Chemical Formulas
A combination of symbols that represents
the composition of a compound.
NH3 ammonia
Fe2O3 rust
Mass
number
Atomic
number
Na
Electric
charge
No. of
atoms
He:
H∙
Na∙ Mg:
:P:
:S: :Cl: ..
:Si:
.
∙Al:
..
:Ar:
.
..
K∙
Rb∙
Cs∙
Fr∙
Ca: Sc:
:
Li∙ Be:
.. ..
:N:
∙B: :C: . :O: :F: :Ne:
..
..
:Kr:
..
..
:Xe:
..
..
:Rn:
..
Challenge
Look at the following chemical formulas
and try to figure out a rule for bonding.
Use what you have learned about
electrons and stability to help.
CaCl2
Al2O3
K2S
NaCl
AlF3
H2O
MgBr2
MgO
SrF2

Hint- draw the elements’ dot notation.
Formation of an ionic bond
g
electron jumps from Na to Cl
electron acceptor (Cl)
meets
electron donor (Na)
ions attract
to form
neutral pair

structure: smallest building blocks are ions- not
molecules!

large numbers of ions can attract to form
clusters and eventually crystals
an ion pair
an ion cluster
a crystal
lattice
Ions



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Cations- positive ions (lose electrons)
ex.: Na+ Ca2+ Al3+
Anions- negative ions (gain electrons)
ex.: Cl- O2Polyatomic ions- ions made of more than
one atom.
ex.: NO3- SO42- PO43The most frequently occurring version of a
polyatomic ion got the name -ate.
Oxidation Number
The number of electrons gained, lost, or
shared in compound formation.
Alkali metals: 1+
Alkali earth metals: 2+
Halogens: 1Oxygen group: 2-
How would calcium and chlorine
combine?
CaCl2
Cl
Ca
Cl
The net charge of a compound
should be zero.
The total positive charges must equal the
total negative charges.
How can Na+ combine with O2- to form a
neutral compound?
You need 2Na+ to combine with one O2-.
2(1+) + 1(2-) = 0
Write the formulasalways put the cation first
K+ and N3K3N
Ca2+ and N3Ca3N2
Ba2+ and NO3Ba(NO3)2
Criss-cross rule of thumb
Naming binary ionic compounds


Write the cation first
Change the anion ending to –ide
Na+ and Cl- form sodium chloride
H+ and F- form hydrogen fluoride
CaBr2 is calcium bromide
Naming polyatomic ionic
compounds
Simply name the cation and the
polyatomic ion unchanged.
Ex.: NaNO3 is sodium nitrate

Zinc carbonate is ZnCO3
Beware there are two polyatomic ions that end
with –ide. OH- is hydroxide and CN- is cyanide
Molecular Compounds



A molecule is a neutral group of atoms
that are held together by covalent
bonds.
The valence electrons are shared by the
atoms.
Covalent bonding usually occurs between
non-metals. i.e. H2O, CO2, O2, NO
Naming molecular compounds

Use prefixes
1
mono-
2
3
4
5
6
7
8
9
10
ditritetrapentahexaheptaoctanonadeca-
Examples






P4O10 is tetraphosphorus decoxide
N2O3 is dinitrogen trioxide
As2O5 is diarsenic pentoxide
OF2
is oxygen difluoride
- Or use the stock system SO2 is sulfur (IV) oxide
SO3 is sulfur (VI) oxide
Ionic or covalent?
Name







NaBr
CH4
Fe2O3
CO2
CaO
NH4Cl
SiCl4
ionic
Sodium bromide
covalent
Carbon tetrahydride
ionic
Iron oxide
covalent
Carbon dioxide
ionic
Calcium oxide
ionic
Ammonium chloride
covalent
Silicon tetrachloride
Comparing ionic and covalent
compounds
Molecular
compounds
Ionic compounds
smallest
particles
molecules
cations and anions
origin of
bonding
electron sharing
electron transfer
elements
present
close on the periodic table
widely separated on the
periodic table
metallic
elements
present
rarely
usually
electrical
conductivity
poor
good, when melted or
dissolved
state at room
temperature
solid, liquid, or gas
solid
melting and
boiling points
lower
higher
other names
covalent compounds
salts
Diatomic molecules
H2
O2
N2
Cl2
Br2
I2
F2
Empirical Formula


A formula that represents the lowest
integral ratio of atoms of the elements in a
compound.
C2H4, C3H6, C4H8 all have same empirical
formula CH2
Naming acids
anion
acid name
example
-ide
Hydro- ic
HCl hydrochloric acid
-ite
-ous
HNO2 nitrous acid
-ate
-ic
HNO3 nitric acid
Try these






H2SO4
HF
H3PO4
H2SO3
H2CO3
HNO3
sulfuric acid
hydrofluoric acid
phosphoric acid
sulfurous acid
carbonic acid
nitric acid
Calcium bromide
Chromium (III) acetate
Barium sulfate
Copper (I) sulfide
Sulfur hexafluoride
Cr2(C2O4)3
Hg(CN)2
Cu(ClO4)2
ZnC4H4O6
CaBr2
Cr(C2H3O2)3
BaSO4
Cu2S
SF6
Chromium (III) oxalate
Mercury (II) cyanide
Copper (II) perchlorate
Zinc tartrate