Unit 2: Section 1 - Periodicity

Question 1

How are elements in the periodic table arranged?

Answer 1

Elements are arranged according to their proton number

Question 2

What are the 4 blocks of the periodic table?

Answer 2

• s-block
• p-block
• d-block
• f-block

Question 3

What elements are in each block of the periodic table?

Answer 3

• s-block - groups 1 and 2
• p-block - groups 3 to 0
• d-block - transition metals
• f-block - radioactive elements

Question 4

What is periodicity?

Answer 4

The study of trends within the periodic table - often linked to elements’ electronic configurations

Question 5

What is the trend in atomic radius along a period?

Answer 5

Along a period, atomic radius decreases

Question 6

Why does atomic radius decrease along a period?

Answer 6

• Atomic radius decreases due to an increased nuclear charge for the same number of electron shells
• This means that the outer electrons are pulled in closer to the nucleus because the charge produces a greater attraction
• As a result, the atomic radius is reduced

Question 7

What is the trend in atomic radius going down a group?

Answer 7

Going down a group, atomic radius increases

Question 8

Why does atomic radius increases going down a group?

Answer 8

• With each increment down a group, an electron shell is added
• This increases the distance between the outer electrons and the nucleus, reducing the power of attraction
• More shells also increases electron shielding, whereby the inner shells create a ‘barrier’ that blocks the attractive forces
• The nuclear attraction is reduced further and atomic radius increases

Question 9

What is the trend in ionisation energy along a period?

Answer 9

Along a period, ionisation energy increases

Question 10

Why does ionisation energy increases along a period?

Answer 10

• It increases because atomic radius decreases, hence nuclear charge increases
• This means that the outer electrons are held more strongly so more energy is required to remove the outer electron and ionise the atom

Question 11

What is the trend in ionisation energy going down a group?

Answer 11

Going down a group, ionisation energy decreases

Question 12

Why does ionisation energy decrease going down a group?

Answer 12

• The nuclear attraction between the nucleus and outer electrons reduces and shielding also increases
• Both of these factors mean less energy is required to remove the outer electron

Question 13

What does the melting point of period 3 elements depend on?

Answer 13

• The structure of the element
• The bond strength

Question 14

What happens to melting points across period 3 between sdoium and aluminium?

Answer 14

• Sodium, magnesium and aluminium are all metals with metallic bonding - their melting points increase due to the greater positive charge of their ions
• This means more electrons are released in the form of free electrons
• This increases the attractive electrostatic forces from Na to Al, therefore more energy is needed to break them

Question 15

Why does the melting point increase dramatically for silicone in period 3?

Answer 15

• Silicon has a very strong covalent structure
• So more energy is required to break the strong covalent bonds - giving it a very high melting point

Question 16

Why does the melting point decrease in period 3 between phosphorus and chloring?

Answer 16

• Phosphorus, sulphur and chlorine are all simple covalent molecules held with weak van der waals forces
• Less energy is needed to overcome these weak intermolecular forces, so these molecules have relatively low melting points

Question 17

Why does argon have an even lower melting point than chlorine?

Answer 17

• Argon is a noble gas that exists as individual atoms with a full outer shell of electrons
• This makes the atom very stable and the van der waals forces between them very weak
• Less energy is needed to overcome these weak van der waals forces and so argon exists as a gas at room temperature