Unit 2: Section 2 - Group 2 and Group 7 Elements

Question 1

What are the group 2 elements also known as?

Answer 1

The Alkaline Earth Metals

Question 2

How many valance electrons do group 2 elements have?

Answer 2

Two

Question 3

How many electrons do group 2 metals lose when they react?

Answer 3

Two

Question 4

What are the trends down group 2? (5)

Answer 4

Atomic radius increases
Level of shielding increases.
First ionisation energy decreases
Reactivity increases
Melting points decrease (generally)

Question 5

Explain the trend in the atomic radius of group 2 elements.

Answer 5

It increases as the level of shielding increases.

Question 6

Explain the trend in the first ionisation energy of group 2 elements.

Answer 6

It decreases as an increase in electron shells shield the valance electrons from the positive nuclear charge. The extra electron shells also mean the electrons are further away from the nucleus too. All these factors make it easier to remove the outermost electron.

Question 7

Explain the trend in the reactivity of group 2 elements.

Answer 7

It increases as elements are more reactive as ions and as you go down there is a decrease in first ionisation energy so ions are formed more readily.

Question 8

Explain the trend in the melting points of group 2 elements.

Answer 8

Group 2 elements have metallic structures. As you go down the group, the ions get bigger, but the number of delocalised electrons remains the same. The larger the atomic radius, the less the nuclear attraction they feel and therefore, the easier it is to break the metallic bonds. So the melting point decreases down the group. However, there is an exception with magnesium, which has a much lower melting point than it should due to its crystal structure changing.

Question 9

In the reaction between a group 2 element and water, which is the oxidising agent?

Answer 9

Water

Question 10

What happens to group 2 elements oxidation states when they react?

Answer 10

It goes from 0 to +2

Question 11

What is produced when a group 2 element reacts with water?

Answer 11

A metal hydroxide and hydrogen

Question 12

What are the trends in group 2 elements solubility down the group?

Answer 12

Sulfates decrease in solubility

Hydroxides increase in solubility

Question 13

What are the least soluble group 2 compounds?

Answer 13

Barium Sulfate and Magnesium Hydroxide

Question 14

What are the most soluble group 2 compounds?

Answer 14

Barium hydroxide and magnesium sulfate

Question 15

How are group 2 elements used to reduce acidity? (2)

Answer 15

Calcium hydroxide (slaked lime) is used in agriculture to neutralise acidic soil.
Magnesium hydroxide is used in some indigestion tablets as an antacid.

Question 16

What is the reaction that occurs between an acid and a group 2 compound?

Answer 16

H+(aq) + OH-(aq) –> H2O(l)

Question 17

Describe and explain a use of barium.

Answer 17

Barium sulfate is opaque to x-rays so it can be used to diagnose problems with the digestive system.
The patient swallows a barium meal, which moves through the digestive system and won’t be absorbed by the bloodstream because it’s insoluble.

Question 18

Describe and explain a use of magnesium. (include equation)

Answer 18

The extraction of titanium.
Titanium Oxide is converted to titanium chloride by heating it with carbon.
Titanium chloride is then purified by fractional distillation before being reduced by magnesium at 1000’C.

TiCl4(g) +2Mg(l) –> Ti(s) + 2MgCl2(l)

Question 19

Describe and explain a use of calcium. (include equations)

Answer 19

Burning fossil fuels produces sulphur dioxide.
The acidic sulphur dioxide can be removed from flue gases in a process called wet scrubbing.
A slurry is made by mixing calcium acid or calcium carbonate with water. The slurry is then sprayed onto the flue gases.

CaO(s) + 2H2O(l) + SO2(g) –> CaSO3(s) + 2H2O(l)

CaCO3(s) + H2O(l) + SO2(g) –> 2H2O(l) + CO2(g)

Question 20

What are the trends of group 7 elements down the group? (6)

Answer 20

Electronegativity decreases 
Boiling points increase 
Atomic radius increases
Shielding increases
Reactivity decreases
Relative oxidising ability decreases

Question 21

Explain the trend in the boiling points of the group 7 elements.

