Inorganic - Group 2, the Alkaline Earth Metals Flashcards
What are the alkaline earth metals?
The elements in group 2 are sometimes called the alkaline earth metals. This is because their oxides and hydroxides are alkaline. Like Group 1, they are s-block elements. They are similar in many ways to Group 1 but they are less reactive. Beryllium is not typical of the group.
How does electron arrangement change in Group 2?
- the elements all have two electrons in an outer s-orbital
- this s-orbital becomes further away from the nucleus going down the group
How do the sizes of the atoms change in Group 2?
- the atoms get bigger going down the group
- the atomic (metallic) radii increase because each element has an extra filled main level of electrons compared with the one above it
How does the melting point change in Group 2?
- they are metals with high melting points, typical of a giant metallic structure
- going down the group, the electrons in the ‘sea’ of delocalised electrons are further away from the positive nuclei
- as a result, the strength of the metallic bonds decreases going down the group as the attractive force has to act over a much greater distance
- for this reason, the melting points of Group 2 elements decrease slightly going down the group
- magnesium doesn’t fit the trend because its crystal structure changes, so less energy is required
How do ionisation energies change in Group 2?
- in all their reactions, atoms of elements in Group 2 lose their two outer electrons to form ions with two positive charges
- so an amount of energy equal to the sum of the first and the second ionisation energies is needed for complete ionisation
- both the first and second ionisation energy decrease doing 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
Are Group 2 metals oxidised or reduced in their reactions?
Oxidation is loss of electrons so in all their reactions, the Group 2 metals are oxidised. The metals go from oxidation state 0 to oxidation state +2. These are redox reactions.
What happens when beryllium reacts with water/steam?
Beryllium is the only alkaline earth metal that does not react with water. This is due to its small size and high ionisation energy in relation to the other elements in the group.
What happens when magnesium reacts with water?
- Mg(s) + 2H2O(l) -> Mg(OH)2(s) + H2(g)
- slow reaction
- sparingly soluble Mg(OH)2 / insoluble
- if warmed, some effervescence
What happens when magnesium reacts with steam?
- Mg(s) + H2O(g) -> MgO(s) + H2(g)
- test tube filled with rocksilk wool soaked with water and heated
- reacts faster as it provides the reaction with extra energy
- bright white light
- hydrogen is flammable
- magnesium oxide is a white powder
What happens when calcium reacts with water?
- Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g)
- reacts faster
- slightly soluble
- bubbling, effervescence
- white solid, uncoloured because not transition metal
What happens when strontium reacts with water?
- Sr(s) + 2H2O(l) -> Sr(OH)2(aq) + H2(g)
- reacts more rapidly
- more soluble
- colourless solution
- effervescence
What happens when barium reacts with water?
- Ba(s) + 2H2O(l) -> Ba(OH)2(aq) + H2(g)
- even more rapid reaction
- soluble
- colourless solution
- effervescence
How does reactivity change down the group?
- increases down the group
- atoms get bigger
- more shielding
- easier to lose two outer shell electrons
- attraction between outer shell electrons and positively charged nucleus weakens
What is the trend in solubility of group 2 hydroxides?
There is a clear trend in the solubilities of the hydroxides - going down the group they become more soluble. The hydroxides are all white solids.
How soluble is magnesium hydroxide?
Magnesium hydroxide (milk of magnesia) is almost insoluble. It is a solid as a suspension in water, rather than a solution.
Mg 2+ (aq) + 2OH - (aq) -> Mg(OH)2 (s)
