More Trends in the Properties of the Elements of Period 3

Question 1

Why are noble gases often left out of atomic radius comparisons?

Answer 1

This is because noble gases do not form covalent bonds and therefore do not have covalent radii

Question 2

Describe the trend in atomic radii down a group, and explain why it occurs

Answer 2

Down a group, atomic radii increases because a new outer main level of electrons is added, which increases the distance between the nucleus and the outer electrons

Question 2

What happens to atomic radius across a period?

Answer 2

Across a period, atomic radius decreases

Question 2

Why does atomic radius decrease across a period?

Answer 2

This is because more protons are added to the nucleus which increases the nuclear charge.

This increase causes the electrons to be pulled closer to the nucleus.

There are no additional electron shells to provide more shielding. so the size of the atom decreases across the period

Question 3

What happens to the number of protons as you move across a period?

Answer 3

The number of protons in the nucleus increases

Question 3

How does increasing nuclear charge across a period affect atomic radius?

Answer 3

Increasing nuclear charge across a period decreases the atomic radius, this is because the outer electrons are pulled closer to the nucleus

Question 4

Why does shielding not increase across a period?

Answer 4

This is because no additional electron shells are added; all new electrons go into the same outer shell

Question 5

Overall, why does atomic radius decrease across a period?

Answer 5

The increased nuclear charge pulls the electrons closer, so without extra electron shell shielding the atomic radius becomes smaller

Question 6

How does first ionisation energy change across a period?

Answer 6

It generally increases across a period from left to right

Question 6

What is the definition of first ionisation energy?

Answer 6

It is the energy required to remove one electron from each atom in a mole of isolated gaseous atoms to form a mole of single positively charged gaseous ions

Question 6

Why does the first ionisation energy increase across a period?

Answer 6

As you move across a period, the number of protons in the nucleus increases, but the electrons enter the same main energy level. The increased nuclear charge makes it harder to remove an electron

Question 6

How does the first ionisation energy change going down a group?

Answer 6

It decreases going down any group

Question 7

Why does ionisation energy decrease as you move down a group?

Answer 7

The number of filled inner electron levels increases, resulting in increased shielding. The outer electron is also further form the nucleus, so it is held less strongly and is easier to remove

Question 8

Why is there a drop in ionisation energy when moving from one period to the next?

Answer 8

There is a sharp drop in ionisation energy when moving from between periods because a new main energy level starts, increasing the atomic radius. The outer electron is further from the nucleus, less strongly attracted, and easier to remove