Unit 3.1.4 - Periodicity

Question 1

What three blocks is the periodic table split into?

Answer 1

s, p and d

Question 2

In what order to the blocks in the periodic table go?

Answer 2

s then d and then p

Question 3

Where do all things in the s block of the periodic table have in common?

Answer 3

The outer most sub level is the s sub shell

Question 4

What is the trend in atomic radius across period 3?

Answer 4

The atomic radius decreases

Question 5

Why does the atomic radius decrease as you go along period 3?

Answer 5

The number of protons increase meaning the nuclear charge increases, however the shielding remains similar, this means the electrons are pulled closer to the nucleus making the atomic radius smaller

Question 6

What is the general trend in first ionisation energies as you go along period 3?

Answer 6

The first ionisation energy generally increases

Question 7

Why does the first ionisation generally increase as you go along period 3?

Answer 7

As the nuclear charge increases the attraction between the outer shell electrons and the nucleus increases meaning they require more energy to remove then, increasing the first ionisation

Question 8

Which two elements deviate from the general trend of decreasing first ionisation along period 3?

Answer 8

Aluminium and sulphur

Question 9

Why does the first ionisation energy decrease between magnesium and aluminium in stead of increasing?

Answer 9

In magnesium the outer electron is in the 3s orbital but in aluminium it is in the 3p orbital. As 3p is further away from the nucleus and there is more shielding there is less attraction to the outermost electron and so it is easier to remove decreasing the first ionisation energy

Question 10

Why does the first ionisation energy decrease between phosphorus and sulphur instead of increasing?

Answer 10

In phosphorus the outermost 3p electron is unpaired however in sulphur the outermost 3p electron is shared. As it is shared there is electron repulsion in the orbital and so the electron is easier to remove decreasing the first ionisation energy

Question 11

What is the general trend in the melting points along period 3?

Answer 11

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

Question 12

Why do the melting points increase along period 3 between sodium and aluminium?

Answer 12

The metal bonds get stronger with the increasing number of delocalised electrons and decreasing radius. This attracts the ions together more strongly and so require more energy to overcome increasing the melting point

Question 13

Which element in period 3 has the highest melting point?

Answer 13

Silicon

Question 14

Why does silicon have the highest melting point along period 3?

Answer 14

It forms a giant covalent structure and so has strong covalent bonds between all the atoms which require a lot of energy to break increasing the melting point

Question 15

Why do phosphorus, sulphur, chlorine and argon has relatively low melting points compared to the other elements in period 3?

Answer 15

They only form simple molecular structures

Question 16

What does the melting point of the elements on period 3 from phosphorus to argon depend on?

Answer 16

The size of the molecule and the strength of the Van der Waals forces

Question 17

What molecules do phosphorus, sulphur, chlorine and argon form and so which one had the highest melting point?

Answer 17

P4, S8, Cl2 and argon exists as individual atoms

Sulphur has the highest melting point out of these elements because it forms the biggest molecule

Question 18

What is the general trend in electronegativity along period 3?

Answer 18

Electronegativity increases along period 3

Question 19

Why does electronegativity increase along period 3?

Answer 19

There is similar shielding and more protons as you go along the group meaning a greater nuclear charge to attract the electrons in a covalent bond