AQA Specification
GCSE Chemistry
Unit 1: Chemistry 1
C1.1 Fundamental ideas in
chemistry
C1.1.1 Atoms
The Atom
An atom consists of three main particles
Nucleus
Protons, which are positively charged
Neutrons, which have no charge
Electrons, which are negatively charged
The Atom
orbital
The electrons constantly fly around the nucleus
The orbital shows us where we are most
likely to find the electrons at any given
moment in time
The Atom
The electrical charge of each particle can be written in a
‘relative electrical charge’ table
Name of particle
Charge
Proton
+1 (positive)
Neutron
0 (neutral)
Electron
-1 (negative)
Elements
carbon
6 protons
6 neutrons
6 electrons
Atoms can have different numbers of particles
If an atom has six protons, six neutrons
and six electrons, it is a carbon atom.
Carbon is an element
Elements
oxygen
8 protons
8 neutrons
8 electrons
If we add two more of each particle…
Two more protons
This is an oxygen atom
Two more neutrons
Oxygen is a different
Two more electrons
element to carbon
Elements
sodium
11 protons
12 neutrons
11 electrons
If we add even more particles…
Three more protons
This is a sodium atom
Four more neutrons
Sodium is a different element
Three more electrons
to carbon and oxygen
Particles
So the three particles which make up an atom are the
protons, electrons and neutrons
The number of protons is always the same as the
number of electrons in an atom
Particles
carbon
+ 6+protons
+ + + +
–6 –
electrons
– – – –
oxygen
8 protons
8 electrons
sodium
11 protons
11 electrons
Sodium has
Carbon
Oxygen
has
hassix
eleven
eight
protons
protons
protons
in the
ininthe
nucleus,
thenucleus,
nucleus,
therefore
therefore
therefore
it has
itithas
has
six
electrons
eight
eleven
electrons
electrons
flyingflying
around
flying
around
around
the outside
the
the
outside
outside
Electrons are negative, and protons and positive. If
you have the same number of positive and negative
particles, you have no overall charge
So we can say that atoms have no overall electric
charge
Orbitals
1st orbital
2nd orbital
3rd orbital
You may have noticed some atoms have more orbitals
Each orbital can only hold a certain number of electrons
The first orbital can hold up to 2.
The second can hold up to 8. The third can also hold up to 8.
Orbitals
1st orbital
2nd orbital
3rd orbital
So the more electrons an atom contains, the more orbitals
it needs to house them all
Orbitals can also be known as shells or energy levels
Drawing elements
If you are asked to draw an element, firstly you need to
find out how many electrons it has. Let’s take sodium for
example
We know it has 11 electrons in its orbitals
Drawing elements
When you draw elements yourself you won’t need to
draw the protons and neutrons, so the nucleus can be
drawn as a circle in the centre
Then you need to draw the orbitals. Don’t forget how
many electrons can fit on each one. 2, 8, 8
Drawing elements
XX
XX
XX
XX
You can draw
electrons as a
cross and it’s
also best to
draw them in
pairs
XX
For sodium you need a total of 11 electrons.
That means two on the first shell
Eight on the second shell
And just one on the third shell: 2+8+1 = 11
Drawing elements
XX
XX
XX
XX
XX
XX
XX
carbon
oxygen
So, carbon would be drawn like this, with six electrons
And oxygen like this, with eight electrons
Drawing elements
carbon
2, 4
There are two
electrons on
the first
energy level
andoxygen
four on
2, 6
the second
energy level
sodium
2, 8, 1
In addition to drawing the elements you could also
describe the electronic structure underneath by saying
how many electrons there are on each energy level
Element names
There are around 100 known elements in the universe and
each one is represented by a ‘chemical symbol’
The chemical symbol is made up of one, two or sometimes
three letters.
The first letter is always a capital, and any other letters are
written in lowercase
Element names
carbon
oxygen
sodium
C
O
Na
The chemical symbols come from the Latin word for the
element. Sometimes the Latin word is similar to the English
word so you can easily guess the element.
Carbon is ‘C’ and oxygen is ‘O’
However, if we look at sodium, the Latin word for this
element is ‘natrium’ so the chemical symbol is ‘Na’