7.2 Ionisation Energies

Question 1

What is first ionisation energy?

Answer 1

energy required

to REMOVE 1 ELECTRON

from EACH ATOM

in 1 MOLE of GASEOUS ATOMS

to form 1 MOLE of GASEOUS 1⁺ IONS

Question 2

What are the factors affecting ionisation energy?

Answer 2

ATOMIC RADIUS

NUCLEAR CHARGE

NUMBER OF SHELLS

Question 3

How does increasing ATOMIC RADIUS affect ionisation energy?

Answer 3

￪ atomic radius =

• weaker electrostatic attraction between electrons + nucleus
• Outer electrons require less energy to remove
• Less endothermic ionisation energy

Question 4

How does increasing NUCLEAR CHARGE affect ionisation energy?

(moving across period)

Answer 4

￪ nuclear charge =

• more protons in nucleus
• stronger electrostatic attraction between electrons + nucleus
• Outer electrons require more energy to remove

Question 5

How does increasing the SHELL NUMBER affect ionisation energy?

Answer 5

￪ number of shells =

• greater shielding effect
• more repulsion of outer electrons by inner shells
• weaker electrostatic attraction between outer electrons + nucleus
• Outer electrons require less energy to remove

Question 6

Which effect is greater, nuclear charge or shielding?

Answer 6

shielding

Question 7

Is ionisation energy always exothermic or endothermic and why?

Answer 7

endothermic

energy must be put into system

in order to overcome electrostatic attraction to remove electron

Question 8

Across a period, ionisation energy generally increases, why?

Answer 8

￪ no. of protons

￪ nuclear charge

same shielding

stronger electrostatic attraction of outer electrons to nucleus

￬ atomic radius

Question 9

If element A has a greater nuclear charge than element B, element B will have a _____ ionisation energy IF A has more shells.

Answer 9

higher

Question 10

Across a period, ionisation energy generally _____.

this means different things for reactivity depending on whether the element reacts by gaining or losing an electron.

Answer 10

increases

Question 11

_____ electrostatic attraction of outer electrons to nucleus = high ionisation energy

Answer 11

strong

Question 12

_____ electrostatic attraction of outer electrons to nucleus = low ionisation energy

Answer 12

weak

Question 13

For metals, a low ionisation energy means a _____ reactivity. Explain this trend.

Answer 13

high

react by losing electrons

if electrostatic attraction is weak + ionisation energy is low,

electrons are more easily lost

Question 14

Is the 2nd ionisation energy higher or lower than the first? Why?

Answer 14

higher

after first electron lost, atom is 1⁺ cation & same amount of positive charge attracting less negative charge

stronger electrostatic attraction of outer electrons to nucleus

requires more energy to remove

Question 15

2nd ionisation energy is _____ than 1st.

Answer 15

greater

Question 16

What do successive ionisation energies give an indication of?

Answer 16

GROUP of the element

Question 17

How can you tell the group of an element based on it’s successive ionisation energies?

Answer 17

successive ionisation energies increase because of cation formation

LARGE JUMP = electron being removed from lower shell

Question 18

Why does taking an electron from a lower shell have a significantly larger ionisation energy?

Answer 18

lower shell = closer to nucleus

STRONGER ELECTROSTATIC ATTRACTION of outer electrons to nucleus

more ENERGY REQUIRED to overcome electrostatic attraction + remove electron

Question 19

Why is the ionisation energy of group 3 less than group 2?

Answer 19

electron in group 3 is in 2p orbital

further from nucleus

weaker electrostatic attraction

requires less energy to remove than 2nd electron

Question 20

Why is the ionisation energy of group 6 less than group 5?

Answer 20

electron in group 6 is the first in the p block to share an orbital with another electron

repulsion within orbital

requires less energy to remove than 5th electron (which does not share an electron)

Question 21

More reactive metals have a _____ ionisation energy.

Answer 21

lower

(react by losing electrons, more easily lost if ionisation energy is lower)