1. Atoms: very small
If a helium atom was the size of a full stop, then the average gerbil would be the size of the Earth.

2. Atoms: very small
Now let’s pretend that the helium atom on the right is the size of the Earth.
What’s wrong with this simple picture?

3. How big is a nucleus?
The helium atom is not in the right proportions. The three subatomic particles are wrongly enormous in comparison to the atom’s radius.
If the atom was the size of the Earth, then the nucleus would be about the size of IVC (at the centre of the Earth).

4. Most of the atom is empty space!
If you imagine an atom being the size of Wembley stadium, the nucleus would be about the size of a football on the centre spot.
The electrons would be two peas flying around the whole stadium. The rest of it: emptiness.

5. + - Subatomic particles in more detail Subatomic particle
Relative charge
Relative mass
Common depiction
Proton +1 1
Neutron
Electron -1
1  10-5 + -

6. Li = 7 3 Lithium Number of protons Number of electrons Lithium
No. of protons + neutrons
Mass number
Number of protons
Number of electrons = Li 7
Lithium
Electrons 3
Protons
Neutrons 4 3
Atomic number does not always equal the number of neutrons.
Atomic number or proton number
(No. of protons)

7. = Lithium Number of protons Number of electrons Lithium Electrons 3
Neutrons 4
This is because the atom is neutral. The charges balance out!
-3 charge
+3 charge
No charge
But atoms can gain and lose electrons (they become ions). This changes the overall charge on the atom.

8. Lithium Number of protons “defines” an element – nothing else!
Some isotopes of lithium:
4Li
4-Lithium
3 protons, 1 neutron
6Li
6-Lithium
3 protons, 3 neutrons
10Li
10-Lithium
3 protons, 7 neutrons
11Li
11-Lithium
3 protons, 8 neutrons
Lithium: always 3 protons!
7-Lithium (7Li)
Electrons 3
Protons
Neutrons 4
Atomic number does not always equal the number of neutrons. This can change, even in atoms of the same element. These are called isotopes.

9. Atom P N E How many protons, electrons and neutrons do these have? NaRh
phosphorus
The last of the halogens Xe
The only liquid non-metal
Li+ F-
Carbon-14 (14C)
2 protons 2 electrons 2 neutrons 4 He
A helium atom 2

10. Atom P N E How many protons, electrons and neutrons do these have? Na11 12 Rh 45 58
phosphorus 15 16
The last of the halogens 85
125 Xe 54 77
The only liquid non-metal 35
Li+ 3 4 2 F- 9 10
Carbon-14 (14C) 6 8
2 protons 2 electrons 2 neutrons 4 He
A helium atom 2

11. Electron configuration
Fill in the table
Species
Name
Protons
Neutrons
Electrons
Electron configuration K
Potassium 19 20
2,8,8,1 Ca
Oxygen ion 8
Mg ion in magnesium chloride
Fluoride ion Na
lithium ion in lithium oxide
Halogen ion in LiCl 2+ +

12. Electron configuration
Fill in the table
Species
Name
Protons
Neutrons
Electrons
Electron configuration K
Potassium 19 20
2,8,8,1 Ca
Calcium ion 18
2,8,8 O
Oxygen ion 8 10
2,8 Mg
Mg ion in magnesium chloride 12 F
Fluoride ion 9 Na
Sodium ion 11 Li
lithium ion in lithium oxide 3 4 2 Cl
Halogen ion in LiCl 17 2+ 2- 2+ - + + -