 00=64. 00 amu 98. 03 amu

Formula Mass • To find the formula mass of Calcium Nitrate Ca(NO 3)2 element # of atoms x mass = Ca 1 40. 08 =40. 08 amu N 2 14. 01 =28. 02 amu O 6 16. 00= 96. 00 amu 164. 10 amu

Molar Mass • Molar Mass – The mass of a mole of any substance is equal to its formula mass – except instead of amu’s it is in grams. – Formula mass of sulfuric acid = 98. 03 amu – Molar mass of sulfuric acid = 98. 03 grams

Molar Mass • To find the molar mass of Calcium Nitrate Ca(NO 3)2 element # of atoms x mass = Ca 1 40. 08 =40. 08 g N 2 14. 01 =28. 02 g O 6 16. 00= 96. 00 g 164. 10 g

Percentage Composition • It is sometimes useful to know what the percentage of a compound is an element. • What percentage of water is oxygen? H: 1. 01 x 2 = 2. 02 O: 16. 0 x 1 = 16. 0 Molar Mass= 18. 02 g 16. 0 ÷ 18. 02 = 88. 79%

Molar Mass • Molar Mass can be used as a conversion factor. 1 mole H 2 SO 4 or 98. 03 grams 1 mole H 2 SO 4

Problems • How many moles are there in 25 g of H 2 SO 4? 25 g H 2 SO 4 1 mole H 2 SO 4 x 98. 03 grams = 0. 255 mol

Problems • What is the mass of 4. 2 moles of H 2 SO 4? 4. 2 mol H 2 SO 4 x 98. 03 g H 2 SO 4 1 mol H 2 SO 4 = 411. 73 mol

Problems • How many molecules are in 54 g of H 2 SO 4? 54 g H 2 SO 4 x 6. 02 x 1023 molecules H 2 SO 4 98. 03 g H 2 SO 4 3. 32 x 1023 molecules =

Section 4 Determining Chemical Formulas 56

Chemical Formula from % Comp • Determine the chemical formula of a compound from the percent composition data • Check periodic table for molar masses of each element • Find moles of each element present (assume 100 g since we are working with percentages) • To determine the simplest ratio of moles in the compound, select the smallest number of moles calculated and divide the other moles calculated by that number • Write the formula using the smallest whole number ratio of elements

Empirical formulas • Simplest formula • Consists of element symbols and subscripts showing the numbers of each element • Really, subscripts represent the smallest whole number ratios

Empirical formulas What is the empirical formula of a compound containing 56. 6% K, 8. 7% C and 34. 7 % O ? K= 39. 10 g C = 12. 01 g O = 16. 00 g

Empirical formulas K 56. 6 g K x 1 mol K 39. 10 g K C 8. 7 g C x 1 mol C 12. 01 g C O 34. 7 g O x 1 mol O 16. 00 g O Smallest value = 0. 724 by this number. = 1. 45 mol = 0. 724 mol = 2. 17 mol Divide all answers

Empirical formulas K = 1. 45 mol = 2. 00 0. 724 mol C = 0. 724 mol = 1. 00 0. 724 mol O = 2. 17 mol = 3. 00 0. 724 mol Therefore, the empirical formula = K 2 CO 3 Name? Potassium Carbonate

Molecular formulas • Gives the type and actual number of atoms in the compound • CH 2 O – empirical formula for glucose • C 6 H 12 O 6 – molecular formula for glucose • So far, we have been studying ionic compounds, so molecular and empirical formulas were the same • In most compounds, however, not the same

Molecular formulas • Molecular formulas can be determined from empirical formulas X (empirical formula) = molecular formula (X is a whole number) Also true. . . Molecular molar mass = X Empirical molar mass

Molecular formulas Empirical formula of mercury (I) chloride is Hg. Cl. What is the molecular formula, knowing that molar mass is 472. 08 g/mol? Empirical formula Hg. Cl Molar mass of unknown = 472. 08 g/mol 1 mol Hg = 200. 59 g/mol 1 mol Cl = 35. 45 g/mol Molar mass of Hg. Cl = 236. 04 g/mol

Molecular formulas 472. 08 g/mol = 2. 00 236. 04 g/mol 2(Hg. Cl) = Hg 2 Cl 2 Name? dimercury dichloride