Atomic Structure

Relative Atomic Mass

The mean mass of an atom compared with 1/12^th of the mass of a carbon 12

1st Ionisation Energy

Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

3 factors which affect ionisation energy

1. Number of electron shells - distance of the electron from the nucleus

2. Shielding

3. Size of nuclear charge

How does the following factor affect ionisation energy : Number of electron shells

The further an electron is from the nucleus, the lower the force of attraction. This means that the electron will be easier to remove which means the ionisation energy will be lower.

How does the following factor affect ionisation energy : Shielding

Inner‑shell electrons repel outer‑shell electrons, reducing the effective nuclear charge felt by the outer electron. With weaker attraction, less energy is needed to remove the outer electron, so ionisation energy decreases.

How does the following factor affect ionisation energy : Size of nuclear charge

The more protons in the nucleus, the higher the nuclear charge, the harder it is to remove an electron because the nucleus attracts electrons more strongly so the higher the ionisation energy.

What does a large jump in ionisation energies indicate?

Movement to another electron shell closer to the nucleus

Ionisation energies are greater the closer to the nucleus.

True / False

True - The electrostatic attraction is stronger.

Pattern in ionisation energies down a group

• More shells

• More shielding

• Increase in nuclear charge (outweighed by more shielding)

• Less attraction so less energy required to remove an electron so lower IE

Patterns in ionisation energies across a period

• Same shells

• Similar shielding

• Increase in nuclear charge

• Greater attraction so more energy required to remove electron so higher IE