#### Atoms?

Everything in the universe is made of atoms. Atoms join (bond) together in different ways to create everything around you. The study of how atoms behave is called Chemistry. So this page is pretty essential - you've got to memorise most of this page. Let's get started!

• Add labels to an atom
• Describe an atom's structure
• Give the charge and mass of each sub-atomic particle
• State how charges will interact with each other

#### Describing an Atom

Atoms are made of three different sub-atomic particles. They are called protons, neutrons and electrons. The protons and neutrons occupy the centre of the atom and form a dense ball called the nucleus. The electrons move around the outside of the atom in regions called electron shells. This is shown in the diagram above. Note that the diagram has five labels, i) protons, ii) neutrons, iii) electrons, iv) nucleus and v) electron shells. Exam Tip . Notice that the number of electrons is the same as the number of protons (but only in an atom).

#### Charges and Masses

Over time we've discovered that protons, neutrons and electrons have lots of different properties. The two you need to worry about are called charge and mass. Protons have a positive charge and a mass of one. Electrons have a negative charge and a mass of nearly zero (small fib). Neutrons have a neutral charge (often called zero/no charge) and a mass of one. Note that mass has no units here - you'll find out why later. This information is shown in table form below. Exam Tip

The number of electrons and protons is the same - their charges cancel each other - so atoms have a charge of zero overall.

Sub-atomic Particle Charge Mass
Proton +1 1
Neutron Neutral 1
Electron -1 0

#### Electrostatic Interactions

This is a scary phrase for something simple. Opposite charges attract and like charges repel. So if two protons are placed next to each other, they both have a positive charge, they repel each other and move apart. If you place an electron next to a proton, they have the opposite charge and will therefore attract each other. This might remind you of how magnets behave - it's the same force at play.