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Modern ChemistryModern ChemistryChapter 7Chapter 7

Chemical Formulas and Chemical Formulas and Chemical CompoundsChemical Compounds

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Section 1

Chemical Namesand Formulas

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Molecular compounds – for one molecule

Ionic compounds – for one formula unit; the simplest ratio of cations to anions

Chemical Formula

Eight carbon atoms in the

molecule

Eighteen hydrogen atoms in the molecule

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5 ions – two Al 3+ ions and three (SO4) 2-

ions

Chemical Formula

2 Al atoms

4 O atoms4 SO4 ions

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• 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

Definitions

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• Monatomic ions – ions formed from a single atom

• For negative monatomic ions, -ide is added to the root name

Definitions

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Ionic compounds contain

a metal and a nonmetal or

a polyatomic ion !!!

How can I tell if the compound is ionic or

covalent ????

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Ionic Compounds

Writing Fomulas and Naming

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1+

2+3+ 3-2-1-

Charges on Monatomic Ions

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Ag 1+Zn 2+Cu 1+ or 2+Fe/Cr2+ or 3+Sn 2+ or 4+Pb 2+ or 4+See list.

Charges on Transition Metals

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PbO2 and PbOCharges of Metals

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Polyatomic Ions Page 226

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Formulas1. Write the symbols2. 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.

Ionic Compounds

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Names1. 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!!!!

Ionic Compounds

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(charge x subscript)+(charge x subscript) = 0

Ionic Binary CompoundsAluminum Oxide

3+ 2-

(3+ x ) + (2- x ) = 02 3

Al2O3

FO

RM

ULA

S

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Ionic Binary CompoundsAluminum Oxide

3+ 2-

Al2O3

FO

RM

ULA

S

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Mg3N2

Magnesium

Ionic BinaryCompoundsN

AM

ING

Nitrogen

ide

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Pra

cti

ce P

ag

e 2

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1. Write formulas for the binary ionic compounds formed between the following elements:a. potassium and iodineb. magnesium and chlorine c. sodium and sulfurd. aluminum and sulfure. aluminum and nitrogen

2. Name the binary ionic compounds indicated by the following formulas:a. AgCl e. BaOb. ZnO f. CaCl2c. CaBr2

d. SrF2

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Iron (III) Chloride

3+ 1-

(3+ x ) + (1- x ) = 01 3

FeCl3

Ionic Compounds with Transition MetalsF

OR

MU

LAS

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Tin (II) Oxide

2+ 2-

(2+ x ) + (2- x ) = 01 1

SnO

Ionic Compounds with Transition MetalsF

OR

MU

LAS

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Tin (II) Oxide

2+ 2-

SnO

Ionic Compounds with Transition MetalsF

OR

MU

LAS

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Pra

cti

ce P

ag

e 2

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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. CuO c. SnI4b. CoF3 d. FeS

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PbO

Lead

Ionic Compounds with Transition Metals

NA

MIN

G

OxygenideII

( x 1 ) + ( 2- x 1 ) = 02+

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Ionic Compounds with Polyatomic Ions

Ammonium Sulfate+ 2-

(1+ x ) + (2- x ) = 02 1

(NH4)2SO4Parenthesis are needed if the p. ion has a subscript from the crossed charge – outside

the ( ).

FO

RM

ULA

S

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Ca(NO3)2

Calcium

Ionic Compounds with Polyatomic Ions

NA

MIN

G

Nitrate

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Pra

cti

ce P

ag

e 2

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1. Write formulas for the following ionic compounds:a. sodium iodide e. copper(II) sulfateb. calcium chloride f. sodium carbonatec. potassium sulfide g. calcium nitrited. lithium nitrate h. potassium perchlorate

2. Give the names for the following compounds:a. Ag2O

b. Ca(OH)2

c. KClO3

d.NH4OH

e. Fe2(CrO4)3

f. KClO

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Molecular Compounds

Writing Fomulas and Naming

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Pre

fixes f

or

Covale

nt

p. 228

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Formulas1. Write the symbols.2. Use prefixes for subscripts.3. DON’T reduce.

Molecular Compound

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Names1. 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.

