chapter 8 - periodicity

Question 1

What happens to the atomic radius as you go across a period

Answer 1

The atomic radius decreases across a period

Because nuclear charge increases, there is greater attraction from the nucleus to the outer electrons, shielding remains the same, the outer electron is held in more strongly.

Question 2

What happens to the ionisation energy across period 3

Answer 2

Ionisation energy crossed period three increases

Because the number of protons increase, shielding remains the same and therefore the attraction of the outer electrons to the nucleus increases

Question 3

What is the outlier trend for group 3 elements for ionisation energy and why

Answer 3

In group 3-the 3p orbital is shielded from the S sublevel electrons, therefore the atomic radius increases making the ionisation energy lower than expected.

Question 4

What is the outlier trend for group 6 elements for ionisation energy

Answer 4

Group 6-The P-4 pair of electrons in the P orbital undergoes mutual repulsion so that the electrons are further from the nucleus and therefore easier to remove lowering the ionisation energy done the expected value.

Question 5

Melting point of period three elements

First three elements of period three (sodium, magnesium, aluminium)
(Na, Mg, Al)

What is the trend in melting point for these three elements

Answer 5

Going across the period there is a larger charge and a smaller size of ions. The boiling points and melting points are a measure of the energy required to separate the particles in a substance. Mg2+ ions are larger than Al3+ So aluminium ions are smaller and increase the attraction between the nucleus and the outer electrons giving aluminium a higher melting and boiling points and magnesium and sodium.

Question 6

Melting points and boiling points of period three elements
(silicon)
(Si)

What is the trend for silicone And why does it have such a high melting and boiling point

Answer 6

Silicon is macromolecular, (covalent) a lot of energy is required to break the many strong covalent bonds holding the atoms together.

Question 7

Melting points of period three elements
Last four elements
(Phosphorus, sulfur, chlorine, argon)
(P, S, Cl, Ar)

What is the trend in melting and boiling points for these last four elements in period three

Answer 7

These are all molecular structures (covalent) the larger the molecule the more electrons that are and so the greater the strength of the Vanderwaals forces between molecules. S is the highest (anomaly) as it exists as S8.