Download Chemical Formulas

Chemical Formulas
A combination of
symbols
representing
chemical substances
Chemical Formulas
Examples
NaCl –
1 sodium atom
1 chlorine atom
Chemical Formulas
NaHCO3 –
1 sodium
1 hydrogen
1 carbon
3 oxygen
Chemical Formulas
Shows the type and
number of atoms
Chemical Formulas
C12H22O11
C - Carbon – 12
H - Hydrogen – 22
O – Oxygen - 11
Chemical Formulas
Subscript
Small lowered number
showing the number of
atoms of the elements in
the compound
Chemical Formulas
Subscript
Subscripts never
change
Subscript of one is not
written, it’s understood
Chemical Formulas
Parentheses
Encloses a group of
atoms
The subscript indicates
the number of groups
Chemical Formulas
Parentheses
The number of each
atom in the parentheses
is multiplied by the
subscript outside the
parentheses
Chemical Formulas
Parentheses
Example Ca(OH)2
Ca-calcium-1
O-oxygen-1x2=2
H-hydrogen-1x2=2
Chemical Formulas
Parentheses
Example Al2(SO4)3
Al-aluminum-2
S-sulfur-1x3=3
O-oxygen-4x3=12
Molecular Mass
The sum of the
atomic mass of all of
the atoms in a
molecule
To find molecular mass
 1. write the chemical formula
for the compound
 2. count the number of atoms of
each element in the compound
 3. look up the atomic mass of
each element, round off to 2
decimal places.
Molecular Mass
4. multiply the atomic
mass of each element by
the number of atoms of
that element in the
compound.
5. add the total mass
Molecular Mass
Examples CaCl2
Ca-1 x 40.08 = 40.08
Cl- 2 x 35.45 = 70.9

110.98 amu
Molecular Mass
Example Ba(NO3)2
Ba:1x137.33 =137.33
N:1x2=2x14.01= 28.02
O:3x2=6x16.00= 96.00
Molecular Mass
Example Ba(NO3)2
Ba 137.33
N +28.02
O +96.00

