The 3 Basic Particles of Atomic Structure

Atoms are built from tiny particles called protons, neutrons and electrons but what are thy like and where do you find them in an atom?


Chemicals are built from atoms and atoms usually behave in predictable ways but to understand how they can do this and why it is so predictable, you need to know about atomic structure first.

1. Protons

Protons are positively charged particles which form part of the nucleus of an atom. Their mass is incredibly small, to write down the actual number is pointless as it is impossible for the human mind to grasp their scale. We therefore use a scale that we can understand and say that a proton has a mass of 1 atomic mass unit (amu). That way, we can at least compare these particles to the neutron and electon.

On the periodic table, the elements are arranged in order of atomic number. The atomic number tells you how many protons there are in the nucleus. Every atom of a particular element contains the same number of protons. Take carbon as an example, it has an atomic number of 6 so every carbon atom in the universe will have 6 protons.

The atomic number can also be referred to as the proton number.

2. Neutrons

Neutrons have the same mass as protons i.e. 1 atomic mass unit, but have no electrical charge. Neutrons are neutral. Together with protons, they are part of the nucleus which makes up pretty much all of the mass of an atom. When you count up the total number of protons and neutrons in the nucleus, the result is called the atomic mass number.

Unlike protons, the atoms of an element can contain different numbers of neutrons so using carbon as an example, we find that the majority of carbon atoms contain 6 neutrons but we also find that a few contain 7 and a few contain 8. These variations on the ‘common’ carbon atoms are called isotopes.

Why do you think that we call these isotopes carbon-12, carbon-13 and carbon-14? Hint: add the number of protons and neutrons together.

Atomic structure - protons, neutrons and electrons.

[Image – Julian Habekost, Jonas Konrad]

3. Electrons

Electrons are 1840 times smaller than protons and neutrons so they are the tiniest of the three particles. They carry the same amount of electrical charge as protons but negative. They orbit the nucleus at a distance in imaginary shells and are held in place by the positive charge of the protons – one proton can hold one electron in place. The result is that an atom in its normal state has exactly the same number of electrons as protons. Going back to our old friend carbon, we know its atomic number is 6 which tells you that it has 6 electrons as well as 6 protons.

And finally …

We mentioned at the start that knowing about atomic structure helps understand how atoms can join together. Chemical reactions take place when atoms exchange or share electrons. Radioactivity happens because certain numbers of neutrons make the nucleus unstable. One weird fact about atoms is that they are mainly empty space so how come they can join together to form some very solid materials? If you study chemistry, physics or both at a higher level, be prepared for protons, neutrons and electrons to become weirder still!

Taught science for 16 years at a secondary school in the East Midlands.