Explain the change in first ionisation energy across period 2

Ionisation energy increases overall because nuclear charge increases with no significant increase in shielding, so it becomes more difficult to remove the outer electron.Ionisation energy decreases going from beryllium to boron as an electron is now being removed from a 2p orbital rather than a 2s orbital. 2p orbitals are higher in energy so it is easier to remove an electron.Ionisation energy decreases going from nitrogen to oxygen because now electrons are paired in orbitals so the electron removed from oxygen is repelled more by the other electron in its orbital so is easier to remove.