2. ionisation energies

Question 1

definition

the first ionisation energy

Answer 1

the first ionisation energy is the energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms

Question 2

what is ionisation?

Answer 2

the removal of 1 or more electrons

Question 3

is ionisation exothermic or endothermic?

why?

Answer 3

endothermic

have to put energy in

Question 4

the lower the ionisation energy

Answer 4

the easier it is to form an ion

Question 5

e.g. equation for first ionisation energy of oxygen

Answer 5

O(g) -> O+(g) + e-

Question 6

how does nuclear charge affect ionisation energy

Answer 6

more protons =
more positive charge =
stronger attraction to electrons =
more energy needed

Question 7

how does atomic radius affect ionisation energy

Answer 7

attraction decreases rapidly with distance
electron closer to nucleus (smaller atomic radius) more strongly attracted
than electron further away from nucleus (large atomic radius)

Question 8

how does shielding affect ionisation energy

Answer 8

number of electrons between outer electrons and nucleus increases
outer electrons less attracted to nuclear charge

Question 9

a high ionisation energy means

Answer 9

strong attraction between electron and nucleus
so more energy is needed to overcome attraction
to remove electron

Question 10

does ionisation energy increase or decrease as you go down a group

Answer 10

decrease

Question 11

why does ionisation energy decrease down a group

4 points

Answer 11

1. down the group elements have extra electron shells
2. atomic radius larger. outer electrons further away from nucleus. attraction reduced.
3. extra inner shells shield outer electrons from attraction to nucleus
4. although increased nuclear charge this effect is overridden by effect of extra shells.

Question 12

does ionisation energy increase or decrease as you go across a period

Answer 12

increase

Question 13

why does ionisation energy generally increase as you go across a period?

Answer 13

1. number of protons increasing
2. • charge increases. electrons pulled closer to nucleus. atomic radius smaller.
3. extra electrons added to outer energy level/shell. don’t provide any extra shielding affect

Question 14

what are the 2 exceptions to the trend that ionisation energy increases across period

Answer 14

1. first ionisation energy decrease between groups 2 & 3
2. first ionisation energy decrease between groups 5 & 6

Question 15

why does ionisation energy drop between group 2 and 3

Answer 15

1. sub shell structure
2. outer electron in group 3 elements is a p orbital rather than s orbital
3. p orbital slightly higher energy than an s orbital
4. electron is found further from the nucleus
5. p orbital also has more shielding provided by s electrons
6. overrides effect of increased nuclear charge.

Question 16

why does ionisation energy drop between group 5 and 6

Answer 16

1. p orbital repulsion.
2. group 5 electron is removed from singly occupied orbital.
3. group 6 electron removed from orbital containing 2 electrons
4. repulsion between 2 electrons in an orbital = electrons easier to remove from shared orbitals.

Question 17

e.g. of equation for 2nd ionisation energy of oxygen

Answer 17

O+(g) -> O2+(g) + e-

Question 18

within each shell successive ionisation energies increase or decrease?

Answer 18

increase

Question 19

within each shell why do successive ionisation energies increase

Answer 19

electrons are being removed from increasingly positive ion
less repulsion amongst remaining electrons
electrons held more strongly by nucleus

Question 20

when do the big jumps in the ionisation energy of an element happen and why

Answer 20

when a new shell is broken into

electron is being removed from a shell closer to the nucleus