8.1 Group 2 Metals Flashcards
Why do melting points decrease down a group?
Atomic radius increases which weakens metallic bonding, electrostatic forces weaken between cations and the delocalised electrons/bonding electron.
What do all group 2 metals have as their outer shell configuration?
S2
What is the reacitvity down a group?
Reactivity increases down a group, as ionisation energies decrease.
The first ionisation energy is the energy required to remove the first outer electron of an atom.
The second ionisation energy is the energy needed to remove the second outer electron of an atom.
As atomic radii increases, there is more sheilding. Therefore, the electrostatic attraction between the nucleus and outer/valent electrons decrease and its easier to remove an electron (first ionisation energy- energy required to remove one outer electron)
When group 2 elements react they lose electrons to form 2+ ions. The easier it is to lose electrons/donate , the more reactive the element so reactivity increases down the group.
What is the reaction of group 2 metals with oxygen?
They will burn in oxygen to produce a bright white flame.
2Mg (s)+ O2 (g)—-> 2MgO (s) white solid that has a high MP due to its ionic bonding)
- +2. -2
M—> M2+ + 2e-
Sr and Ba form peroxide MO2 too
How does magnesium/group 2 metals react with water? Abd steam
They react with water to form an alkaline metal hydroxide with a general formula M(OH)2 and hydrogen gas.
Water and magnesium react slowly, the reaction is more vigorous down the group.
Barium and radium are most reactive.
M (s) + 2H20 (l) —-> M(OH)2 (s) + H2 (g)
0. +2
This is an example of a redox reaction. Be is not reactive w water.
More hydrogen bubbling down group 2
What is the reaction group 2 metals with dilute acids? (Hydrochloric acid)
Metal + acid —-> salt + hydrogen
When group 2 metals react with dilute HCl you get a colourless metal chloride and hydrogen gas
M (s) + 2HCl (aq) ——> MCl2 (aq) + H2 (g)
0. +1. +2. 0
Group 2 metals with dilute acids reactions is more vigirous downn the group/more alkaline solutions produced down group 2
Insoluble sulfate formed when metal reacts with sulfuric acid.
M + HSO4 (aq) —-> M(SO4) (aq) + H2 (g)
group 2 sulfates are less soluble down group 2
What will a person observe as the hydroxides make the water alkaline?
- fizzing (more vigorous down group)
- the metal dissolving
- solution heats up
- with calcium a white precipitate forms
What happens when you react an oxide of a group 2 element (like CaO) with water?
Group 2 oxides and hydroxides are bases so are soluble in water.
CaO + H20 (l) ——> Ca 2+ (aq) + 2OH-
These hydroxide ions are released into the solution which increase the pH. They form alkaline solutions of the metal hydroxide.
CaO + H20 —-> Ca 2+ + 2OH-
Ca2+ + 2OH- (aq) —-> Ca(OH)2 (aq)
Any further metal and hydroxide ions will form a solid precipitate
Calcium hydroxide is limewater in solution
What happens when the solution becomes saturated? (And what is the equation?)
Group 2 hydroxides are only slightly soluble in water. When the solution becomes saturated, any further metal and hydroxide ions will form a solid precipiate.
Ca2+ (aq) + 2OH- (aq) —-> Ca(OH)2 (s)
What is the solubility of hydroxides in water down the group?
As we go down the group 2, solubillity of hydroxides increases. This is because resulting solutions contain a greater concentration of OH- (aq) ions are released into the solution and therefore are more alkaline.
O2- + H20 —-> 2OH- (aq)
How can we show the hydroxide solubility increases?
- Add spatula of each group 2 oxide to water in test tube.
- Shake the mixture- there is insufficent water to dissolve all the metal hydroxide that forms. Therefore we are left with a saturated solution.
- Measure the pH of each solution. The alkalinity increases down the group.
What is the use of group 2 compounds in agriculture?
Calcium hydroxide ( Ca(OH)2 ) is added to fields to increase the pH of acidic soils. Calcium hydroxide neutralises acid in soil, forming neutral water.
Ca(OH)2 (s) + 2HCl (aq)——> 2H2O (l) + MgCl2 (aq)
H+ (aq) + OH- (aq)—-> H2O (l)
Raises pH of soil to optimum 6.5
What is the use of group 2 compounds in medicine?
Often used as antacids for treating acid indigestion. Use magnesium and calcium carbonates- milk of magnesia is a suspension of white magnesium hydroxide Mg(OH)2 in water. The acid in our stomach is mainly HCl and neutralisation reactions take place.
Mg(OH)2 + 2HCl (aq) ——> MgCl (aq) + 2H2O (l)
2CaCO3 (s) + 2HCl (aq)——> CaCl2 (aq)+ H20 (l) + CO2 (g)
Why are group 2 elements described as reducing agents?
Each element in group 2 has 2 electrons in its outer shell, losing them to form 2+ ions. Therefore, it has been oxidised. Another species will gain these electrons and be reduced. The group 2 element is a reducing agent bcz it has reduced another species
What are group 2 metals known as?
Alkali earth metals
