Chapter 7 – Chemical Formulas and Chemical Compounds

7-1 Chemical Names and Formulas What’s so important about a chemical

formula?It indicates the relative # of atoms of

each kind in a chemical compoundMolecular Compound: chemical

formula reveals the # of atoms in a single molecule. C8H18

Ionic Compound: consists of a lattice of positive and negative ions held together by mutual attraction. Simplest ratio NaCl

Al2(SO4)3- How many atoms are there?

AlSO

2312

Monoatomic Ions

Ions formed from a single atom Ex. Na Na1+ , O O2-

Not all main-group elements form ions, C and Si form covalent bonds instead of ionic bonds

Sn and Pb are exceptions lose only 2 e-s instead of 4 or sometimes they keep all 4 electrons.

Naming Monoatomic Ions

Cations are identified by the elements name

Anions the ending of the element’s name is dropped. The ending –ide is added.Ex. Fluorine (F) = Fluoride ion (F-)Nitrogen (N) = Nitride (N3-)Flash Cards may be useful to

memorize these!!!!

Binary Ionic Compounds

Compounds composed of two different elements.

Ex. Magnesium and Bromine form Magnesium Bromide, MgBr2

Rules for Ionic Compounds

1. Write the symbols for the ions side by side. The cations go first. Al 3+ O 2-

2. Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion. Al2O3

3. Check subscript and divide them by their largest common factor to give the smallest possible whole-number ration.

4. Write the formula

Write the formula for the following:

Magnesium and iodine Potassium and sulfur Aluminum and chlorine Zinc and bromine Cesium and sulfur Strontium and oxygen Calcium and nitrogen

MgI2

K2S

AlCl3 ZnBr2

Cs2S SrO Ca3N2

Name the following:

BaF2

CaO AgF CdO K3N NaI AlBr3

Barium Fluoride Calcium Oxide Silver Fluoride Cadmium Oxide Potassium Nitride Sodium Iodide Aluminum Bromide

The Stock System of Nomenclature

Some elements form two or more ions such as Fe, with different charges.

This system uses Roman numerals to indicate an ions’ charge

Fe 2+ or Fe 3+ FeCl2 = iron (II) chloride

FeCl3 = iron (III) chloride

Write the formula and give the name for the following: Cu + and O 2-

Fe 3+ and S 2- Cu 2+ and Cl -

Sn 2+ and Cl -

Hg 2+ and O 2- Sn4+ and S 2- V 2+ and F -

V 4+ and Br -

Name the following:

CoI2

HgI2

PbS2

CuBr2

Compounds Containing Polyatomic ions

Oxyanions- polyatomic ions containing oxygen

Nitrate vs. Nitrite – (-ite less oxygen)NO3

- and NO2-

Sulfates, Nitrate, Chlorates

Write the formulas for:

Copper(II) nitrate Potassium iodide Sodium hydroxide Ammonium acetate Calcium carbonate Potassium permanganate Sodium sulfate Iron(III) nitrate

Name the following:

Ag2S NaMnO4

Ba(OH)2

NH4NO3

Fe(ClO)2

Ca(NO3)2

K2SO3

NaCH3COO

Naming Binary Molecular Compounds # 1 2 3 4 5 6 7 8 9 10

# Mono Di Tri Tetra Penta Hexa Hepta Octa Nona deca

Rules for Molecular Compounds 1. The least electronegative element

is first. It is given a prefix if it is more than one

2. the second element is named by combining a prefix, the root of the word, and –ide ending

3. the o or a at the end of the prfix is usually dropped when the word following begins with another vowel.

Examples.

As2O5 = diarsenic pentoxide PF5 = phosphorus pentafluoride XeF4 = Xenon tetrafluoride CCl4 = carbon tetrachloride Carbon dioxide = CO2

Dinitrogen pentoxide = N2O5

Sulfur hexafluoride = SF6

Dinitrogen monoxide = N2O

Acids and Salts

Acids can be binary acids or oxyacids Binary acids are acids that consist of

H and a halogen, HCl hydrochloric acid

Oxyacids, contain H, P and a third element, Sulfuric Acid, H2S

Pg 214