4A: elements of group 1 & 2

Question 1

what is the trend of ionisation energy of group 2 elements?

Answer 1

ionisation energy decreases down the group, as there is more shielding between outer e- and nucleus since atomic radii increases

• this overrides the larger nuclear charge

Question 2

what is the trend in reactivity down group 2 elements?

Answer 2

reactivity increases down the group

• more shielding
• lower nuclear attraction therefore easier to remove outer e-

Question 3

how does group 2 elements react with oxygen and what products will be formed?

Answer 3

burn in oxygen
- forms metal oxide

Question 4

how does group 2 elements react with chlorine & what products will be formed?

Answer 4

form metal chloride

Question 5

how does magnesium react with steam?

Answer 5

burn with bright white flame
- forms magnesium oxide & hydrogen

Question 6

how does magnesium react with warm water?

Answer 6

slower reaction than with steam
- forms magnesium hydroxide & hydrogen

Question 7

how does other group 2 metals react with cold water?

Answer 7

forms metal hydroxide

Question 8

describe the vigour down group 2 elements when reacting with cold water.

Answer 8

vigour increases

Question 9

what will be observed when reacting group 2 elements with cold water?

Answer 9

• fizzing
• metal dissolving
• solution heating up
• less white precipitate forming

Question 10

how does group 2 oxides react with water?

Answer 10

oxide ions accept protons & forms hydroxides ions

Question 11

how does group 2 oxides react with acids?

Answer 11

produces salt & water

Question 12

how does group 2 hydroxides react with acids?

Answer 12

produces salt + water

Question 13

describe the trend in solubility of group 2 hydroxides.

Answer 13

solubility increases down the group

Question 14

what colour will insoluble group 2 hydroxides appear? give an example.

Answer 14

white, Mg(OH)2

Question 15

what is the trend of pH values when group 2 oxides react with water?

Answer 15

pH increases as goes down the group

Question 16

what is the trend of solubility of group 2 sulfates?

Answer 16

solubility decreases down the group as it prevents further attack

Question 17

what is thermal decomposition?

Answer 17

using heat to break down a reactant into 1+ products

Question 18

what is the ease of decomposition down group 2 carbonates? why?

Answer 18

ease of decomposition decreases down the group (more thermally stable)
- larger cation has a less polarising effect
-> distorts carbonate ion less & therefore C-O bond less easy to break

Question 19

how does group 1 carbonates decompose?

Answer 19

don’t decompose except Li as 1+ charge is not large enough

Question 20

how could a test for decomposition of carbonates be tested? (4)

Answer 20

1) put a known amount of carbonates in a test tube
2) heat the tube & pass the gas produced through limewater
3) time for the first cloudiness to appear
4) repeat for different carbonates

Question 21

what are some variables that should be controlled when investigating decomposition of carbonates? (4)

Answer 21

• same mol. of carbonates
• same volume of limewater
• same Bunsen flame
• same height of tube above the flame

Question 22

what products are formed when group 2 nitrates decompose?

Answer 22

group 2 oxides, oxygen & nitrogen dioxide

Question 23

what products are formed when group 2 carbonates decompose?

Answer 23

group 2 oxides & carbon dioxide

Question 24

what is the distinctive colour of nitrogen dioxide?

Answer 24

brown

Question 25

what could be observed when group 2 nitrates decompose?

Answer 25

brown gas evolving
white nitrate solid melts & turns colourless & resolidify

Question 26

describe & explain the ease of decomposition down group 2 nitrates.

Answer 26

ease of decomposition decreases down the group
- Mg2+ ion is the smallest & therefore have the greatest polarising power
-> polarises NO3- anion & weakens N-O bond

Question 27

what are the products when group 1 nitrates decompose?

Answer 27

except Li:
nitrate (III) salt & oxygen

Question 28

how does the group 1 nitrate exception decompose?

Answer 28

LiNO3 decomposes like group 2 nitrates
- 4 LiNO3 -> 2 Li2O + 4 NO2 + O2

Question 29

how could a flame test be carried out?

Answer 29

1) use a nichrome wire loop (or unreactive metal)
2) clean the wire by dipping it in conc. HCl & heat in Bunsen flame
3) grind the sample up into powder (if needed)
4) dip the wire in solid & heat it in Bunsen flame

Question 30

how does flame tests show distinctive colours of different cations?

Answer 30

• heat causes e- to move to a higher energy level
• e- is unstable & drops back down
• energy is emitted from the form of visible light