4A: elements of group 1 & 2 Flashcards
what is the trend of ionisation energy of group 2 elements?
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
what is the trend in reactivity down group 2 elements?
reactivity increases down the group
- more shielding
- lower nuclear attraction therefore easier to remove outer e-
how does group 2 elements react with oxygen and what products will be formed?
burn in oxygen
- forms metal oxide
how does group 2 elements react with chlorine & what products will be formed?
form metal chloride
how does magnesium react with steam?
burn with bright white flame
- forms magnesium oxide & hydrogen
how does magnesium react with warm water?
slower reaction than with steam
- forms magnesium hydroxide & hydrogen
how does other group 2 metals react with cold water?
forms metal hydroxide
describe the vigour down group 2 elements when reacting with cold water.
vigour increases
what will be observed when reacting group 2 elements with cold water?
- fizzing
- metal dissolving
- solution heating up
- less white precipitate forming
how does group 2 oxides react with water?
oxide ions accept protons & forms hydroxides ions
how does group 2 oxides react with acids?
produces salt & water
how does group 2 hydroxides react with acids?
produces salt + water
describe the trend in solubility of group 2 hydroxides.
solubility increases down the group
what colour will insoluble group 2 hydroxides appear? give an example.
white, Mg(OH)2
what is the trend of pH values when group 2 oxides react with water?
pH increases as goes down the group
what is the trend of solubility of group 2 sulfates?
solubility decreases down the group as it prevents further attack
what is thermal decomposition?
using heat to break down a reactant into 1+ products
what is the ease of decomposition down group 2 carbonates? why?
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
how does group 1 carbonates decompose?
don’t decompose except Li as 1+ charge is not large enough
how could a test for decomposition of carbonates be tested? (4)
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
what are some variables that should be controlled when investigating decomposition of carbonates? (4)
- same mol. of carbonates
- same volume of limewater
- same Bunsen flame
- same height of tube above the flame
what products are formed when group 2 nitrates decompose?
group 2 oxides, oxygen & nitrogen dioxide
what products are formed when group 2 carbonates decompose?
group 2 oxides & carbon dioxide
what is the distinctive colour of nitrogen dioxide?
brown
what could be observed when group 2 nitrates decompose?
brown gas evolving
white nitrate solid melts & turns colourless & resolidify
describe & explain the ease of decomposition down group 2 nitrates.
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
what are the products when group 1 nitrates decompose?
except Li:
nitrate (III) salt & oxygen
how does the group 1 nitrate exception decompose?
LiNO3 decomposes like group 2 nitrates
- 4 LiNO3 -> 2 Li2O + 4 NO2 + O2
how could a flame test be carried out?
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
how does flame tests show distinctive colours of different cations?
- 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
