8.4 ionisation énergies

Question 1

Period 3:
Na, Mg, Al, Si, P, S, Cl, Ar

Why does first ionisation energy drop between Mg and Al, when its supposed to be increasing across a period

Answer 1

Mg: 1s2 2s2 2p6 3s2
Al: 1s2 2s2 2p6 3s2 3p1

Mg loses a 3s electron whilst Al loses a 3p electron.
The p electron is already at a higher energy level than the s electron so it takes less energy to remove

Question 2

Period 3:
Na, Mg, Al, Si, P, S, Cl, Ar

Why does first ionisation energy drop between P and S

Answer 2

Electrons in a pair will be easier to remove than one In its own orbital because its already being repelled by the other electron

P shell has 3 orbitals, so 3 pairs.

P: 1s2 2s2 2p6 3s2 3p3 Has no paired electrons in a p orbital because each p electron is in its own orbital.

S: 1s2 2s2 2p6 3s2 3p4 Has two of its p electrons paired in a p orbital so one of these is easier to remove than an unpaired one due to repulsion of electrons in the same orbital

Question 3

What are successive ionisation energies

Answer 3

If you remove electrons from atoms one at a time, each one is harder to remove than the one before.

E(g) —> E+(g) +e-(g)
E+(g) —-> E2+(g) + +e-(g)
E2+(g) —-> E2+(g) + e-(g)

Question 4

How do you describe ionisation energies from a graph

Answer 4

. Closer to y axis, the further out the shells

.Number of points before a big spike is the number of electrons on outer energy shell, so determines the group the element is in

. There is a sharp increase in energy when moving down a shell because electrons are getting closer to nucleus

.Energy between electrons on the same shell increase slightly