Unit 1: Section 1 – Particles and Radiation

Atomic Structure

Atoms are made up of protons, neutrons and electrons. The nucleus contains protons and neutrons known as nucleons. Orbiting the nucleus are the electrons.

Each atom is about 1x10-10m in diameter. Although the nucleus is only small, the majority of the diameter arises from the vast distances the electrons orbit at.

Proton number

The proton number is the number of protons in the nucleus. Usually the proton number is referred to by the letter Z and is found on bottom when written in standard notation.

It is the proton number that defines an element; no two elements have the same number of protons.

If an atom is described as being neutral, the number of electrons orbiting the nucleus equals that of the number of protons found in the nucleus. The number of electrons in an atom determines the way an element reacts and their chemical behaviour and therefore the proton number can tell you a large amount about an elements chemical property.

Nucleon Number

The nucleon number is also known as the mass number, and is represented by the symbol A. It describes the number of protons and neutrons found in the nucleus.

Isotopes

“Atoms with the same number of protons but different number of neutrons”

A difference in the number of neutrons affects the stability of the nucleus, usually the higher the number of neutrons in comparison to the number of protons, the greater the level of instability.

	Created by Leah Stevens about 11 years ago

A Level Physics Note on Unit 1: Section 1 - Particles and Radiation, created by Leah Stevens on 18/11/2013.