Download ch. 16

What is a
chemical
formula?
Section 16-1
Chemical Formulas
A way of writing the
name of a compound
using chemical symbols.
The chemical formula for
water is H20. Chemical
formulas use subscripts to
indicate how many
atoms of each type of
element are in a
compound. If there is no
subscript, it is assumed to
be 1.
Writing Chemical Formulas
In many
compounds, a
metallic element is
combined with a
non-metallic
element. The symbol
for the metallic
element is written
first. Ex. NaCl,
sodium chloride.
What is an
oxidation
number?
Section 16-2
Electrons
Oxidation Number
Number of electrons an
atom gains, loses, or
shares when it forms a
chemical bond. An
atom which gains
electrons has a
negative oxidation
number, an atom which
loses electrons has a
positive oxidation
number.
Valence Electrons
The electrons in an
atom’s outer energy
level. The first ring can
have 2 and each ring
afterwards can have 8
electrons. If an atom
has 6 valence
electrons, it will have
an oxidation number
of -2. If an atom has 2
valence electrons, it
will have an oxidation
number of +2.
Writing Chemical
Formulas.
You must know
the oxidation
numbers. The
oxidation
numbers of the
elements in a
compound must
add up to 0
(zero).
How are
chemical
compounds
named?
Section 16-3
Binary Compounds
Compounds containing
two elements. NaCl
(sodium chloride) is an
example of a binary
compound. The name
of the element with the
positive oxidation
number is written first
followed by the second
element’s name being
changed to end in –ide.
Some elements
have more than 1
oxidation number.
A Roman numeral
is used to denote
this. Ex. FeCl2 is
iron (II) chloride
and FeCl3 is iron
(III) chloride.
Other Elements
Most elements
have more than 1
oxidation number.
The Roman
numeral in the
name of the
compound shows
the oxidation
number of the
element.
What is a
polyatomic
ion?
Section 16-4
Polyatomic Ions
A group of atoms
that acts as a single
atom when
combining with other
atoms. The group of
atoms is called an
ion because it has
an electrical charge.
The atoms are joined
together by
covalent bonds. Ex.
What are
diatomic
molecules?
Section 16-5
Diatomic Molecules
Molecules made up of
2 atoms of the same
element formed by a
covalent bond. There
are 7. These 7
elements only appear
in nature as a pair of
atoms. So oxygen gas
is always seen as O2.
The other 6 are also
seen as a subscript 2.
What is
formula
mass?
Section 16-6
Formula Mass
The sum of the mass
numbers of all the
atoms in a
molecule. This
number represents
the total of all the
protons and
neutrons. Sometimes
called molecular
mass.
Formula Mass
Steps
1. Write the chemical formula.
2. Find atomic mass of each
element.
3. Multiply the mass number of
each element by its subscript.
4. Add the total masses of all the
elements.
Formula Mass
Ex. Ethyl chloride
C2H5Cl
C = 12
H=1
Cl = 35
2(12) + 5(1) + 1(35)
24+5+35
64 is formula mass.