Wait a minute - where are the neutrons ?
We know that opposite charges attract each other, but the converse is also true - the same charges repel each other. When there is just one proton in the nucleus (like the Hydrogen we just looked at), there isn't a problem, but if we had two protons in the nucleus, lying side by side, they would repel each other. They need something to keep them apart. Enter the neutron. If we draw another element, with two protons in the nucleus, we have a different element - Helium.

It is the number of protons in an atom that determines which element it is.

Because Helium has 2 protons, it needs 2 electrons to be charge neutral (2 positives need 2 negatives). Also notice that Helium has 2 neutrons in the nucleus to keep the positive protons from repelling each other and breaking the atom apart. Because neutrons do not have a charge, they do not affect the overall charge of the atom.

We could carry on drawing bigger atoms with increasing numbers of protons, neutrons, and electrons. If we did this, we would draw the elements described in the table below :


Protons
Neutrons
Electrons
Element Name
1
0
1
Hydrogen
2
2
2
Helium
3
4
3
Lithium
4
5
4
Beryllium
5
6
5
Boron
6
6
6
Carbon
7
7
7
Nitrogen
8
8
8
Oxygen
9
10
9
Flourine