1
Yr 9
Name: ______________________
NAMING AND WRITING CHEMICAL FORMULAE – Worksheet
IONIC BONDING
Simple ions:
These consist of single atoms that have either lost or gained electrons.
If the atom loses electrons it becomes positive (groups 1 – 3).
If the atom gains electrons it becomes negative (groups 5 – 7).
From the periodic table:
Valency
Group
+1
I
H
Li
Na
K
Usually +2
(but can vary)
+3
III
4
IV
-3
V
-2
VI
-1
VII
Transition metals
B
Al
Ga
C
Si
Ge
N
P
As
O
S
Se
F
Cl
Br
+2
II
Be
Mg
Ca
Write the ions of these elements:
Sulphur
Hydrogen
Carbon
Bromine
Sodium
Nitrogen
Lithium
Chlorine
Fluorine
Potassium
Iodine
Copper
Calcium
Phosphorus
Beryllium
Zinc
Magnesium
Boron
Oxygen
Helium
0
VIII
He
Ne
Ar
Kr
Compound ions (polyatomic ions):
These consist of more than one atom and the valency is equal to the charge on that ion:
Formula
PO43SO42CO32NO3MnO4OHHCO3NH4+
Name
Phosphate ion
Sulphate ion
Carbonate ion
Nitrate ion
Permanganate ion
Hydroxide ion
Bicarbonate / hydrogen carbonate ion
Ammonium ion
Valency
3
2
2
1
1
1
1
+1
Writing formulae:
A compound is represented by a formula, which is determined from the valencies of the elements involved. The
following simple rules apply:
1.
The symbol of the positive ion is written down first; this is followed by the symbol for the negative ion.
2.
No charge is written in the final formula.
3.
Where more than one compound ion is found in a formula, brackets are placed around the compound ion
and the appropriate number is written outside the brackets (eg: Mg(NO 3)2 )
NB:
The formula for an ionic compound is not a molecular formula, since
ions don’t form molecules. Instead they form large crystal lattices and
the formula shows the ratio of the ions in the crystal eg NaCl (sodium
chloride, commonly known as table salt).
2
Rules:
1.
Write down the symbols of the elements
Example:
H
S
2.
Write the valency of each element above each symbol
+1
H
2
S
3.
Simplify the figures if possible (eg 2 & 4  1 & 2)
4.
Cross each valency over to the bottom of the other element
+1
H
2
2
S
1
5.
Write down the completed formula (the signs disappear)
H2S
Complete the following table by writing the correct formula in each box:
Cl-
F-
I-
O2-
S2-
N3-
Li+
Na+
K+
Be2+
Mg2+
Ca2+
Al3+
Complete the following table. Refer to the table of compound ions on page 1.
NAME
FORMULA
NAME
Magnesium chloride
Zinc fluoride
Potassium bromide
Sodium sulphide
Lithium hydroxide
Calcium nitrate
Calcium carbonate
Sodium hydrogen carbonate
Ammonium hydroxide
Hydrogen bromide
Aluminium oxide
Barium sulphate
FORMULA
3
Naming compounds:
The names of compounds are obtained by simply adding the names of the two ions – first the cation, then the
anion.
1.
Binary compounds are those having only two kinds of atoms. These names usually end in -ide.
Eg:
MgCl2
magnesium chloride
Li2O
lithium oxide
2.
Compounds having polyatomic ions take on the names of the ions involved:
Eg:
Na2SO4
sodium sulphate
NH4NO3
ammonium nitrate
Write the names of the following compounds:
No of each
NAME
FORMULA
element
1
Na, 1 Cl
NaCl
NAME
FORMULA
No of each
element
Mg(OH)2
CuO
FeCl3
K2CO3
FeO
CuSO4
HF
ZnCl2
MnO2
NaHCO3
Na2SO4
KHCO3
MgF2
NaNO3
PbBr2
Mg(NO3)2
AgNO3
COVALENT BONDING
Occurs between non-metal atoms. Electrons are shared and molecules are formed. A molecule is formed from the
smallest number of atoms that can exist bonded together in a stable form. A diatomic molecule consists of two
non-metal atoms covalently bonded together eg. H2, O2.
Sometimes for covalent molecules we use prefixes in a name, to indicate how many atoms of a particular element
are found. The prefixes are:
Mono – 1
Di
–2
Tri
–3
Tetra – 4
Complete the following table:
NAME
FORMULA
NAME
Carbon dioxide
Carbon monoxide
Sulphur dioxide
Nitrogen dioxide
FORMULA
SO3
NO
CCl4
H2O