Periodic Table Trends - HQ

Question 1

What happens to the elements as we move across periods? (Left to right)

Answer 1

• First ionisation energy increases
• Electronegativity increases
• Atomic radius decreases

Question 2

Why does atomic radius decrease across periods?

Answer 2

The number of protons increases, with the same number of inner shell electrons. This leads to an increase in core charge due to a stronger electrostatic attraction between the most loosely bound electrons and the nucleus, therefore the most loosely bound electrons are closer to the nucleus, causing a decrease in atomic radius.

Question 3

Why is there an increase in first ionisation energy across periods?

Answer 3

As we move along a period (i.e. across groups), the core charge increases. As a result, it will be more difficult to remove an electron from the atoms with the larger atomic numbers (or larger core charges) in a particular period, and thus there is an
increase in first ionisation energy.

Question 4

Define

Electronegativity

Answer 4

The electron-attracting power of an atom in a molecule.

Question 5

Why does electronegativity increase across a period?

Except noble gases

Answer 5

The atom radius decreases, so an incoming electron can approach the nucleus more closely. The core charge increases, so the incoming electron is attracted more strongly. Thus the electronegativity increases.

Question 6

What happens to elements as we move down a group?

Answer 6

• First ionisation energy decreases
• Electronegativity decreases
• Atomic radius increases

Question 7

Why does the atomic radius increase down a group?

Answer 7

When going down a group, there is an additional shell further from the nucleus, therefore the most loosely bounded electrons are further away from the nucleus, causing an increase in atomic radius.

Question 8

Why does the first ionisation energy decrease down a group?

Answer 8

There is an additional shell further from the nucleus, thus the most loosely bounded electron is further from the nucleus, so less energy will be required to remove it, causing a decrease in first ionisation energy.

Question 9

Why does electronegativity decrease down a group?

Answer 9

Atomic radius increases down a group, so the incoming electron cannot approach the nucleus as closely, so there is a weaker electrostatic attraction between the incoming electron and the nucleus, causing a decrease in electronegativity.