Loading please wait

The smart way to improve grades

Comprehensive & curriculum aligned

Try an activity or get started for free

Understand Electron Structure

Worksheet Overview

Niels Bohr worked out that electrons can only be in certain parts of the atom. In this activity, you will learn how to apply his rules, and start to understand how useful they are.

 

Bohr worked out that electrons move around in shells, around the nucleus. For example, a potassium atom is drawn like this:

 

The structure of a potassium atom

 

Potassium has the atomic number 19 and mass number 39, so there are 19 protons and 20 neutrons in the nucleus. Because there are 19 protons, there must be 19 electrons to make a neutral atom. They are spread across four shells, according to these rules:

 

The first shell, closest to the nucleus, can only take 2 electrons.

The second shell can only take the next 8 electrons.

The third shell takes the next 8 electrons.

The fourth shell takes the remaining electrons.

 

These rules start to work differently if there are more than 20 electrons, but you won't be asked about that situation in a GCSE exam.

So, for potassium, we think about the electrons this way:

 

Potassium has the atomic number 19, so there are 19 electrons to put in place. The first two fill up the first shell, so there are 17 left. The next 8 fill up the second shell, so there are 9 left. The next 8 go into the third shell, so there's only one left, which must go into the fourth shell.

 

Sometimes people draw the atom out with the nucleus and shells. You will also sometimes see the electron structure written as numbers, separated by dots or commas. The numbers start with the first shell, then come in order, so potassium is 2.8.8.1 or 2,8,8,1.

 

It took a while for scientists to work out these rules, but they became very useful. It turned out that a lot of patterns in how different elements behave and react depend on how many electrons there are in the outermost shell. For example, lithium, sodium and potassium all have 1 electron in their outermost shells. The next few activities will help you to understand this even better.

 

Let's move on to some questions now.

What is EdPlace?

We're your National Curriculum aligned online education content provider helping each child succeed in English, maths and science from year 1 to GCSE. With an EdPlace account you’ll be able to track and measure progress, helping each child achieve their best. We build confidence and attainment by personalising each child’s learning at a level that suits them.

Get started
laptop

Try an activity or get started for free

  • National Tutoring Awards 2023 Shortlisted / Parents
    National Tutoring Awards 2023 Shortlisted
  • Private-Tutoring-WINNER-EducationInvestor-Awards / Parents
    Winner - Private Tutoring
  • Bett Awards Finalist / Parents
    Finalist
  • Winner - Best for Home Learning / Parents
    Winner - Best for Home Learning / Parents