6.2 group 2 & 17 elements

Question 1

does reactivity increase or decrease down group 2 and why?

Answer 1

increase. down the group,
- number of electronic shells increases, higher principal quantum number, leading to an increase in screening effect
- valence electrons are increasingly further away from the nucleus and are less strongly attracted, despite the increase in nuclear charge
- smaller amount of energy needed to remove the valence electron

Question 2

does thermal stability of metal carbonates increase or decrease down the group?
(hint: thermal stability of carbonates is influenced by size of anion and charge density of cation, and CO3 2- needs to break to form CO2)

Answer 2

increase. down the group,
- ionic radius of cation increases
- charge density of cation decreases
- polarising power of cation decreases
- extent of distortion of CO3 2- electron cloud decreases
- extent of weakening of covalent bonds within CO3 2- decreases
- thermal stability of carbonates increases.

Question 3

are group 2 carbonates more or less thermally stable than group 1 carbonates?

Answer 3

less thermally stable because of the greater polarising power of the group 2 cation which polarises the CO3 2- anion to a greater extent

Question 4

how does volatility change down group 17?

Answer 4

volatility decreases down group because volatility is inversely proportional to boiling points, which is proportional to strength of id-id interactions, which is proportional to size of group 17 atoms

Question 5

how does strength as oxidising agents change down group 17?
(hint: oxidising requires the halogen to gain electrons)

Answer 5

strength of oxidising agents decreases down the group because electronegativity decreases down group, where electronegativity represents the ease of gaining electrons. valence electrons are increasingly further from the nucleus and hence less strongly attracted

thus Cl and Br oxidise S2O 3- to SO4 2- while I only oxidises S2O3 2- to S4O6 2-