Atomic structure

Important Definitions:

Atom The unit particle of an element
Proton Number The number of protons in one atom of an element
Nucleon Number The number of protons and neutrons in an atom of an element
Isotopes Atoms of the same element, that have different number of neutrons


The Atom

An atom is the simplest unit of an element. It consists of:

  • A nucleus : containing protons and neutrons
  • Several electrons orbiting the nucleus, arranged in energy levels or shells
Particle Relative mass Relative charge
Proton 1 Positive (+1)
Electron 1/1840 Negative (-1)
Neutron 1 No charge

Every atom has equal number of protons and electrons; hence the atom has no overall charge!

Structure of an atom

<Image for labelled structure of an atom here>


Isotopes are atoms with different nucleon numbers of the same element.

To make that a little simple, isotopes are atoms with same number of protons, and different number of neutrons.

Isotopes are usually written in the following format:


A is the nucleon number
Z is the proton number
X is the symbol of the element


Let’s consider the following example:

Isotopes of Hydrogen
Isotope name Components Structures
Protium 1 proton

1 electron

0 neutron

Deuterium 1 proton

1 electron

1 neutron

Tritium 1 proton

1 electron

2 neutrons

As you can see, the different atoms of hydrogen all have one proton and one electron but the numbers of neutrons are different.

Radioactive Isotopes

Some isotopes are radioactive; for example, in the above example, tritium is radioactive whereas the other 2 are not. The nuclei of radioactive isotopes are unstable and give off radiation. Take a look at an example below, focusing on radioactive isotopes of uranium:


***This is the end of this guide. Hope you enjoyed it! Thanks for using! We hope you will give us a chance to serve you again! Thank you!

Leave a comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.