2. Inside the nucleus page 6
Structure of atom - interactive graphic
Picture 2.1 A model of the atom with electrons on the edge and a central nucleus made of protons and neutrons.
Mass and charge
Atoms have a tiny central nucleus with electrons whizzing around outside it. The electrons are fundamental particles. However, the nucleus is made from collections of two smaller particles: protons and neutrons.

What are protons and neutrons?
The protons and neutrons lie in the tiny nucleus. They have very similar masses, but the proton has a positive charge whereas the neutron is not charged (hence the name neutron – neutral). The neutron helps keep the nucleus together.

The electron has a negative charge and very little mass (1800 times less than protons and neutrons).


proton 1 +1
neutron 1 0
electron 1/1800 -1
Table 1. Relative masses and charges of the particles in an atom.
The nucleus
Most of the mass of the atom is in the nucleus. However, despite carrying most of the atom’s mass, the diameter of the nucleus is 100,000 times smaller than the diameter of the atom. This means the nucleus is incredibly dense (as if the whole Earth were squashed into a football stadium).

navigation bar
Question 5
Look at the table below. It shows information about the particles in an atom (units are relative). Some of the cells are blank. Fill in the blanks using the drop down menus.
particle where is it? charge mass
electron 1/1800
proton +1
neutron inside the nucleus