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Chem unit 1 as aqa

can someone please urgently explain ionisation energies to me because i just don't get it, like trends across period 1 2 and 3 etc
Reply 1
Ionisation energy is the energy required to remove one mole of electrons from one mole of a vaporised element, to form one mole of unipositively charged ions.

The ionisation energy increases across the period, because the proton number increases. The effective nuclear charge is subsequently larger, so the force of electrostatic attraction between the highest energy electron and the atomic nucleus is greater, so it requires increasingly large amounts of energy to remove this electron across the group.

The ionisation energy decreases down the group, because shielding electron shells exert a dampening effect on the magnitude of electrostatic attraction between the highest energy electrons and the atomic nucleus. So it requires less energy to permanently displace these electrons, and the ionisation energy is subsequently lower.
Reply 2
I have a question about electron configuration. When should you use 1s(2) 2s(2) 2p(6) 3s(2) 3p(6) 3d(10) 4s(2) 4p(6)...
And when should you use
1s(2) 2s(2) 2p(6) 3s(2) 3p(6) 4s(2) 3d(10) 4p(6)
Original post by Dyl98an
I have a question about electron configuration. When should you use 1s(2) 2s(2) 2p(6) 3s(2) 3p(6) 3d(10) 4s(2) 4p(6)...
And when should you use
1s(2) 2s(2) 2p(6) 3s(2) 3p(6) 4s(2) 3d(10) 4p(6)


It is the same thing, you wouldn't lose marks for writing the 4s orbital first, in fact you should do it if the electronic configuration ends in 4s2 however if the config goes further than 4s2 it will be better for you to write it in numerical order.
Original post by TARS
Ionisation energy is the energy required to remove one mole of electrons from one mole of a vaporised element, to form one mole of unipositively charged ions.

The ionisation energy increases across the period, because the proton number increases. The effective nuclear charge is subsequently larger, so the force of electrostatic attraction between the highest energy electron and the atomic nucleus is greater, so it requires increasingly large amounts of energy to remove this electron across the group.

The ionisation energy decreases down the group, because shielding electron shells exert a dampening effect on the magnitude of electrostatic attraction between the highest energy electrons and the atomic nucleus. So it requires less energy to permanently displace these electrons, and the ionisation energy is subsequently lower.


I don't understand why lithium has the highest ionisation one minute then the next its a different element. also confused with carbon having second and third ionisation energy wtf

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