1.4 Ionisation energy

State what causes ionisation energy.

Ionisation energy is caused by the attraction between the nucleus and the outer electron.

Define the term ionisation energy.

Ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions.

Define the first ionisation energy.

The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1⁺ ions.

Define the second ionisation energy.

The second ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous 1⁺ ions to form one mole of gaseous 2⁺ ions.

Write the equation for the first ionisation energy of calcium.

Ca(g) → Ca⁺(g) + e⁻.

Write the equation for the second ionisation energy of calcium.

Ca⁺(g) → Ca²⁺(g) + e⁻.

Describe the trend in ionisation energy across a period.

Ionisation energy increases across a period because nuclear charge increases, atomic radius decreases, shielding remains constant, and the outer electrons are held more tightly.

Describe the trend in ionisation energy down a group.

Ionisation energy decreases down a group because the atomic radius increases, shielding increases, and the outer electrons are further from the nucleus and held less tightly.

Explain why ionisation energy increases across a period.

Nuclear charge increases, pulling electrons closer; the atomic radius decreases and shielding stays constant, so more energy is needed to remove electrons.

Explain why ionisation energy decreases down a group.

The number of electron shells increases, increasing distance and shielding, which weakens nuclear attraction on outer electrons.

State the factors that affect ionisation energy.

Nuclear charge, atomic radius, electron shielding, and the distance of outer electrons from the nucleus.

Explain why successive ionisation energies increase for an element.

After each electron is removed, the attraction between the nucleus and remaining electrons increases due to decreased shielding and increased proton-to-electron ratio.

Explain how successive ionisation energy data can determine an element’s group.

A large jump in ionisation energy indicates removal of an inner shell electron; the number of electrons before the jump equals the number of outer shell electrons, which corresponds to the group number.

Deduce what a large jump in successive ionisation energy means.

It shows that an electron is being removed from a new, inner shell closer to the nucleus, where nuclear attraction is stronger.

Describe how shielding affects ionisation energy.

Increased shielding from inner shells reduces nuclear attraction on outer electrons, lowering ionisation energy.

Explain the relationship between proton-to-electron ratio and ionisation energy.

A higher proton-to-electron ratio increases attraction on remaining electrons, making them harder to remove and increasing ionisation energy.

State why ionisation energy is always positive.

Energy must be supplied to overcome the attraction between the nucleus and the electro