Ionisation energies

Question 1

how do we know that electrons exist in shells round a nucleus?

Answer 1

we can use spectroscope to analyse the electromagnetic radiation emitted by excited electrons when they return to their energy level

Question 2

we can find evidence for different energy levels using

Answer 2

electron emission spectra

Question 3

electron emission spectra works

Answer 3

by passing an electric current through atoms in a gaseous state, making the electrons move to higher energy levels. eventually the electrons return to their lower energy level, emitting electromagnetic radiation as they do so.we can analyse this electromagnetic radiation using a spectroscope

Question 4

when excited electrons return to their energy level, only

Answer 4

specific frequencies are emitted, unique to the individual element

Question 5

the fact that only specific frequencies of electromagnetic radiation rather than a continuous spectrum is emitted shows that

Answer 5

the energy of electrons can only have fixed values, meaning they are quantised (rather than continuous), which is evidence that electrons exist in shells

Question 6

ionisation energy is

Answer 6

a measure of the energy required to completely remove an lectron from one mole from an atom/charged particle of an element

Question 7

we can represent the first ionisation energy of an element, A, by the equation

Answer 7

A(g) = A+(g) + e-

Question 8

we can represent the second ionisation energy of A by the equation

Answer 8

A+(g) = A2+(g) + e-

Question 9

when we list successive ionisation energies of an element, we see

Answer 9

a steady increase with big jumps

Question 10

the big jumps in successive ionisation energies of an element are evidence of

Answer 10

the existence of quantum shells

Question 11

the first electron is considerably

Answer 11

easier to remove than the second

Question 12

there is a steady rise in

Answer 12

ionisation energy for the next eight electrons (to the ninth)

Question 13

when we reach the tenth electron in, for example sodium, there is a

Answer 13

big jump in ionisation energy

Question 14

explain the trend of the ionisation energies of sodium, Na. (the jumps are from the 1st to 2nd ionisation energies and the 9th to 10th ionisation energies. there are 11 electrons to be removed)

Answer 14

the first electron to be removed is in the third quantum shell of highest energy, so is furthest away from the nucleus and easiest to remove. the next eight electrons are in the second quantum shell of lower energy than the third, so there is a jump from the 1st to 2nd. these ionisation energies steadily increase due to the reduced electron-electron repulsion (shielding) and the positive to negative ratio increases. the jump from the 9th to 10th ionisation energies indicates that the 10th electron is in the first quantum shell of lowest energy and closest to the nucleus.

Question 15

shielding is

Answer 15

the electron-electron repulsion which occurs in an atom or ion, in the quantum shells

Question 16

the electron lost during ionisation is so far removed from the influence of the influence of the nucleus that it no longer

Answer 16

experiences an attractive force from the nucleus

Question 17

once an electron is removed from the influence of the nucleus, it is said to be

Answer 17

at an infinite distance from the nucleus

Question 18

to be removed, the energy of an electron has to be

Answer 18

increased to a particular value

Question 19

for a given atom, the energy value that the electron has when it reaches the ‘infinite distance’ from the nucleus is always

Answer 19

the same, regardless of where in the atom the electron has come from

Question 20

if an electron already has a high energy, then the energy it needs to gain in order to be removed will

Answer 20

not be very large

Question 21

ionisation energy is

Answer 21

the difference in energy between the electron when it has been removed and the energy it has when it is in its original orbital in the quantum shell

Question 22

Ionisation Energy (IE) =

Answer 22

IE = energy of electron when removed - energy of electron when in the orbital

Question 23

an electron in a low quantum shell, such as 1s, will need……….energy to be removed

Answer 23

much more energy than an electron in a higher quantum shell

Question 24

the first ionisation energy of an element is

Answer 24

the energy required to remove an electron from each atom in one mole of atoms in the gaseous state

Question 25

the second ionisation energy of an element is

Answer 25

the energy required to remove an electron from each singly charged positive ion in one mole of positive ions in the gaseous state

Question 26

both hydrogen and helium have their outer most electron in the 1s orbital, however, these electrons have different ionisation energies. explain why (bullet points of answer)

Answer 26

• 1s orbital of helium contains two electrons, so there is a shielding effect whereby these electrons have a greater energy, so the outer electron will have a lower ionisation energy
• helium also has a greater nuclear charge (two protons in the nucleus instead of one) so actually the attraction is greater in the 1s orbital, so the outer electron has less energy
• this means helium’s first ionisation energy is higher than that of hydrogen

Question 27

the factors that affect the energy of an electron has are: (3 items)

Answer 27

1) the orbital in which the electron exists
2) the nuclear charge of the atom (number of protons in the nucleus)
3) the repulsion (shielding|) experienced by the electron from all the other electrons present

Question 28

lithium’s first ionisation energy is lower than that of helium. explain why

Answer 28

lithium does have a greater nuclear charge, meaning the outer electron will have a lower energy, however, lithium’s outer electron i in the 2s orbital, meaning it experiences a greater shielding effect form the two inner 1s electrons. this means the outer electron has a higher energy form its position, which explains the why lithium’s first ionisation is lower than helium’s

Question 29

across a period, the trend is (ionisation energies)

Answer 29

an increase

Question 30

explain the trend for ionisation energies across a period (excluding d block elements)

Answer 30

ionisation energy increases across a period as the increased nuclear charge across a period has a greater effect on the outer electron than shielding, decreasing its energy, and so increasing ionisation energy

Question 31

down a group, the tend for ionisation energies is

Answer 31

a decrease in the value

Question 32

the three factors which explain the trend for ionisation energies down a group are:

Answer 32

the nuclear charge increases each period, so increasing ionisation energy by decreasing the energy of the outer most electron. HOWEVER, each next member of a group has an extra quantum shell, which results in increased repulsion for the outer most electron. also, each new quantum shell has a higher energy than the previous one, so these two factors are more significant than the increased nuclear charge.

Question 33

the anomalies in the group ionisation energy trend are:

Answer 33

group 3 and 4

Question 34

the anomaly in group 4 is

Answer 34

lead which has a higher first ionisation energy than the element above it ( tin )

Question 35

in group 3, there is no

Answer 35

general trend in the first ionisation energies (boron to thallium)