Molecular Compound

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Disulfur difluoride

S2F2

Binary Molecular CompoundsF

OR

MU

LAS

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nitrogen

Binary Molecular CompoundsN

AM

ING

oxygenidedi tetra

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Pra

cti

ce P

ag

e 2

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1. Name the following binary molecular compounds:

a. SO3

b. ICl3c. PBr5

2. Write formulas for the following compounds:

a. carbon tetraiodideb. phosphorus trichloridec. dinitrogen trioxide

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• Acids – Chapter 14• Binary Acids – two elements;

hydrogen and one other element• Oxyacids – contain hydrogen, one

other element and oxygen• Acid – typically thought of as an H

donor; usually referred to as a solution of the compound in water.

Acids and Salts

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• 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: CO3

2- carbonate

HCO3 1- hydrogen

carbonate or bicarbonate

Acids and Salts

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Salt

Defi

nit

ion

An

imati

on

p. 230

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Lis

t of

Acid

s

p. 230

Know these acids:

HF, HCl, H3PO4, HNO3, H2SO4 CH3COOH

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Section 3

Oxidation Numbers

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

+3+1

-2

Rules for Assigning Oxidation Numbers

– Atoms in a pure element have an oxidation number of zero – O2 Ox. # = 0

– Fluorine always has ox. # of -1– Oxygen almost always has ox. # of

-2 except in peroxides such as H2O2

– 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?UF6 : Fluorine is -1 x 6 = -6

Uranium +6 {+6 + (-6)} = 0

H2SO4 : Oxygen is -2 (x 4 = -8)Hydrogen is +1 (x 2 = +2)

soSulfur has to be +6

{ (+6) + (+2) + (-8) }= 0

Oxidation Numbers

• What are the oxidation numbers for the chlorate polyatomic ion?

ClO3- : Oxygen is -2 x 3 = -6

Chlorine must be +5 { (+5) + (-6)} = -1 (the ion’s

charge)

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Section 4

Using Chemical Formulas

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 (H2SO4):

element # of atoms x mass (to 2 decimals)

H 2 1.01 = 2.02 amuS 1 32.01=32.01 amuO 4 16.00=64.00 amu

98.03 amu

Formula Mass

• To find the formula mass of Calcium Nitrate Ca(NO3)2

element # of atoms x mass = Ca 1 40.08 =40.08 amuN 2 14.01 =28.02 amuO 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(NO3)2

element # of atoms x mass = Ca 1 40.08 =40.08 gN 2 14.01 =28.02 gO 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 H2SO498.03 grams

1 mole H2SO4

98.03 gramsor

Problems

• How many moles are there in 25 g of H2SO4?

1 mole H2SO498.03 grams

25 g H2SO4 x = 0.255 mol

Problems

• What is the mass of 4.2 moles of H2SO4?

98.03 g H2SO41 mol H2SO4

4.2 mol H2SO4

x = 411.73 mol

Problems

• How many molecules are in 54 g of H2SO4?

6.02 x 1023 molecules H2SO498.03 g H2SO4

54 g H2SO4 x =

3.32 x 1023 molecules

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Section 4

Determining Chemical Formulas

Chemical Formula from % Comp

• Check periodic table for molar masses of each element

• Find moles of each element present (assume 100g 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/molC = 12.01 g/molO = 16.00 g/mol

Empirical formulas

K 56.6 g K x 1 mol K = 1.45 mol 39.10 g K C 8.7 g C x 1 mol C = 0.724 mol 12.01 g CO 34.7 g O x 1 mol O = 2.17 mol 16.00 g OSmallest value = 0.724 Divide all

answers by this number.

Empirical formulas

K = 1.45 mol = 2.00 0.724 molC = 0.724 mol = 1.00 0.724 molO = 2.17 mol = 3.00 0.724 molTherefore, the empirical formula = K2CO3

Name? Potassium Carbonate

Molecular formulas

• Gives the type and actual number of atoms in the compound

• CH2O – empirical formula for glucose

• C6H12O6 – 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 = XEmpirical molar mass

Molecular formulas

Empirical formula of mercury (I) chloride is HgCl. What is the molecular formula, knowing that molar mass is 472.08 g/mol?

Empirical formula HgClMolar mass of unknown = 472.08

g/mol1 mol Hg = 200.59 g/mol1 mol Cl = 35.45 g/molMolar mass of HgCl = 236.04 g/mol

Molecular formulas

472.08 g/mol = 2.00236.04 g/mol2(HgCl) = Hg2Cl2