Trends in the Periodic Table

Question 1

What is the covalent radius?

Answer 1

The covalent radius is a measure of the size of an atom (half the distance between the two nuclei of two covalently bonded atoms of an element)
Going across a period - Covalent radius decreases.
Going down a group - Covalent radius increases.

Question 2

Down group

Atomic Size

Answer 2

Down group 1, there are more energy levels. As you move down group 1, the atomic size increases. This is because there are more energy levels causing the outer energy levels to get further away from the nucleus and because of the screening effect, where the inner electrons sheild the outer ones from as much attraction to the nucleus, increasing atomic size.

Question 3

Across a period

Atomic Size

Answer 3

Across period 4, there are more electrons in the outer shells. This is due to there being more eletrons in the outer shells of the atoms and more protons in the nucleus, so the attraction between the positive nucleus and the negative electrons is increasing. This causes the nucleus to pull in the outer shells of the atom, making atomic size smaller.

Question 4

How are Ldfs formed?

Answer 4

They are formed because of temporary dipoles, due to electrons wobble. Electrons are constantly moving, so one side is more negatively charged and one side is positive for a short time, causing Ldfs to form. They are weak beacause the dipoles are temporary.

Question 5

Down a group

Boiling points

Answer 5

As you moved down a group, there are more electron levels. This means more electrons to wobble, so more temporary dipoles, increasing the strength of the Ldfs. This means more energy is needed to LDFs, leading to a increasing boiling.

Question 6

Down a group
Electronegativity
Pretty much the same for ionisation energy.

Answer 6

Down a group the electronegativity decreases. This is because there is more of a sheilding/screening effect between the nucleus and outer electrons due to more electron levels. This causes the outer electron levels to have a weaker attraction, causing the bonding electrons to be further from the nucleus and this decreases electrongegativity.

Question 7

Across a period
Electronegativity
Pretty much the same for ionisation energy.

Answer 7

Across a period the electronegativity increases. This is because there is less of a sheilding/screening effect between the outer electrons and the nucleus, due to more protons in the nucleus attracting the outer leve (greater nuclear charge) l. This attracts the bonding electrons more strongly, increasing electronegativity.

Question 8

How do you answer an explain the trend question?

Answer 8

1. Where electrons come from
2. Stregnth of LDFS
3. Energy required.