Module 3- Patterns In The Periodic Table Flashcards
How and why does AR change going across the periodic table?
Decreases from left to right, each successive element gains another electron and proton, pulling the outer electrons closer to the nucleus
How and why does AR change down a group?
Each successive element down a group has another shell of electrons and increased shielding, reducing the attraction to outer electrons and so they are pulled less towards the nucleus
Definition of 1st ionisation energy?
Energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a +1 charge
How and why does 1st ionization energy change across the period??
More protons in the nucleus, pulling the outer electrons with more attraction, and so AR is decreased. This makes it harder to remove the outer electron because of the increased nuclear attraction
How and why does 1st ionisation energy change down a group??
AR increases because of more electron shells, therefore ionisation energy decreases. More shells between the outer electron and nucleus and bigger AR outweighs the increase in protons, so less energy is required to remove the outer electrons
Generally equations for 1st, 2nd, 3rd ionisation energy
M (g)-> M+ + e-
M+ (g)-> M2+ +e-
M2+ (g)->M3+ +e-
Why does B have a lower I.E than Be despite being the successive element of Be??
Because it’s outer electron is removed from the 2p sub shell rather than the 2s sub shell, which is at a slightly higher energy level and further away from the nucleus, as well as slightly more shielded from the 2s sub shell. Therefore it needs slightly less energy to remove than Be’s outer electron
Why does oxygen have a slightly lower IE than nitrogen when the electrons are coming from the same 2p subshell??
Although the first electron is coming from the 2p subshell for both elements, the oxygen electron is coming from the p orbital that already has an electron in, whereas nitrogen’s electron has a p orbital of its own. There is repulsion between the two electrons sharing the P orbital, making it slightly easier to remove one of them
Why is there a big jump in ionisation energy Between the 7th and 8th electron in fluorine, which has 9 electrons??
The first 7 electrons are being removed from the 2nd shell, out of the subshells 2s and 2p. After the 7th electron, the ionisation energy increases because the electrons left are in the 1s subshell, at a lower energy level that requires much more energy to remove
