Unit 2 Topic 4A Group 1+2 Flashcards
(40 cards)
Atomic radius down group 2
- increases down the group
- more shells of electrons (atom
Melting points down group 2
- decreases down the group
- metallic bonding weakens as atomic size increases
- distance between positive ions and delocalised electrons increases
- electrostatic attractive force between positive ions and delocalised electrons weaken
1st ionisation energy trend down group 2 elements
- successively further from the nucleus
- outermost electrons held more weakly
- outer shell electrons more shielded from the attraction of the nucleus by the repulsive force of inner shell electrons
Explain the reactivity trend down group 2
- reactivity increases down the group
- atomic radii increase as there is more shielding
- nuclear attraction decreases
- easier to remove outer electrons, cations form more easily
What are the preparations to be done before the reaction with oxygen
- Mg will react slowly with oxygen without a flame
- Mg ribbon will often have thin layer of magnesium oxide on it formed by reaction with oxygen
- 2Mg + O2 -> 2MgO
- needs to be cleaned off by emery paper before doing reactions with Mg ribbon
How to test for the reaction between Mg and acid (why you need to clean the Mg ribbon first)
- an un-cleaned Mg ribbon would give a false result because both the Mg and MgO would react but at different rates.
- Mg + 2HCl -> MgCl2 + H2
- MgO + 2HCl -> MgCl2 + H2O
What are observations when Mg is burnt in oxygen
burns with bright white flame
2Mg + O2 ==> 2MgO
What are something in common of the oxides of group 1 and 2
- usually white solids
- with high melting points due to their ionic bonding
How does magnesium react with water
burns in steam
- to produce magnesium oxide and hydrogen
- burn with bright white flame
react with warm water
- produce magnesium hydroxide and hydrogen
- much slower reaction that the reaction with steam
- no flame
How do other group 1 and group 2 metals beside magnesium react with water
- react with cold water with increasing vigour down the group to form hydroxides (and hydrogen)
Observations of metal hydroxides produced
- fizzing (more vigorous down the group)
- the metal dissolving (faster down the group)
- solution heating up (more down group)
- calcium: produces white precipitate (less down the group)
Why do Mg(OH)2 have lower pH than other metal hydroxides?
- only slightly soluble
- fewer OH- ions are produced
- lower pH value
Reactions of the oxides / hydroxide of group 1 and 2 with acids
salt + water
Solubility trend of group 2 hydroxides down the group
- more soluble down the group
- when not soluble = white precipitates
- less white precipitate down the group
Solubility of group 2 sulfates
- less soluble down the group
- BaSO4 least soluble
Solubility of calcium hydroxide
- reasonably soluble in water
- used in agriculture to neutralise acidic soils
- lime water ==> test for carbon dioxide (turns cloudy)
Barium hydroxide solubility
- easily dissolve
- hydroxide ions present would make the solution strongly alkaline
Thermal decomposition of group 1 and 2 carbonates
- heat to produce oxides and carbon dioxide gas
Thermal stability of group 2 carbonates
- more thermally stable as you go down the group
- cations get bigger
- polarising effect
- distort carbonate ion less
- C-O bond is weakened less ==> less easily breaks down
Define thermal decomposition
- defined as the use of heat to break down a reactant into more than one product
Thermal decomposition of group 1 carbonates
- do not decompose with the exception of lithium
- only have +1 charges
- dont have big enough charge density to polarise carbonate ion
- lithium is exception ==> small enough to have polarising effect
Design experiment to investigate the ease of decomposition
- One is to heat a known mass of carbonate in a side arm boiling tubeand pass the gas produced through lime water.
- Time for the first permanent cloudiness to appear in the limewater.
- Repeat for different carbonates using the same moles of carbonate/same volume of limewater/same Bunsen flame and height of tube above flame.
Thermal decomposition of group 2 nitrates
- decompose on heating to produce group 2 oxides, oxygen, nitrogen dioxide gas
- brown gas evolved (NO2)
- white nitrate solid seen to melt to a colourless solution and then re-solidify
- ease of thermal decomposition decreases down the group (same explanation as carbonates)
Sodium nitrate decomposition
2NaNo3 ==> 2NaNO2 + O2
sodium nitrate (V) ==> sodium nitrate (III)
