Chemical Expressions

Molecular Expressions

• Subscripts – indicate the number of atoms in the formula

- Example

NaC2H3O2

Contains: 1 Sodium atom2 Carbon atoms3 Hydrogen atoms2 Oxygen atoms

Subscripts (cont.)

• Outside parenthesis – apply to all symbols inside the parenthesis

Example:

Al2(SO4)3

Contains: 2 Aluminum atoms

3 x 1 Sulfur atoms

4 x 3 Oxygen atoms

Coefficients

• Represent the number of molecules

- Example6 HCl 6 hydrochloric acid molecules

17 H2O 17 water molecules

Compounds

Combinations of Atoms

Compounds

• All molecules are electrically neutral• Positives combine with negatives

– Positive ions are written first– Negative ions are written last

• All elemental gases are diatomic except the noble gases– H2, N2, O2, F2, Cl2, Br2, I2

• Polyatomic ions – charged groups of atoms which remain intact and combine as a single ion

Determining Chemical Formulas

When determining the chemical formula for a compound one

must consider:

• Valence - Combining Capacity

• Oxidation State – the charge an atom actually has as an ion, or the charge it appears to have when electrons are shared or transferred

Rules for Oxidation State Types Example Oxidation #

Free Elements Na, He, C 0

Hydrogen H+ 1+ except in metal hydrides LiH

Oxygen O2- 2- except in peroxide 1-

1A Alkali Metals Na+ 1+

2A Alkali Earth Ca2+ 2+

Rules for Oxidation State (cont.)Types Example Oxidation #

7A or 17 Halogens F- 1- only when written last

Monatomic ions Cu2+, Na+ assigned oxidation # according to the rule that the sum of the ox. # in a cpd. = 0

Polyatomic ions SO42- the sum of the ox. # must

equal the charge on the ion

Naming Compounds(Nomenclature)

• Binary Compounds – compounds composed of only two kinds

of atoms

• Salts – composed of metal (cation) and a nonmetal (anion)

Binary Names

Metal + Nonmetal- name the metal

- use the stem name of the

nonmetal with an “ide” ending

- insert roman numeral when there is

more than one oxidation state for the

metal

Example 1:

Potassium combines with Sulfur

Ions: K+ S2-

Formula: K2S

Name: Potassium Sulfide

Example 2:

Zinc combines with Chlorine

Ions: Zn2+ Cl-

Formula: ZnCl2

Name: Zinc Chloride

Example 3:

Copper combines with Oxygen

Ions: Cu+ or Cu2+ O2-

Formula: Cu2O or CuO depends on the

oxidation # of the Cu ion

Name: Copper (I) Oxide or Copper (II) Oxide

Now You Try It!

• Zirconium with Iodine

Formula: ??

Name: ??

• Cr 6+ with Sulfur

Formula: ??

Name: ??

Determine the formula and the names for the following compounds

Binary Names (cont.)Nonmetal + Nonmetal

- name the cation first- name the anion with an “ide” ending - use prefixes to number the atoms when necessary

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

Example 4:

Carbon combines with Oxygen

Ions: C+4 02-

Formula: CO2

Name: Carbon Dioxide

Example 5:

Phosphorous combines with Oxygen

Ions: P+5 O2-

Formula: P2O5

Name: Diphosphorous pentoxide

Note: There are other combinations for these two elements

Practice!!!

• Nitrogen 4+ with Oxygen

Formula: ??

Name: ??

• Phosphorous 3+ Bromine

Formula: ??

Name: ??

Determine the formula and the names for the following compounds

Answer!!!

• Nitrogen 4+ with Oxygen

Formula: NO2

Name: Nitrogen

dioxide

• Phosphorous 3+ with Bromine

Formula: PBr3

Name: Phosphorous tribromide

Ternary Compounds

• Compounds containing with 3 kinds of atoms

• Consist of a metal and a polyatomic ion

• Name metal first (with roman numeral if needed)

• Name polyatomic ion

Other Polyatomic Ions

“per”__”ate” “ate” + 1 oxygen

“ate” suffix ion sheet **

“ite” suffix “ate” – 1 oxygen

“hypo”__”ite” “ate” – 2 oxygens

“ide” suffix hydroxidecyanideferricyanide

Example 6:

Sodium combines with Carbonate

Ions: Na+ CO32-

Formula: Na2CO3

Name: Sodium Carbonate

Example 7:

Aluminum combines with Phosphite

Ions: Al3+ PO33-

Formula: AlPO3

Name: Aluminum Phosphite

Now you try it!!

Barium combines with Nitrate

–Formula ??

–Name ??

Try another one!!

Lead combines with Sulfite (give all possible answers)

Formulas –

Names -

Naming Acids

• Acids are compounds containing H+ ions

• Negative ions that end in “ate”– ___________ic acid

• Negative ions that end in “ite”– ___________ ous acid

• When no oxygen in the formula– hydro ___________ic acid

Example 8:

Hydrogen combines with Sulfate

Ions: H+ SO42-

Formula: H2SO4

Name: Sulfuric Acid

Practice!!

• Name this acid

HCl

Practice!!

• Name this acid

HCl

hydrochloric acid

Naming Bases

• Bases are compounds containing OH- ions

• Name the metal first followed by the word hydroxide

Example: Ba(OH)2 Barium hydroxide

An Older Naming Method

• Traditionally Latin names were used for the metals

• If the metal was in the higher oxidation state the suffix ‘ic’ was used on the latin root for the metal

• If the metal was in the lower oxidation state the suffix ‘ous’ was used on the latin root for the metal

A Few Latin Names

Fe Ferrum Fe3+ ferric

Fe2+ ferrous

Cu Cupurum Cu2+ cupric

Cu+ cuprous

Pb Plumbum Pb4+ plumbic

Pb2+ plumbous

Examples:

FeCl3 Ferric Chloride

PbO Plumbous Oxide

CuSO4 Cupric Sulfate