ionisation energy trends

Question 1

factors affecting ionisation energy

Answer 1

nuclear charge, atomic/ionic size and shielding effect by inner shell electrons

Question 2

how does nuclear charge affect ionisation energy?

Answer 2

as nuclear charge increases, there is stronger attraction for valance electrons and more energy is required to remove an electron hence ionisation energy increases

Question 3

how does atomic radii and ionisation energy change down a group?

Answer 3

down a group, atomic radii increases because there are more shells of electrons present and ionisation energy decreases

Question 4

how does atomic radii and ionisation energy change across a period?

Answer 4

across a period, nuclear charge increases and electrons are more strongly attracted by the nucleus hence each individual shell becomes smaller and atomic radii decreases, causing ionisation energy to increase

Question 5

how does ionic radii (for 2nd ie) change across a period?

Answer 5

decreases across a period, anion (-) > neutral atom > cation (+)

Question 6

why is a neutral atom bigger than its cation?

Answer 6

cations are smaller due to stronger attractions between remaining electrons and the nucleus, and one shell of electrons being lost in the formation of cation

Question 7

why is a neutral atom smaller than its anion?

Answer 7

anion is bigger due to the extra repulsion produced by the additional/incoming electrons which causes the shell to expand

Question 8

ionisation energy trend for isoelectronic species?

Answer 8

as ionic radii decreases, ionisation energy increases. as nuclear charge increases, the outermost electrons are more strongly attracted to the nucleus and ionic radii decreases

Question 9

trend of ionisation energy down a group?

Answer 9

down a group, atomic radii increases due to increasing number of shells of electrons and the valance electron is further away from the nucleus. no. of inner shells increase and valance electron is better shielded by inner shell electrons. increase in shielding effect outweighs the increase in effective nuclear charge, valance electron is less strongly attracted by nucleus, hence less energy is required to remove an electron and ie decreases

Question 10

trend of ionisation energy across a period?

Answer 10

across a period, nuclear charge increases and valance electron is nearer to the nucleus, causing atomic radii to fall while the shielding effect remains relatively constant. valance electrons become more strongly attracted by the nucleus and more energy is needed to remove an electron, hence ie increase

Question 11

exceptions: ns2 vs ns2np1 (Mg vs Al)

Answer 11

less energy is required to remove a 3p electron in Al than a 3s electron in Mg because the 3p subshell has a higher energy than the 3s subshell and first ie of Al will be lower than that of Mg

Question 12

exceptions: ns2np3 vs ns2np4 (P vs S)

Answer 12

in S, the 2 electrons occupying the same 3p subshell give rise to inter-electron repulsion and less energy is required to remove a paired 3p electron in S than an unpaired 3p electron in P, hence first ie of S is lower than that of P