Intro to Names and Formulas
for Ionic Compounds
November 2, 2015
Chemical Formula
Octane: C8H18
In 1 molecule of octane there are 8 carbon
atoms (C) and 18 hydrogen atoms (H).
Aluminum Sulfate: Al2(SO4)3
In 1 molecule of aluminum sulfate there are 2
aluminum atoms (Al), 3 sulfur atoms (S),
and 12 oxygen (O) atoms.
Ions

All atoms want a full outer shell of
electrons (8 valence electrons)

Atoms will lose or gain electrons in order
to have a full outer shell

Atoms that lose electrons are cations

Atoms that gain electrons are anions
Monatomic Ions
Group #1 elements form +1 ions, Ex) Li+, Na+1
Group #2 elements form +2 ions, Ex) Ca+2, Mg2+
Aluminum forms +3 ions
Nitrogen and phosphorus form -3 ions
Oxygen and sulfur form -2 ions
The halogens, F, Cl, Br, I, form -1 ions
Transition metals can form multiple ions: Ex) Fe+3 and Fe+2
Naming Monatomic Ions
Cations are identified by element’s name
Ex) Li+ lithium
Ex) Ca+2 calcium
Anions-ending of element’s name is replaced
by ide
Ex) F- fluoride
Ex) O-2 oxide
Writing Names and Formulas for Ionic
Compounds (Ionic =metal and nonmetal)
Ex 1) Aluminum and Oxygen
Ex 2) Magnesium and Bromine
Ex 3) Copper and Bromine
(Copper has +2 charge)
Ex 4) Chromium and Fluorine
(Chromium has +3 charge)
Compounds with Polyatomic
Ions
See table on p 226 (I will give you a list of
polyatomic ions you need to memorize)
Ex 1) Calcium and Hydroxide
(Hydroxide is polyatomic ion:
OH-)
Name: calcium hydroxide
Formula Ca(OH)2
Practice

Write the names of the following compounds:

1) CaCl2

2) BaO2

3) KCl

4) K2O