2.1 - Periodicity

Question 1

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

Answer 1

The atomic radius decreases because the positive charge of the nucleus increases. This means that the electrons are pulled closer to the nucleus, making the atomic radius smaller. The extra electrons that the elements gain are added to the outer energy level so they don’t really provide any extra shielding

Question 2

What is the general melting point as you go across period 3?

Answer 2

It generally increases from sodium to silicon, and then generally decreases from silicon to argon

Question 3

Why do the melting points of sodium, magnesium and aluminium increase across a period?

Answer 3

Their melting points increase along the period because the metal-metal bonds get stronger. As you go along the group, the ions have an increasing positive charge, an increasing number of delocalised electrons and a decreasing radius

Question 4

Why does silicon have the highest melting point in group 3?

Answer 4

Silicon is macromolecular, with a tetrahedral structure - strong covalent bonds link all of the atoms together. A lot of energy is needed to break these bonds

Question 5

What intermolecular force links to the melting points of phosphorous, sulphur, chlorine and argon?

Answer 5

Van der Waals forces. More atoms means stronger van der Waals forces and as sulphur is the biggest, it has the highest melting point, followed by phosphorous and chlorine. Argon has a very low melting point due to it being monatomic

Question 6

What is the trend of first ionisation energies across a period?

Answer 6

The general trend in ionisation energy is that it increases due to the increasing attraction between the outer shell electrons and the nucleus due to the number of protons increasing