Chapter 8 (Periodicity)

Question 1

What happens to atomic radius across a period and why?

Answer 1

Decreases due to increase proton number/nuclear charge. This means that there is an increased attraction between the nucleus and electrons, thus are pulled closer the nucleus, making the atomic radius smaller.

Question 2

Explain the trend in melting points across Na, Mg, and Al?

Answer 2

Their melting points increase across the period as the metallic bonds get stronger due to the metal ions having and increasingly positive charge, an increasing positive charge, an increased number of delocalised electrons and a decrease in radius.

Question 3

Why does silicon have a high melting point?

Answer 3

Silicon is macromolecular with a tetrahedral structure, strong covalent bonds hold all it’s atoms together and so a lot of energy is needed to overcome them.

Question 4

Explain the trend in melting points for P, S and Cl ?

Answer 4

They are all molecular substances and so their melting point depends on the strength of their van der waals forces between the molecules. Van der waals forces are weak and so easily overcome, thus they have low melting points. More atoms in a molecule means stronger van der waals forces.

Question 5

What determines the order that elements are arranged in the periodic table?

Answer 5

Proton number

Question 6

Why is aluminium malleable?

Answer 6

There are no direct bonds between metal ions, so they can slide over each other.