I/GCSE Chemistry: Ionisation energy

In I/GCSE Chemistry, we will learn about ionisation energy.

• In I/GCSE Chemistry,  it measured in kilojoules per mole (kJ mol^-1)
• 1^st Ionisation energy: Energy required to remove one mole of electrons from one mole of gaseous atoms, forming one mole of uni-positive ions in the gaseous state.

X (g) → X⁺ (g) + e⁻

• 2^nd Ionisation energy: Energy required to remove one mole of electrons from one mole of unipositive ions in the gaseous state.

X⁺ (g) → X²⁺ (g) + e⁻

• 3^rd Ionisation energy: Energy required to remove one mole of electrons from one mole of X²⁺ ions in the gas phase.

X²⁺ (g) → X³⁺ (g) + e⁻

• Electron shielding: The repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer-shell electrons.

• ATOMIC RADIUS: The greater the atomic radius, the greater the nuclear attraction experienced by inner electrons
• NUCLEAR CHARGE: The greater the nuclear charge, the greater the attractive force on outer electrons
• ELECTRON SHIELDING: Inner shells of electrons repel outer shell electrons. This is called electron shielding
  • The more inner shells there are, the larger the shielding effect, the smaller the nuclear attraction experienced by the outer electrons

• As you go down a group, the electron being removed occupies a higher energy and is FURTHER AWAY from the nucleus.
• The force of attraction between the negatively charged electron being removed and the positively charged nucleus DECREASES.

• In I/GCSE Chemistry,  elements INCREASES as you go across a period because the electron being removed is more strongly bound to the nucleus (greater attraction) and has an increasing nuclear charge
• As the atomic radius decreases, the negatively charged electron being removed is CLOSER to the positively charged nucleus- DIFFICULT to remove electron

In I/GCSE Chemistry,

• 2^nd ionisation energy is GREATER than 1^st ionisation energy because as each electron is moved, there is LESS repulsion between electrons, and each shell will be drawn CLOSER to nucleus - LESS shielding from inner electons
• Also because the distance of each electrons from the nucleus DECREASES- the nuclear attraction INCREASES, and MORE ionisation energy is needed to remove the successive electron
• 3^rd ionisation energy is GREATER than the 2^nd ionisation energy because you are trying to remove a negatively charged electron from an ion with a 2+ charge

You got it now!

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