Chemistry - Periodic Table and Energy - Perodicity

What is the definition of the first ionisation energy?

The amount of energy required to remove one mole of electrons from one mole of a gaseous atom.

Why does beryllium have a higher first ionisation energy than boron, despite boron having more protons?

Beryllium has a stable S sub shell and boron has an unstable P sub shell, meaning it takes less energy for the electron to be removed.

Why does oxygen have lower ionisation energy than nitrogen, despite having more electrons in its P sub shell?

The extra electron in the 2px subshell spins the opposite way and therefore repels its electron pair, whereas nitrogen only has attracting electrons.

What are the trends in first ionisation energies going down periods 2 and 3?

• As you go down the period, IE increases. The noble gases have the highest IE on the periodic table. This is because there is more protons attracting the negative electrons.

• As atomic radius increases, the IE decreases as the valence shell gets further away from the nucleus.

What does a sharp increase in IE indicate?

That we have moved on to a new shell.