Answer 21

The size of the molecule and its relative mass increases, strengthening the van der Waals forces. This means more energy is required to break the bonds.

Question 22

Explain the trend in electronegativity of the group 7 elements.

Answer 22

Larger atoms attract electrons less than smaller ones do. This is because the electrons are further from the nucleus and more shielded. Therefore electronegativity decreases.

Question 23

Explain the trend in the reactivity of group 7 elements.

Answer 23

It decreases as the atoms become larger, so electrons are less attracted to the nucleus, therefore the valance electrons are more likely to leave.

Question 24

What is the basic rule of displacement for group 7 elements?

Answer 24

A halogen will displace a halide from the solution if the halide is below it in the periodic table.

Question 25

How is bleach made from chlorine? (inc. equation)

Answer 25

By mixing chlorine gas and cold, dilute sodium hydroxide.

2NaOH(aq) + Cl2(g) –> NaClO(aq) + NaCl(aq) + H20(l)

Question 26

What happens to the oxidation state of chlorine during the reaction that forms bleach? What does this mean?

Answer 26

The oxidation state of chlorine goes up and down (from 0 to 1 and -1). This means chlorine is both oxidised and reduced. When this happens it is called disproportionation.

Question 27

What is disproportionation?

Answer 27

When during a reaction a substance is simultaneously oxidised and reduced, giving two different products.

Question 28

What happens when chlorine gas reacts with water (in sunlight and in shade)?

Answer 28

In shade:
Cl2(g) + H2O(l) <==> 2H+(aq) + Cl-(aq) + ClO-(aq)

In sunlight:
2Cl2(g) + 2H2O(l) <==> 4H+(aq) + 4Cl-(aq) + O2(g)

Question 29

What are the benefits of treating water with chlorine? (3)

Answer 29

It produced chlorate ions which kill disease-causing microorganisms.
Some chlorine persists which prevents reinfection.
It prevents the growth of algae, eliminating bad smells and tastes and removes discolouration from organic compounds.

Question 30

What are the risks of using chlorine to treat water? (2)

Answer 30

Chlorine gas is very harmful if breathed in (it irritates the respiratory system) and liquid chlorine causes severe chemical burns.
Water contains a variety of organic compounds, which chlorine can react with to form chlorinated hydrocarbons and many of these are carcinogens.

Question 31

Explain the trend in the reducing power of halides as you go down the group.

Answer 31

It increases as the attraction of the valance electrons to the nucleus decreases due to a larger atomic radius and more shielding. This makes it easier for the halides to lose an electron.

Question 32

What happens when NaF or NaCl reacts with H2SO4? (inc. equations).

Answer 32

HF and HCl aren’t strong enough reducing agents to reduce the sulfuric acid so the reaction is not a redox reaction.

NaCl(s) + H2SO4(l) –> NaHSO4(s) + HCl(g)

Question 33

What happens when NaBr reacts with H2SO4 (inc. equations).

Answer 33

HBr is a stronger reducing agent than F and Cl so a redox reaction does occur.

NaBr(s) + H2SO4(l) –> NaHSO4(s) + HBr(g)
2HBr(aq) + H2SO4(l) –> Br2(g) + SO2(g) + 2H2O(l)

Question 34

What happens when NaI reacts with H2SO4 (inc. equations)

Answer 34

HI is a very strong reducing agent and keeps reducing.
Solid iodine (which looks grey or purple) is formed and so is H2S (which is toxic and smells like bad eggs).

NaI(s) + H2SO4(l) –> NaHSO4(s) + HI(g)
2HI(g) + H2SO4(l) –> I2(g) + SO2(g) + 2H2O(l)
6HI(g) + SO2(g) –> H2S(g) + 3I2(s) + 2H2O(l)