Evidence for Electron arrangement (Ionisation Energy)

What is first ionisation energy?

The energy required to remove one electron from each atom in one mole of gaseous atoms, forming one mole of gaseous 1⁺ ions

Write the equation for first ionisation energy.

X(g) → X⁺(g) + e⁻

What 3 factors affect ionisation energy?

• Nuclear charge

• Distance from nucleus

• Shielding

How does nuclear charge affect ionisation energy?

More protons → stronger attraction → higher ionisation energy

How does distance affect ionisation energy?

Greater distance → weaker attraction → lower ionisation energy

What is shielding?

Inner electrons repel outer electrons, reducing nuclear attraction

How does shielding affect ionisation energy?

More shielding → weaker attraction → lower ionisation energy

What happens to ionisation energy down a group?

Decreases

Why does ionisation energy decrease down a group?

• Increased distance

• Increased shielding
  (outweighs nuclear charge)

What happens to ionisation energy across a period?

Increases

Why does ionisation energy increase across a period?

• More protons

• Same shielding
  → stronger attraction

Why is there a dip from Group 2 → Group 3? (e.g. Mg → Al)

• Electron removed from higher energy p orbital

• Easier to remove

Why is there a dip from Group 5 → Group 6? (e.g. P → S)

• Electron pairing in p orbital

• Electron repulsion makes removal easier

Why do ionisation energies increase successively?

• Less electrons → less repulsion

• Stronger attraction to nucleus

Why is there a big jump in ionisation energy?

Electron removed from a new inner shell