Topic 14 - Group 2, The Alkaline Earth Metals Flashcards
What’s the trend in atomic radius down group 2 from Mg-Br?
Atomic radius increases down the group.
- An increasing number of shells, so is more shielding
- hence, less attraction of the nucleus for the outer electrons, and so the atoms increase in size.
What’s the trend in first ionisation energy down group 2, Mg-Ba?
First ionisation decreases down group 2
- increase in atomic radius because of more shells of electrons
- there is more shielding of the outer electron from the nuclear charge
- as a result, less nuclear attraction to outer electron.
What’s the trend in melting point down group 2, from Mg-Ba?
The melting point of the elements decrease down the group.
- group 2 metals have metallic bonding
- going down the group there are more shells of electrons and the metallic cations get bigger in size
- hence, the delocalised electrons are further away from the positive nucleus and attraction between positive cations and the delocalised electrons decreases
- hence metallic bonds are weaker and require less energy to break
What are the Reactions of group 2 metals with water
M + 2H2O —> M(OH)2 + H2
- Mg reacts slowly with cold water
- Ca, Sr and Ba react readily with water
What are the Observations for Ca,Sr and Ba reaction with water?
- heat is released (exothermic)
- bubbles are produced
- metal disappears
- colourless solution formed
- reaction increases in vigour as go down group
What is the reaction of magnesium with steam?
Mg + H2O(g) —> MgO + H2
- magnesium burns with a white light and a white powder is produced
Describe the relative solubilities of the of the group 2 hydroxides, from Mg-Ba
As you go down the group the solubility of the group 2 hydroxides increases.
- magnesium hydroxide is virtually insoluble
- barium hydroxide is soluble
What’s the use of magnesium hydroxide?
Used in medicine.
- magnesium hydroxide is used as an antacid in indigenisation tablets to neutralise excess acid in the stomach and relieve indigestion.
What’s the use of calcium hydroxide?
Used in agriculture.
- calcium hydroxide is used to help reduce soil acidity.
Describe the relative solubilities of the group 2 sulfates, from Mg-Ba
Solubility decreases as you go down group 2
- magnesium sulfate - soluble
- barium sulfate - insoluble
What’s the use of Barium sulfate?
Used in medicine.
- can be taken as a barium meal to outline the stomach or intestines during x-rays.
- barium is opaque to X-rays
- barium compounds are toxic, but it is safe to use in this way as barium sulfate is insoluble.
Describe and explain the use of acidified barium chloride.
Is used to test for the sulfate ion.
Add BaCl2 to sample, If a white precipitate is formed then the substance must contain a sulfate. The precipitate is insoluble barium sulfate.
Ba 2+(aq) + SO4 2-(aq) —> BaSO4(s)
Why should the solution be acidified?
The barium chloride solution must acidified with HCl or HNO3 to remove any carbonate ions.
Barium carbonate is a white insoluble solid that would be indistinguishable from barium sulfate
What’s the use of magnesium in extraction of titanium?
Titanium (v) chloride can be reduces with magnesium, at a temperature of around 700 degrees, to produce titanium metal.
TiCl4 + 2Mg —> Ti + 2MgCl2
Describe the use of CaO and CaCO3 to remove SO2 from flue gasses
Flue gases from burning of coal in a power station will pass through a spray of finely ground calcium carbonate or calcium oxide suspended in water and the acidic sulfur dioxide will react with them.
- CaCO3 + SO2 —> CaSO3 + CO2
- CaO + SO2 —> CaSO3
