Element and compounds
By the end of this session you should be able
to....
1) Explain what element symbols, chemical formulae
and equations tell us
2) Describe the structure of an atom, and calculate
the number of protons, electrons and neutrons in
an element.
3) Understand the basis of chemical equations and
how to balance them
Element symbols
Chemical formulae
Elements are combined to make
compounds with specific combinations
Sodium Chloride Calcium carbonate
NaCl
CaCO3
Oxygen
O2
Copper sulphate
CuSO4.5H2O
Are these atoms, molecules, elements or compounds?
Term
Definition
Example
Atom
The smallest part of a
substance that cannot be
broken down by chemical
means
Sodium, Na
Molecule
Two or more atoms joined
together
A substance that cannot be
broken down
Oxygen O2
Element
Compound
Oxygen O2
Sodium, Na
A substance made up of two Glucose C6H12O6
or more elements
Table salt – Sodium
chemically joined together chloride (NaCl)
Which is the odd one out and why?
Calcium
Chlorine
Carbon dioxide
Atomic Structure
500 BC
1800
1900
2000
Relative size and charge of sub atomic
particles
Particle
Size
Charge
Proton
1
+1
Neutron
1
0
Electron
1/1840
-1
In any atom, the number of protons and electrons is equal
so that the atom has a neutral electrical charge overall.
Every element has a distinct number of protons,
electrons and neutrons.
Atomic mass
= protons + neutrons
Atomic (proton) number
= protons = electrons
7
Li
3
Task: Calculate the number of protons, electrons and
neutrons in the following elements:
Element
Atomic
number
Atomic
mass
Lithium
3
7
Nitrogen
7
14
Chlorine 35
17
35
Chlorine 36
17
36
Lead
82
207
Protons
Electrons
Neutrons
Chemical equations
Chemical equations show us what happens when
different substances react together.
Reactants
→
Products
What ever atoms are on the left must be
present on the right, just in a different
combination.
For example,
Carbon + oxygen → carbon dioxide
C (s) +
O2
(g)
→
CO2 (g)
Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
Sodium + water → sodium hydroxide +
hydrogen
2 Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2 (g)
Na
H
O
Can you.....
1) State the combination of elements in
iron hydroxide – Fe(OH)3?
2) Explain the difference between an
atom and molecule?
3) Explain the key steps to balancing an
equation?