Writing Chemical
Formulas
Metals vs Nonmetals
Metals
Nonmetals
Lose electrons (e-)
Form Cations (+ ions)
Gain electrons (e-)
Form Anions ( - ions)
Attracted to Cathode
Attracted to Anode
Positive Ions: Protons # > Electron # = Cation
Negative Ions: Protons# < Electron # = Anion
OXIDATION NUMBER

is the overall charge on an ion after it has lost
electrons (metals) or gained electrons (nonmetals).

When ions are combined together to form
compounds, THE OVERALL CHARGE OF
THE COMPOUND WHICH RESULTS MUST
BE “ZERO” OR NEUTRAL.
Subscripts

Subscript: Small numbers placed to
the lower right of the symbols.
 In chemistry this indicates the
number of atoms of an element.
 When there is only 1 atom of an
element the subscript is not
written.
 Example


SiO3
one silicon atom
three oxygen atoms
Parenthesis

When there is a parenthesis in a
chemical formula the chemicals inside
are multiplied by the number outside.
 Example
Ca(OH2)2
 1-- Calcium atom.
 2 -- Oxygen atoms.
 4 -- Hydrogen atoms.

Coefficients


Coefficient: A large number placed in
front of a chemical formula. This
number indicates how many of each
molecules there are.
Everything in the formula is multiplied
by the number in front.

3MgCO3



3 atoms of Mg
3 of C
9 of O
Writing Chemical Formulas

To write chemical formulas you need to
know:


Which elements are involved
The number of electrons (e-) that elements lose,
gain, or share to become stable
NOTICE:
METAL ION IS ALWAYS WRITTEN FIRST NONMETAL ION IS WRITTEN LAST
SWAP & DROP Method
*When ions are combined to form compounds, THE
OVERALL CHARGE OF THE COMPOUND WHICH
RESULTS MUST BE “ZERO” OR NEUTRAL.
1.
If a the oxidation #s cancel do not swap & drop
Lithium and Fluorine
Li+
Fl= LiFl
2.
If the oxidations #s do not cancel, swap & drop
Aluminum and Oxygen
Al3+
O2= Al2O3
Write a correct formula for the
compound, which would form between.





calcium and sulfur
cesium and oxygen
aluminum and oxygen
sodium and sulfur
potassium an oxygen