News!
Match up
the
formulae
Formulae of compounds
Learning aims:
Recognise common formulae
Carry out flame tests
1
Formulas of elements and
molecules
• Individual elements are usually written as
A compound
when
single atoms
e.g. Na, is
Mg,
C, S, Fe
more than
one are written as
• A few non-metallic
elements
element
is chemically
molecules
containing
two atoms:
bonded
to another
• Hydrogen
H2
element
• Fluorine F2 etc.
• It is important to be able to recognise
common formulae
2
Some common compounds
name
formula
atoms present
HCl
1 H + 1 Cl
sulphuric acid
H2SO4
2H+1S+4O
nitric acid
HNO3
1H+1N+3O
sodium hydroxide
NaOH
1 Na + 1 O + 1 H
KOH
1K+1O+1H
carbon monoxide
CO
1C+1O
carbon dioxide
CO2
1C+2O
ammonia
NH3
1 N + 3H
nitrogen dioxide
NO2
1N+2O
sulphur dioxide
SO2
1S+2O
sulphur trioxide
SO3
1S+3O
hydrochloric acid
potassium hydroxide
3
Have a read!
The valency is the
combining power
of an element
A positive valency
ion or atom, will
combine with a
negatively charged
one
Take a few minutes to
read pages 2 and 3 of
your worksheet to
look at common
valencies of ions
Think of the
positive charged
valencies as the
first name, and the
negatively charged
as the surname,
when naming a
compound.
4
How do we go about writing
the formula
•
•
•
•
•
•
Write down the symbols from the table
List the valency below each
Cross them over
Cancel them down if possible
Write the formulae
Let’s work through some examples…
5
Formula of compounds
sodium oxide
symbols
Na
O
valency
1
2
formula
Na2O
6
Formula of compounds
lithium nitrate
symbols
Li
NO3
valency
1
1
formula
LiNO3
7
Formula of compounds
copper(II) nitrate
symbols
Cu
NO3
valency
2
1
formula
Cu(NO3)2
8
Formula of compounds
chromium(III) oxide
symbols
Cr
O
valency
3
2
formula
Cr2O3
9
Formula of compounds
ammonium sulphate
symbols
NH4
SO4
valency
1
2
formula
(NH4)2SO4
10
Formula of compounds
iron(II) hydroxide
symbols
Fe
OH
valency
2
1
formula
Fe(OH)2
11
Formula of compounds 1
Nickel(II) iodate(V)
Ni(IO3)2
Magnesium carbonate
MgCO3
Potassium hydrogencarbonate
KHCO3
Copper(II) sulphate
CuSO4
Magnesium nitride
Mg3N2
Zinc iodide
ZnI2
Formula of compounds 2
Barium sulphite
BaSO3
Lead(II) sulphate
MgSO4
Sodium hydrogensulphate
NaHSO4
Aluminium chloride
AlCl3
Chromium(III) nitrate
Cr(NO3)3
Iron(II) bromide
FeBr2
13
Formula of compounds 3
Silicon chloride
SiCl4
Ammonium phosphate
(NH4)3PO4
Silver dichromate(VI)
Ag2Cr2O7
Iron(III) oxide
Fe2O3
Sodium nitrite
NaNO2
Potassium manganate(VII) KMnO4
14
Break
15
Qualitative analysis
Qualitative analysis is a method of
analysis that tells us whether a
substance is present or not.
It does not tell us how much of
something is there, so no numerical
values
Qualitative analysis of metal ions – flame
tests
Qualitative analysis of salts
16
Flame tests
• When metals or salts containing those
metals are heated in a flame characteristic
colours are produced. This is used to
identify certain metals.
17
Demo!
18
Flame tests

Safety First: Wear safety goggles

Stand up

Tuck your chair & bags under your desk

Tie back long hair
19
Formulae of compounds
Learning aims:
Recognise common formulae
Carry out flame tests
20