2.2 Group 2 - Alkaline earth metals Flashcards
Why is the trend in atomic radius down the group?
Atomic radius increases down the group.
As one goes down the group, the atoms have more shells of electrons making the atom bigger.
What is the trend in melting point down the group?
Melting points decrease down the group. The metallic bonding weakens as the atomic size increases. The distance between the positive ions and delocalised electrons increases. Therefore the electrostatic attractive forces between the positive ions and the delocalised electrons weaken. For this reason the mp of Group 2 elements decreases slightly going down the group.
What is the trend in 1st and 2nd ionisation energy down group 2?
Both decrease down the group- it takes less energy to remove the electrons as they become further and further away from the positive nucleus. the nucleus is more effectively shielded by more inner shells of electrons.
What happens to reactivity down group 2?
Reactivity of group 2 metals increases down the group.
How do Group 2 elements react with oxygen?
The group 2 metals will burn in oxygen. Mg burns with a bright white flame. The MgO appears as a white powder.
2 Mg + O2 –> 2 MgO
MgO is a white solid with a high melting point due to its ionic bonding.
How else does mMg react with Oxygen?
Magnesium will also react slowly in oxygen without a flame. Magnesium ribbon will often have a thin layer of magnesium oxide on it formed by the reaction with oxygen in the air.
2 Mg + O2 2 MgO
The magnesium oxide needs to be removed by emery paper before doing reactions with magnesium ribbon.
If testing for reaction rates with Mg and acid, an un-cleaned Mg ribbon would give a false result because both the Mg and MgO would react but at different rates.
Mg + 2 HCl —> MgCl2 + H2
MgO + 2 HCl —> MgCl2 + H2O
How does Mg react with STEAM?
Magnesium reacts in steam to produce magnesium oxide and hydrogen. The Mg would burn with a bright white flame. The MgO appears as a white powder.
Mg(s) + H2O(g) —> MgO(s) + H2(g)
How does Mg react with warm water?
Mg will also react with warm water, giving a different magnesium hydroxide product.
Mg + 2 H2OMg(OH)2 + H2
This is a much slower reaction than the reaction with steam and there is no flame.
How do other group 2 metals, not Mg, react with cold water?
The other group 2 metals will react with cold water with increasing vigour down the group to form hydroxides.
Ca + 2 H2O (l) —> Ca(OH)2 (aq) + H2 (g) Sr + 2 H2O (l) —> Sr(OH)2 (aq) + H2 (g) Ba + 2 H2O (l) —> Ba(OH)2 (aq) + H2 (g)
The hydroxides produced make the water alkaline (if they are soluble in water).
What would you observe from the reaction with cold water and Group 2 elements?
One would observe:
fizzing, (more vigorous down group)
the metal dissolving, (faster down group)
the solution heating up (more down group)
with calcium a white precipitate appears (less precipitate forms down group with other metals)
Why is Titanium useful and what is it used for?
Titanium is a very useful metal because it is abundant, has a low density and is corrosion resistant – it is used for making strong, light alloys for use in aircraft.
Why can titanium not be extracted with carbon or by electrolysis?
Titanium cannot be extracted with carbon because titanium carbide (TiC) it is formed rather than titanium.
Titanium cannot be extracted by electrolysis because it has to be very pure.
What are the steps in extracting titanium?
- TiO2 (solid) is converted to TiCl4 (liquid) at 900 degree C:
- The TiCl4 is purified by fractional distillation in an argon atmosphere.
- The Ti is extracted by Mg in an argon atmosphere at 500 degree C
What are the equations for the extractions of titanium?
TiO2 +2Cl2 +2C —> TiCl4 +2CO
TiCl4 + 2Mg —> Ti + 2 MgCl2
Why is titanium oxide converted to Titanium Tetrachloride?
TiO2 is converted to TiCl4 as it can be purified by fractional distillation, TiCl4 being molecular (liquid at room temperature) rather than ionic like TiO2 (solid at room temperature).
