3.2.2 Group 2, the alkaline earth metals
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What is the trend in first ionisation energy of group 2?
It decreases down the group This is because the electron is further from the nucleus so there is less attraction and increased shielding
What is the trend in boiling point of group 2?
It decreases down the group The distance between the delocalised sea of electrons and the nucleus increases This decreases the strength of the metallic bond as electrostatic attraction is weaker
Which group 2 element does not follow the trend in boiling points?
Magnesium
What is the trend in atomic radius of group 2 elements?
It increases as you go down the group Atoms get bigger because each element has another shell full of elements
What is the equation for the reaction between beryllium and water? What are the conditions?
Be + H2O = BeO + H2 High temperatures
What is the equation for the reaction between magnesium and water? What are the conditions?
Mg + H2O = MgO + H2 Reacts rapidy with steam
What is the trend in reactivity of group 2 elements with water?
Increase in reactivity Can react with cold water, to form hydrogen gas and hydroxide: redox reactions
What is a non-medical use of barium chloride?
It’s solubility is also useful when testing for sulfate ions in a solution It allows a precipitate of barium sulfate to form indicating the completion of the reaction
Why is magnesium hydroxide suitable for ingestion as a digestive medication?
It is a weak base so is non-toxic which allows it to be consumed in small quantities
How does magnesium hydroxide and calcium hydroxide compare in terms of strength? What use does this make calcium hydroxide suitable for?
Calcium hydroxide is a stronger base Agriculture to adjust the pH of acidic soil and lakes
What is rutile?
Titanium ore
What is the equation for the reaction between titanium ore and chlorine? Why does the product of this reaction have to undergo fractional distillation?
TiO2 + 2Cl2 + 2C = TiCl4 + 2CO To seperate titanium chloride from the other chlorides A range of metal chlorides are formed because there are other metal chlorides in the ore
What are the reaction conditions for the reaction between titanium (IV) chloride and magnesium?
Molten magnesium Titanium (IV) chloride vapour
Why is dilute hydrochloric acid added after the reaction between titanium (IV) chloride and magnesium?
To react with excess magnesium to form magnesium chloride
Why can’t carbon be used in the reaction between titanium (IV) chloride and magnesium? What is another reducing agent that can be used?
Titanium will form a carbide so you can’t get pure metal Sodium
Why is titanium carbide not useful?
It is very brittle so not useful
Why is titanium extraction expensive?
Magnesium/sodium also have to be extracted from their ores before they can be used in the reaction
Why is group 2 called the alkaline earth metals?
Because their oxides and hydroxides are alkaline
What is the electronic configuration of group 2?
[Noble gas] s
What is the bonding present in the Alkaline Earth metals?
Metals with high melting points Giant metallic structure Going down the group, the delocalised sea of electrons is further away from the nucleus Therefore the metallic structure is weaker going down the bond Therefore the melting point decreases down the group Magnesium doesn’t follow this trend and has the lowest melting point
What are the rules for ionisation energy for group 2 elements?
They lose their two outer electrons to form +2 ions The amount of energy is equal to the sum of the first and second ionisation energies First and second ionisation energy decreases down the group as the distance and inner shielding increases
What is the rule of reactivity of group 2 elements?
The metals get more reactive going down the group
What is the trend in reactivity for the group 2 element’s reaction with water?
Reactivity increases down the group Magnesium reacts very slowly with cold water Calcium reacts vigorously even with cold water
What is a use of Mg(OH)2?
Milk of magnesia Used in indigestion to neutralise excess stomach acids