ionisation energies

Question 1

define: ionisation energy

Answer 1

the energy required to remove an electron from an element to form a positive ion

Question 2

define: first ionisation energy

Answer 2

the energy required to remove one mole of electrons

from one mole of gaseous atoms

to form one mole of gaseous positive ions

Question 3

write the equation for the first ionisation energy of an element

Answer 3

X(g) —> X+(g) + e-

Question 4

the ionisation energy generally …………… across a period

why?

Answer 4

increases

• there are more protons in the nucleus
• there is no additional shielding
• there is a greater attraction to the outer electron

Question 5

in period 3 where is the first dip in the pattern?

why is less energy required to remove the electron from aluminium?

Answer 5

between magnesium and aluminium

• the outer electron from Al is removed from the 3p orbital
• which is further from the nucleus

Question 6

where is the first dip in period 2?

explain why boron has a lower first ionisation energy than beryllium?

Answer 6

between beryllium and boron

• the outer electron in B is removed from the 2p orbital
• which is further from the nucleus

Question 7

where is the second dip in period 3?

why is less energy required to remove the electron from sulphur?

Answer 7

between phosphorus and sulphur

• there is a pair of electrons in the 3p orbital
• this causes repulsion

Question 8

where is the second dip in period 2?

why does oxygen have a lower first ionisation energy than nitrogen?

Answer 8

between nitrogen and oxygen

oxygen has a pair of electrons in the 3p orbital this causes repulsion

Question 9

the ionisation energy ………….. down a group

why?

Answer 9

decreases

• the outer electron is further from the nucleus
• there is increased shielding

Question 10

explain why sodium has a higher first ionisation energy than potassium

Answer 10

the electrons are removed from a lower principle energy level

which is closer to the nucleus

there is less shielding

Question 11

define: second ionisation energy

Answer 11

the energy needed to remove a second electron

from each ion in a mole of gaseous ions

Question 12

write an equation to show the second ionisation energy of an element

Answer 12

X+(g) —> X2+(g) + e-

Question 13

write an equation to show the third ionisation energy of an element

Answer 13

X2+(g) —> X3+(g) + e-

Question 14

why does the ionisation energy increase when you remove successive electrons?

Answer 14

the electron is removed from a positive ion

which attracts the electron more strongly

Question 15

why is there a large increase in the third ionisation energy compared to the second and first ionisation energies?

Answer 15

The third electron is being removed from a lower principal energy level

which is closer to the nucleus

and there’s less shielding

Question 16

The atomic radius …………… across a period

Why?

Answer 16

decreases

There is an increase in positive nuclear charge

So there is a greater attraction between the nucleus and outer shell electrons