ELECTRON CONFIGURATION

Electrons

It is the electrons that control chemistry. How an atom interacts with others to form compounds and undergo chemical reactions all depends on the number of electrons and how they are arranged.

Electron configuration

Is the way the electrons are arranged around the nucleus

We use Bohr’s model of the atom to show where the electrons are in the first 18 elements – the diagram you end up with is known as a Bohr diagram

Bohr diagram for carbon

C

The rules are:

1. The number of electrons equals the number of protons

2. The first electron shell can hold 2 electrons

3. The second and third shells can hold 8 electrons each

(beyond the third things get more complicated and you don’t need to know right now)

Let’s look at carbon The atomic number

of carbon is 6 the number of

protons is 6 the number of

electrons is 6

If carbon has 6 electrons and the first shell can hold 2, how many electrons are in the second shell?

We can write this as2.4

CC

Here is another example The element has 11 protons

2 electrons in the first shell 11-2 = 9

Only 8 will fit in the second shell So, there is 1 in the third shell

Write this as 2.8.1

Your turnCopy and complete this table