ionisation energy

Question 1

what is meant by the ionisation energy ?

Answer 1

the energy required to remove 1 mole of electrons from a mole of gaseous atoms

Question 2

so what happens when we ionise an element ?

Answer 2

we give the outer electron enough energy to leap from its ground state, past all energy levels so that it is separated from the element completely.

Question 3

what does the amount ionisation energy depend on ?

Answer 3

it depends on which energy sub level is the outer electrons founded in so electrons in the d block will require less ionisation energy than those in the s block

Question 4

what is meant by the first ionisation energy ?

Answer 4

the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ atoms

Question 4

what is the ionic equation for first ionisation enegy in terms of lithium ?

Answer 4

Li (g) —-> Li + (g) + e-

Question 5

what is the ionic equation for second ionisation energy in term of lithium atoms ?

Answer 5

Li + (g) —–> Li2+ (g) + e-

Question 6

what is the ionic equation for third ionisation energy in terms of lithium atoms ?

Answer 6

Li2+ (g) ——> Li3+ + e-

Question 7

which ionisation energy is the smallest number ?

Answer 7

first ionisation energy is always the smallest number

Question 8

what is the second ionisation energy in terms of how big the number is ?

Answer 8

• its always larger than the first
• because the electron is taken away from something that is a positive ion so there is greater electrostatic froces of attraction

Question 9

what is the third ionisation energy in terms of how large the number is ?

Answer 9

• the number is larger than first and second ionisation energies because there are even greater electrostatic forces of attraction

Question 10

what is ionisation energies used for ?

Answer 10

• it provides us evidence for the electron shell model
• we can determine the group of the elements

Question 11

why are the last 2 electrons in the second energy level of sodium have higher ionisation energies than the previous 6 ?

Answer 11

because they come from a 3s subshell whilst the previous 6 come from the 2p sub shell
-so they are harder to remove as they are closer to the nucleus and so have greater electrostatic forces of attraction and so require more ionisation energy

Question 12

what do we look at if we want to determine which group the element is in ?

Answer 12

successive ionisation energies

Question 13

what is the overall pattern in successive ionisation energies across period 3 ?

Answer 13

ionisation energy overall increases across period 3

Question 14

state the reasons for an overall increase in IE across period 3 ?

Answer 14

• there is an increased nuclear charge across the period for each element
• atomic radius decreases along period 3
• electrons are in the same energy level so shielding is the exact same across all elements across a period
• so overall there is a stronger attraction between nucleus and the outer electrons

Question 15

explain the cause of the 2 dips in successive ionisation energies across period 3 .

Answer 15

1st dip
- 3s2 to 3p1 outer electron
p sub shell is higher energy level than s sub shell so it is easier to remove
2nd dip
- 3p3 to 3p4
3p3 electrons are unpaired
3p4 1 electron orbital has double occupancy and because of electron repelling, it is easier to remove

Question 16

what is the pattern of successive ionisation energies down group 2 ?

Answer 16

ionisation energies decrease down the group

Question 17

explain why there is a decrease in ionisation energies down a group ?

Answer 17

• atomic radius increases so there is a weaker attraction between outer electron and the nucleus
• shielding increases because there are more energy levels going down the group
• this results in a weaker electrostatic attraction between the nucleus and outer electron