Specification Link

• Apply rules about the filling of electron shells (energy levels) to predict the electronic configurations of the first 20 elements in the periodic table as diagrams and in the form 2.8.1

• Describe the connection between the number of outer electrons and the position of an element in the periodic table

Electron Configuration

Apply the rules of electron shells to predict the configuration of the first 20 elements (D/C)

Describe the connection between the number of outer electrons and the position of an element in the periodic table (B/A)

Explain the significance of electrons shells in the way that substances react.

How are electrons arranged?Electrons are not evenly spread but exist in layers called shells. (The shells can also be called energy levels).

The arrangement of electrons in these shells is often called the electron configuration.

Note that this diagram is not drawn to scale – the atom is mostly empty space. If the electrons are the size shown, the nucleus would be too small to see.

1st shell

2nd shell

3rd shell

How many electrons per shell?Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first.

1st shell holdsa maximum of2 electrons

2nd shell holdsa maximum of8 electrons

3rd shell holdsa maximum of8 electrons

This electron arrangement is written as 2,8,8.

Electrons in an atom are arranged in electron shells, or energy levels around

the nucleus.

• Electrons are showing using dots or crosses• Circles represent the shells.• 1st (inner shell) holds 2 electrons.• 2nd shells holds 8 electrons.• 3rd shell holds 8 electrons.

Anyone can understand about atoms

Apply the rules of electron shells to predict the configuration of the first 20 elements (D/C)

Peer assess each others before the answers are

revealed!

The electronic configuration of an element is 2.8.7. What information does this give

about the element and its atoms?

The electronic configuration 2.8.7 shows that the atom contains two electrons in its first shell,

eight electrons in its second and seven electrons in its third, outer shell. The atom is

in group 7, period 3, of the periodic table.Describe the connection between the number of outer electrons and the position of an element in the periodic

table (B/A)

The groups and periods of the periodic table

• The group numbers are the same as the number of electrons in the outer shells.

• (Apart from group 0, where the other shells are full.

• The number of electron shells is the same as the period number.

The electronic configuration of lithium is 2.1.The electronic configuration of sodium is 2.8.1.(1) Explain, in terms of their electronic

configurations, why lithium and sodium are both in group 1 of the periodic table.

(2 marks)

(2) Explain, in terms of their electronic configurations, why lithium is placed in period 2 and sodium is placed in period 3 of the periodic table.

(2 marks)

Answer Acceptable answers Mark

An explanation linking · (both have) one electron (1)· in the outer shell/orbit/energy level (1)do not award first mark if proton/neutron/atom (in outer shell)

both have one outer electron (2) both need to lose 1 electron to have a full outer shell (2) fully correct diagrams of lithium and sodium showing electronic configurations (1) have the same number of electrons in the outer shell (1)

(2)

An explanation linking · lithium has 2 shells/orbits/energy levels (1)· sodium has 3 shells/orbits/energy levels (1) max 1 mark if outer/full shells max 1 mark if rings/circles/layers

If no marks awarded from 'answer' column, allow any one from sodium is more reactive than lithium ORA (1) sodium has more electrons than lithium ORA (1) sodium has more shells than lithium ORA (1) ignore reactivity increases down the group

(2)