2.1- Periodicity

Question 1

What is the definition of periodicity

Answer 1

Periodicity is the repeating pattern of physical or chemical properties going down across the periods

Question 2

How does atomic radius change across a period

Answer 2

Atomic radii decrease form left to right across a period as there is an increased number of protons that create a more positive charge attraction for electrons which are in the same shell with similar shielding

Question 3

What is the trend for 1st ionisation energy down a period and give the exceptions in period 3

Answer 3

There is a general trend across a period to increase, this is due to the increasing nubers of protons as electrons are being added to the same shell

In period 3 there is a a drop between Mg and Al, as Mg has its outer electrons in the 3s orbital, but Al is starting to fill out the 3p orbital, this would be slightly easier to remove as the 3p orbitals are slightly higher energy

There is also a small drop between phosphorous and sulfurm as the sulfurs outer electron is being paired up with another electron in the same 3p orbital, when the second electron is added to the orbital there is a slight repulsion between these 2 negative electrons which makes the second electron easier to remove

Question 4

Describe the melting and boiling points for the period 3 metals and explain the reasons for them

Answer 4

For Na, Mg and Al there is srong bonding that gets stronger the more electrons that are in the outer shell, this is because they get released into the sea of delocalised electrons and a smaller sized ion with a greater positive charge also makes the bonding stronger, there is higher energy needed to break the bonds

Question 5

Describe the melting and boiling point for Si and explain the reasons for it

Answer 5

Si is macromolecular, hence there are many strong covalent bonds between the atoms, there is a high energy needed to break the covalent bonds which gives it a very high melting and boiling point

Question 6

Describe the melting points for the period 3 non metals, and explain ther reasons for this

Answer 6

Cl2, S8 and P4 are all simple molecular molecules, they are held together by weak van der waals forces between the molecules, there is little energy needed to break them

S8 has a higher boiling point than P4 because tehre are more electrons so it has stronger van der waals forces between the molecules

Ar is monoatomic and has weak van der waals between its atoms