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Chemical Formula

a statement in chemical symbols that represents the composition of a substance

symbol in chemical formula

composition (elements)

subscripts in chemical formula

how many of each


composition= H, O
amount= 2,1

2 Types of Chemical Formulas

Empirical and Molecular Formulas

Empirical Formulas

-simplest whole number ratio that elements can combine to form a compound

Molecular Formulas

- the exact number of atoms that are present in each elements for one molecule of a substasnce


- the smallest particle of a substance that can exist and still have the composition and properties of a substance

2 Types of Molecules

Single Atom Molecules & Double Atom Molecules

Single Atom Molecules

- Noble Gases (elements and molecules
ex) Xenon

Double Atom Molecules

- two or more atoms of the same element from a molecule
- 7 Diatomic Elements
ex) Ozone (3 oxygen atoms)

Largest Group

- 2 or more diff. elements chemically combined like H20

Benzene (emp and molecular formula)

C6H6- molecular
CH- empirical

Acetylene (Ethyne)

C2H2- molecular
CH- empirical


H20- molecular
H20- empirical


NH3- molecular
NH3- empirical

2 Types of Compounds

Ionic Compound and Molecular Compound

Ionic Compound


Molecular Compound


when metallic elements combine chemically with non-metallic elements...

one or more elemets is transferred to the non-metal


- 1, 2, 3 valence electrons

metals have a low...

-ionization energy (energy requiered to remove the most loosely held electrons)
- electronegativity (1, 1/2)


1, 5, 6, 7 valence electrons

tend to have high...

ionization energies and electronegativety

rating scate for electronegativety

- ranks atoms ability to attract electrons in this bond
- 0-4 (best electronegatively-- Fluroine)

Ionic Compounds

- transfer electron for a stable octet
- crystal lattice (repeatin pattern in a solid phase)

Ionic Bond

- force of attraction

ex) NaCl

sodium transfers electron to cholorine
(metal to non-metal)

Empirical Formula

1:1 ratio
keeps building

What kind of formuals do ionic coumpounds have?

Empirical Formulas

More ions can join...

as long as the ratio is kept and continued


(+) ion


(-) ion

Rules for writing Binary Ionic Compounds

1) the least electromagnetic element goes first (the metal goes first- cation ion goes first)
2) Assign ionic charges (look at valence structure)
3) Assign enough of each atom so the compound is electrically neutral
# of (+)= # of (-)

what rule should you use?

criss-cross rule

metal, non-metal ends in


Hydrogen (metal/nonmetal)


Ternary Ionic Compounds have...

PAI (poly atomic ions)

possibility types of Ternary Ionic Compounds

a) metal+ and PAI-
b) PAI+ and non-metal (ide)
c) PAI+ and PAI-

when can you drop parenthesis of PAI number?

when the number outside of the parenthesis is 1

never cahnge------ of PAI


oxidation number

state or charge

2 naming systems of ionic compounds of more that one oxidation numner (state)

1) Stock System
2) Latin Root- suffix

Stock System

- oxidation #
- metal ( ) ending

ex) CU+1 chromate

copper (1) chromate
copper(11) chhromate

Latin Root

Latin root- ous (lowest possible charge)
- ic (next lowest)

ex) latin root

cuprous chromate
cuproc chromate

can you reduce within PAI


Backwards Method

To find charge originally

After usign latin root for first too, then you go to the...

stock system

Instead of Hg+1

(hg+2) +2

Cr +2, +3


Cu +1, +2


Fe +2, +3


Sn +2, +4


Pb +2, +4


Sb +3, +5


Hg +1, +2

exists only as 2 (Hg+2)+2

O-1 O-2

O-1 can not be written cause you need 2 of them
peroxide (PAI)

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