topic 3 - first ionisation energy + trends

Question 1

Ionisation energy

Answer 1

First ionisation energy is the amount of energy needed to remove 1 mole of outer electrons from 1 mole of gaseous atoms to form 1 mole of positive ions​
​
X(g) → X+(g) + e-

Question 2

Trends across the periods​

Answer 2

Increase across the period because nuclear charge increases. shielding due to inner shells stay the same

Electrostatic attraction of nucleus + outer electrons increase

Anomiles
group 3 electron removed higher energy sub shell
Group 6 electrons pair up and repel in an orbital

Question 3

Period 2 - Li and Be

Answer 3

In Li and Be the outer electrons are being removed from the 2s orbital​

There is an increase in 1st IE from Li to Be as there are more protons in Be so there is a greater attraction (it is harder to remove the outer electron)

Question 4

Period 2​ - boron

Answer 4

In Boron, the outer electron is being removed from the 2p orbital. ​

This is a higher energy orbital than the 2s so it is shielded by the 2s electrons​

This makes the 2p electron easier to remove so there is a drop in 1st IE

Question 5

Period 2 - Carbon and Nitrogen

Answer 5

In Carbon and Nitrogen, the outer electrons are also being removed from the 2p orbital​

These electrons are unpaired​

These elements show the expected increase in 1st IE due to the increasing nuclear charge​

Question 6

Period 2​ - oxygen

Answer 6

In oxygen, the outer electron is being removed from the 2p orbital BUT it is paired with another electron​

The repulsion between these electrons makes it easier to remove one​

This causes a decrease in 1st IE​

Question 7

Period 2 - Fluorine and Neon

Answer 7

In Fluorine and Neon the outer electrons are also being removed from pairs in the 2p orbital​

They show an increase in 1st IE due to increased nuclear charge

Question 8

Period 3

Answer 8

There is a similar pattern in period 3 1st IE with electrons being removed from the 3s and 3p orbitals

Question 9

Period 4

Answer 9

The pattern in period 4 is similar for groups 1 to 7 and 0, with dips at group 3 and 6​

The 1st IE of the transition metals increases across the period but only slightly as there is a shielding effect from the 3d orbital​

The outer electron from a transition metal always comes from the 4s orbital as this is higher energy than the 3d​

This means the increasing number of 3d electrons provide shielding and cancel out the effect of the additional proton

Question 10

Trends down groups​

Answer 10

As groups descend 1st ionisation energy decreases

Because outer electron being removed further from nucleus there are more inner shells to shield the outer electron

Electrostatic attraction to nucleus is less