Starter Physics

Atoms

Everything is made of atoms.

Every object, every material, even the air we breath, is made of atoms.
Atoms are very tiny particles - thousands of times smaller than we can see with the most powerful optical microscopes.
Atoms come in different types, which define the properties of the material.
The different types are known as the 'chemical elements', for example Iron is different from Oxygen or Gold.

Atoms are made from even smaller particles, known as protons, neutrons and electrons.
Protons and neutrons live in the centre in the nucleus, with the electrons whizzing around it, as if in orbit. The electrons move so fast that we say that it is an 'electron cloud'.
The simplest atom is Hydrogen which has 1 particle (a proton) in its nucleus, and 1 electron orbiting.
The next is Helium which has 2 protons and 2 neutrons in the nucleus, with 2 electrons orbiting.
Each chemical element has a different number of protons, neutrons and electrons, with heavier materials having more protons, neutrons and electrons.
Chemical elements can react with each other to form all of the materials we see around us.

The atomic structure of Hydrogen and Helium.

Image credit: BruceBlaus, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons

Electrons and protons have an electric charge.
Electrons are negatively charged, protons are positively charged, by the same amount.
In some materials, such as metals, the electrons are not tightly bound to the atoms, they can be free to move.
The movement of electrons is what enables electric circuits to work.
This is why metals are used in electric circuits and in electrical wires.
We would need over 6 billion billion electrons (or protons) to make 1 Coulomb of charge.

The first 20 elements are listed below:

The atomic number is the same as the number of protons.
Because protons and neutrons have almost identical mass, the atomic mass number is the number of protons plus neutrons.

Chemical elements can react with each other to form the 'molecules' that make up all of the materials we see around us.
They like to bond with other elements because when bonded they are in stable lower energy states.
They can react spontaneously if the energy difference is favourable.
The change in energy when a molecule is formed is often released in the form of heat.
To break up the molecule we would need to put energy in.

A molecule of water (H₂O) is made from 1 oxygen and 2 hydrogen atoms.

Image credit: MsKDinh, CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0), via Wikimedia Commons