Atoms are the basic building blocks of all matter. In this article, you will learn:
- What atoms are made of
- The differences between protons, neutrons and electrons
- How to find the number of each subatomic particle
What is an Atom?
An atom is the smallest particle of an element that still has the chemical properties of that element.
Every atom has two main parts:
- A tiny but very dense centre called the nucleus
- Electrons moving around the nucleus in electron shells
The protons and neutrons are found in the nucleus, while the electrons move around the nucleus in electron shells.
Subatomic Particles
Here are three subatomic particles in an atom:
| Subatomic Particle | Relative Mass | Relative Charge | Location |
|---|---|---|---|
| Proton | 1 | +1 | Nucleus |
| Neutron | 1 | 0 | Nucleus |
| Electron | 1/1840 | –1 | Electron shells |
Key Points:
- Protons and neutrons have almost the same mass.
- Electrons are much lighter and their mass is considered negligible.
- In a neutral atom, the number of protons equals the number of electrons so that the overall charge is zero.
Proton Number and Nucleon Number
Proton Number (Atomic Number)
- The proton number is the number of protons in an atom.
- It is also called the atomic number.
- You can find the proton number of any element at the top of its box in the Periodic Table.
- Every element has a unique proton number. This number determines the identity of the element.
Examples:
- Hydrogen → proton number = 1
- Carbon → proton number = 6
- Sodium → proton number = 11
Nucleon Number (Mass Number)
- The nucleon number (also called mass number) is the total number of protons and neutrons in the nucleus.
- The mass of an atom depends mainly on the protons and neutrons (electrons have negligible mass).
Formula: Nucleon number = Number of protons + Number of neutrons
You can find the nucleon number at the bottom of each element’s box in the Periodic Table.
Examples:
- Lithium → nucleon number = 7
- Nitrogen → nucleon number = 14
- Sulfur → nucleon number = 32
Summary
- Atoms consist of protons and neutrons in the nucleus, and electrons in electron shells.
- In a neutral atom: Number of protons = Number of electrons
- Nucleon number = Number of protons + Number of neutrons
Practice Questions
Test your understanding with practice questions on this topic. Try the questions first before checking the solutions.
