Electronic structure

What you need to know

• Electrons occupy the lowest available energy levels first.
• The lowest available energy levels are the innermost available shells.
• Electronic structure can be represented using numbers or a diagram.
• You should be able to represent the first twenty elements in both forms.

The big picture

Electrons in an atom occupy the lowest available energy levels, starting with the innermost available shells. Electronic structure can be shown as numbers or as a diagram. For example, sodium is written as 2,8,1: two electrons in the lowest energy level, eight in the second and one in the third. You need to be able to represent the electronic structures of the first twenty elements in both forms.

How electronic structure is built

Follow the arrangement from the lowest available energy level outwards.

1. 1

   Start at the lowest level

   Electrons occupy the lowest available energy levels first, so begin with the innermost available shell.

2. 2

   Move outwards when needed

   Electrons occupy higher energy levels only after the lower available levels have been used.

3. 3

   Record the arrangement

   The finished electronic structure can be represented as numbers or shown as a diagram.

Unpacking sodium: 2,8,1

Each number tells you how many electrons are in one energy level.

Electronic structure vocabulary

Keep the language tied to what the representation is showing.

Predict, then check

Use the order of the numbers rather than guessing from their size.

In the electronic structure 2,8,1, which statement correctly describes the electrons?

Memory hook

Inside first: electrons take the lowest available energy levels before moving outwards.

Check yourself

What does each number in sodium’s electronic structure 2,8,1 tell you?