Naming Chemical Compounds3221.3.1, 3221.3.2

Objectives

TLW write chemical formulas of ionic and molecular compounds.

TLW name chemical compounds using the correct system.

TLW use polyatomic ions.

Significance of a chemical formula• Recall that a chemical formula indicates the relative

number of atoms of each kind in a chemical formula

C8H18

• Hydrocarbon: molecular compounds composed only of hydrogen and carbon

Two Types of Chemical Compounds1. ionic: bond between anions (-) and cations (+)

(electrons are donated)nonmetal—metal

2. molecular: (covalently bonded—electrons are shared)

nonmetal—nonmetal3. Metallic: electron “sea” allowing few electrons to

be shared among many atomsmetal—metal

Monatomic Ions• Ions formed from a single atom• Groups 1 and 2 metals lose electrons to form cations• Groups 15, 16, and 17 gain electrons to form anions• Naming cations is very simple: identified by the

element’s nameK+ potassium cationMg2+ magnesium cation

• Naming anions: drop the ending to the element’s name and add –ium

O2- oxideCl- chloride

Transition metals have variable

charges!!!

Stock SystemWhen naming ionic compounds and an element has multiple possible charges, the charge is given in roman numerals in () after the name of the metal

Fe2+ iron (II)Fe3+ iron (III)

Naming a binary ionic compound according to the stock system illustrated below.

CuCl2

Binary Ionic Compounds• Binary compounds: compounds composed of two

elements• The total number of positives and negatives must

be equal, resulting in an overall neutral chargeNa Cl Mg Br2

Writing chemical formulas for binary ionic compounds

“crossing over”: a method of balancing charges between ions in an ionic compound

1. Write the symbols for the ions side by side. Write the cation (+) first!

2. Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion

3. Check to make sure the numbers are in the smallest possible ratio!

Naming Binary Ionic Compounds-The nomenclature, or naming system, of binary ionic compounds involves combining the names of the compound’s positive and negative ions-the cation is ALWAYS written first!!-charges are ONLY given as part of the name if multiple charges are possible

PracticePotassium and iodine

Magnesium and chlorine

Sodium and sulfur

Sulfur and aluminum

Nitrogen and aluminum

More practiceAgCl

ZnO

CaBr2

SrF2

BaO

CaCl2

Compounds containing polyatomic ions• Most polyatomic ions are oxyanions—polyatomic

ions that contain oxygen• Some elements can combine with oxygen to form

more than one type of oxyanionNO2

- nitrite (fewer O atoms) NO3- nitrate

SO32- sulfite (fewer O atoms) SO4

2- sulfate

Sometimes an atom can form more than 2 oxyanions…

Hypochlorite ClO- fewer O than –ite ionChlorite ClO2

-

Chlorate ClO3-

Perchlorate ClO4- one more O than –ate ion

Practice

Sodium iodide

Calcium chloride

Potassium sulfide

Lithium nitrate

Copper (II) sulfate

Sodium carbonate

Calcium nitrite

Potassium perchlorate

PracticeAgO

Ca(OH)2

KClO3

NH4OH

Fe2(CrO4)3

KClO

Naming Binary Molecular CompoundsUnlike ionic compounds, molecular compounds are composed of individually bonded units, or moleculesTwo Systems:1. Prefixes (“Old system”)2. Stock system (uses oxidation numbers)

NONMETAL—NONMETAL

ExamplesCCl4 carbon tetrachloride (tetra: prefix for 4)

CO2 carbon dioxide (di: prefix for 2)

P4O10 tetraphosphorus decoxide (deca: prefix for 10)

PrefixesNumber Prefix 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-

Binary Compounds of N and ON2O dinitrogen monoxide

NO nitrogen monoxideNO2 nitrogen dioxide

N2O3 dinitrogen trioxide

N2O4 dinitrogen tetraoxide

N2O5 dinitrogen pentoxide

No prefix is used for the first atom if it is a single atom

PracticeSO3

ICl3

PBr5

Carbon tetraiodide

Phosphorus trichloride

Dinitrogen trioxide