A Visual Encyclopedia of the Periodic Table

12

Inside an atom

An atom is the smallest unit of an element. Atoms are too small to see

(even with the most powerful microscopes) but they are everywhere.

They consist of smaller particles called protons, neutrons, and

electrons. Every element has a unique number of protons.

Lithium atom

Uranium atom

U

92

Hydrogen atom

H

1

What’s the atomic number?

The number of protons in an atom of an element is

called the atomic number. The atomic number of an

atom identifies the element it belongs to. Every atom

also has an equal number of electrons. For elements

found naturally on Earth, hydrogen has the smallest

atomic number (1), while uranium atoms have the

highest atomic number (92).

Electron ❯ The tiny,

negatively charged

particles in an atom are

called electrons. They

are involved in the way

the atoms of an element

react and form bonds

with the atoms of

other elements.

Shell (^) ❯ The electrons in an atom move
around the nucleus. They are arranged
in layers called shells. When reacting
with each other, atoms tend to fill up
their outer shells to become more stable.
Seven shells house
the 92 electrons in
a uranium atom.
Atomic
number
This shell is the space
in the hydrogen atom
where one electron
circles the proton at
the centre of the atom.
In a lithium atom,
two shells house
three electrons, which
circle the protons and
neutrons at the centre.
Li
3
Introduction
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