Atomic Structure

What is an Atom?

An atom is the smallest piece of an element that can exist.
is made of atoms.
Atoms are very small. 7 million atoms joined together
in a straight line would be about 1mm long.

What is the Structure of an Atom?

All atoms have a nucleus (the big bit in the middle).
The nucleus contains protons and neutrons.

All atoms have electrons.
The electrons are in shells around the nucleus.
For any atom, the number of protons is
the same as the number of electrons.
If an atom loses or gains electrons it is called an ion.

Below is a picture of a sodium atom.
It has 11 protons, 11 electrons and 12 neutrons.

The Atom showing Electrons, Neutrons and Protons.Proton Neutron Electron

The electron structure is 2, 8, 1.

Each proton has an electrical charge of +1.
Each electron has an electrical charge of -1.
The neutron has no charge (it is neutral).

An atom has the same number of protons and electrons
so the overall charge is zero (it is neutral).

The mass of a neutron and a proton are the same.
An electron is very much smaller,
about 1 ÷ 2000 times the size of a proton
although it has an equal and opposite electrical charge.

The electrons, although tiny, take up most of the space of an atom.
This means that most of the space that an atom fills
contains hardly any mass. An atom is mostly empty space
with nearly all the mass centred at the nucleus.


Particle Relative Mass Relative Charge
Proton 1 +1
Neutron 1 0
Electron 0·0005 -1

The protons, neutrons and electrons are shown as coloured to
distinguish them from each other. In reality they have no colour.

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