Group 2 Metals Flashcards
What are group two metals also known as?
The alkaline earth metals.
What bonding occurs in G2?
Metallic.
Starting from Be list G2 to Ra.
Be, Mg, Ca, Sr, Ba, Ra.
Trend of atomic radius down G2?
Increases.
Why does atomic radius change down G2?
More principal energy levels are occupied. These levels are further from the nucleus and additional shells shield the outer e-s from the nuclear charge. The outer e-s are attracted less strongly the further from the nucleus they are.
Trend of 1st ionisation energy down G2?
Decreases.
Why does the 1st ionisation energy change down G2?
Outer e- is removed more and more easily, e- is removed from a successively higher principal energy level further from the nucleus. More shielding/ no. of energy levels between the outer shell and the nucleus. Extra inner e-s shield the outer e-s from the increased nuclear charge so less energy is needed to remove it.
Trend of m.p and b.p down G2?
Decreases.
Why does m.p and b.p change down G2?
All metallically bond and each atom gives 2 e-s into the structure, the attraction between the + ion and - e-s hold the metal together, the stronger the attraction the higher the m.p. The + ions get bigger down the group and the extra shells of e-s shield the attraction of the metal ion nuclei and the free e-s. Metallic bonds get easier to break and m.p is lower.
What element is the exception to the m.p trend in G2?
Mg.
Why is Mg lower m.p?
Has a different metallic structure.
How does Mg react with water?
Reacts very slowly with cold water, readily with steam.
Equation for Mg and water?
Mg(s) + H2O(g) -> MgO(s) + H2(g).
How does Ca react with water?
Reacts with cold water.
Equation for Ca and water?
Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g).
How does Sr react with water?
Reacts quickly with water.
What is the equation for Sr and water?
Sr(s) + 2H2O(l) -> Sr(OH)2(aq) + H2(g).
How does Ba react with water?
Reacts very quickly with cold water.
Equation for Ba and water?
Ba(s) + 2H2O(l) -> Ba(OH)2(aq) + H2(g).
What is the trend in reactivity with water down G2?
Increase in reactivity.
Explain the trend in G2 reactivity with water.
Down the group the outer e-s are further from the nucleus and are lost more easily making the element more reactive. There is more shielding of the outer e-s as we go down the group.
Define solubility.
Dissolves in water.
Define insolubility.
Doesn’t dissolve in water.
As we go down the group how does reactivity of hydroxides change?
Increases.
As we go down the group how does reactivity of sulphates change?
Decreases.
How soluble is Mg(OH)2?
Sparingly.
What is magnesium hydroxide used for?
Laxatives, medicine for digestive upset.
What is calcium hydroxide used for?
In agriculture to neutralise acidic soil.
What is calcium oxide or calcium carbonate used for?
Remove sulphur dioxide from flue gases in a chimney. Line the chimney with it and it reacts with the sulphur dioxide. They are both bases, this is a neutralisation reaction.
How soluble is BaSO4?
Insoluble.
What is barium sulphate used for?
Barium meal is given to patients when X rays of the digestive system are needed. It can be used in medicine as it’s insoluble and isn’t absorbed.
What is magnesium used for?
Extract titanium from titanium chloride in industry to get titanium metal. Displacement reaction, Mg is more reactive than Ti.
Displacement equation for Mg and Ti?
2Mg + TiCl4 -> 2MgCl2 + Ti.
What do we do to test for sulphate ions?
Add 1cm^3 of dilute HCl to solution being tested. Add 1cm^3 of dilute barium chloride to test tube.
If sulphate ions are present what result occurs?
A white precipitate of barium sulphate is formed.
Why do we add acid to the solution in the sulphate test?
To remove any other ions that would also give a precipitate.
What other ions would give a precipitate if not removed by acid?
Carbonate ions, CO3^2-.
Why don’t we use sulphuric acid in our sulphate ions test?
It contains sulphate ions that would also give a white precipitate.
How do we calc. % mass?
Moles of one you know, mass of other reactant, difference in masses, do percentage over whole mass of reactants.
Write an ionic equation, with state symbols, to show the reaction of calcium with an excess of water.
Ca(s) + 2H2O(l) -> Ca2+(aq) + 2OH-(aq) + H2(g)
Write an equation for the thermal decomposition of zinc carbonate to zinc oxide.
ZnCO3 -> ZnO + CO2
How do you do % atom economy?
New comp/ old comp x 100