261.35 amu
Quiz – find the molecular weight:
O2
CO2
Ca(OH) 2
H2O
Al2O3
Binary Compound
A compound composed of
two types of elements
The element whose
symbol appears first on
the formula also appears
Binary Compound
When there is a metal and a
nonmetal…
The metal appears first in
both the formula and the
name
Binary Compound
The name of the
second element
follows but with its
ending changed to ide
Binary Compound
Fluorine – fluoride
Chlorine – chloride
Bromine – bromide
Iodine - iodide
Binary Compound
Oxygen – oxide
Nitrogen – nitride
Phosphorus phosphide
Binary Compound
Examples LiCl
Lithium
Chlorine  chloride
Lithium chloride
Binary Compound
Examples NaF
Sodium
fluorine  fluoride
Sodium fluoride
Binary Compound
Examples BaO
Barium
Oxygen  oxide
Barium oxide
Binary Compound
Examples AlBr3
Aluminum
Bromine  bromide
Aluminum bromide
Binary Compound
Examples Cr2O3
Chromium
Oxygen  oxide
Chromium oxide
Binary Compound
When the compound
is made up of two
nonmetals, prefixes
are used
Binary Compound
Prefixes
Mono – 1
Di – 2
Tri - 3
Binary Compound
Prefixes
Tetra – 4
Penta – 5
Hexa – 6
Sept - 7
Binary Compound
The first element only
uses a prefix when there
are two or more atoms
The second element
always uses a prefix and
the suffix -ide
Binary Compound
Examples CO2
1 Carbon  Carbon
2 Oxygen  di oxide
Carbon dioxide
Binary Compound
Examples CO
1 Carbon  Carbon
1 Oxygen mono oxide
Carbon monoxide
Binary Compound
Examples N3O5
3 Nitrogens  tri nitrogen
5 oxygens  penta oxide
Trinitrogen pentoxide
Polyatomic ions
A group of elements
that behave like a
single charged atom or
ion
Usually ends in –ite or
-ate
Polyatomic ions
Hydroxide – OH
Chlorate – ClO3
Chlorite – ClO2
Nitrate – NO3
Acetate – C2H3O2
Polyatomic ions
Sulfate – SO4
Phosphate – PO4
Carbonate – CO3
Bicarbonate – HCO3
Ammonium – NH4
Polyatomic ions
Examples Ca(OH)2
Identify the
polyatomic ion CaO
or OH
Polyatomic ions
Examples Ca(OH)2
Calcium
Hydroxide
Calcium hydroxide
Polyatomic ions
Examples Sr(NO3)2
Identify the
polyatomic ion SrN
or NO3
Polyatomic ions
Examples Sr(NO3)2
Strontium
Nitrate
Strontium nitrate
Polyatomic ions
Examples NH4I
Identify the
polyatomic ion NH4
or H4I
Polyatomic ions
Examples NH4I
Ammonium
Iodide
Ammonium iodide
Polyatomic ions
Examples (NH4)2SO4
Polyatomic ions
Examples (NH4)2SO4
There are two
polyatomic ions
Polyatomic ions
Examples (NH4)2SO4
Ammonium sulfate
Polyatomic ions
All compound names
will only have two
names, first and last
Fin…for now
Name these…
 Na2O
 NO
 NaOH
 (NH4) 2O
 K2SO4
 P2O5
 MgCl2
Oxidation numbers
A number that tells
how many electrons
an atom loses, gains
or shares when
forming a compound
Oxidation numbers
The sum of the
oxidation numbers
for the atoms in a
compound is zero
Writing formulas
The symbol of the
element or polyatomic
ion with the positive
oxidation number is
written first
Writing formulas
The symbol of the
element or polyatomic
ion with the negative
oxidation number is
written second
Writing formulas
Cross the oxidation
numbers down to
find the subscripts
Writing formulas
If a polyatomic ion
needs a subscript of 2
or greater, use
parentheses around
the polyatomic ion with
the subscript outside
Writing formulas
Examples
Potassium fluoride
+1
-1
K
F
K1F1 = KF
Writing formulas
Examples
Lithium oxide
+1
-2
Li
O
Li2O1 = Li2O
Writing formulas
Examples
Barium sulfide
+2
-2
Ba
S
Ba2S2 =(reduce) BaS
Writing formulas
Examples
Sodium chlorite
+1
-1
Na ClO2
NaClO2
Writing formulas
Examples
Aluminum iodide
+3
-1
Al I
AlI3
Writing formulas
Examples
Magnesium phosphate
+2
-3
Mg
PO4
Mg3PO4 2 = Mg3(PO4)2
Writing formulas
Examples
Ammonium sulfide
+1
-2
NH4 S
NH4 2 S1 = (NH4)2S
Writing formulas
Examples
Iron(III) nitrate
+3
-1
Fe NO3
Fe1NO3 3=Fe(NO3)3
Writing formulas
Elements with more than
one oxidation number…
Roman numeral is written
in parentheses after the
name of the metal
indicating the oxidation
number
Writing formulas
– copper(I)
+2
Cu – copper(II)
+2
Fe – iron(II)
+3
Fe – iron(III)
+1
Cu
Writing formulas
Example
CuI
1(?) + 1(-1) = 0
Copper(I) iodide
Writing formulas
Example
FeBr3
1(?) + 3(-1) = 0
Iron(III) bromide
Writing formulas
Example
CuO
1(?) + 1(-2) = 0
Copper(II) oxide
Writing formulas
Example
Fe(OH)2
1(?) + 2(-1) = 0
Iron(II) hydroxide
Writing formulas
Example
Cu3(PO4)2
3(?) + 2(-3) = 0
Copper(II) phosphate