Non-metals and metals

QUICK POINTS

Non-metals are usually electronegative, as they form ions by gaining electrons to form anions.

Non-metals are oxidising agents.

Non-metals react with air or oxygen to form oxides (acidic), which dissolve in water to form acids.

Non-metals do not react with water, steam or dilute acids. Non-metals form covalent compounds with other nonmetals, and ionic compounds with metals.

The reactivity of a non-metal depends on how close the outer shell is to the nucleus so that it can pull or attract electrons towards it. The most reactive non-metal is fluorine, as it has a strong attracting power towards electrons.

Carbon, oxygen and hydrogen are important non-metals present in all living systems. The processes of respiration and photosynthesis depend on oxygen and carbon dioxide.

Sulphur is used to produce sulphuric acid and is important in the making of proteins for the growth and development of tissues.

Nitrogen is also needed to make proteins. It is used to produce ammonia and nitric acid. Ammonium fertilisers are important in food production.

Group 7 elements are called halogens and have seven electrons in their outer shell. They ionise by gaining one electron to form a negative ion.

As non-metals, they react with metals for form salts and with water to form acids.

Reactivity of Group 7 elements increases up the work. They are oxidising agents, with fluorine having the most oxidising power.

QUESTION 1

The table gives information about the colours and physical states at room temperature of the halogens, chlorine, bromine and iodine.

(a) Complete the table.

Chlorine, bromine and iodine are in Group 7 of the periodic table. The order of reactivity of these three elements can be shown by carrying out displacement experiments.

You are provided with potassium bromide solution, potassium chloride solution, potassium iodide solution, bromine solution, chlorine solution, iodine solution.

(a) Describe how these solutions could be used to carry out experiments to show the order of reactivity of bromine, chlorine and iodine, explaining how the results would show the order of reactivity.

ANSWERS

(a) The completed table is shown:

(b) The order of reactivity of bromine, chlorine and iodine can be found by carrying out the following reactions.

(i) Chlorine solution and potassium bromide

(ii) Chlorine solution and potassium iodide

(iii) Bromine solution and potassium iodide

(iv) Bromine solution and potassium chloride

(v) Iodine solution and potassium chloride

(vi) Iodine solution and potassium bromide

When these solutions are mixed, if a reaction takes place, this will show that the halogen is more reactive to cause a displacement reaction, displacing the halide ion from solution. If no reaction takes place, this shows that the halogen is not more reactive and thus cannot displace the halide ion from solution.

Example: Cl 2 (aq) + KBr (aq) KCl (aq) + Br2 (aq). A redbrown colour would be seen.

This would suggest that chlorine is more reactive than bromine and displaces the bromide ion from the solution (KBr) to form aqueous bromine.

I 2 (aq) + 2KBr (aq) I2 (aq) + 2KBr (aq). No reaction.

This suggests that iodine is not more reactive than bromine and cannot displace the bromide ion from solution.

QUESTION 2

Metals are malleable.

(a) Explain, in terms of their structures, why metals are malleable.

Group 2 of the periodic table contains the alkaline earth metals berrylium, magnesium, calcium and strontium. These metals show a pattern in their reactivity with water when small pieces of magnesium, calcium and strontium are added separately to water.

(b) Describe the reactions and what would be seen, and explain the pattern in reactivity. You may include equations as part of your answer.

ANSWERS

(a) Metals are malleable because the metal atoms are arranged in layers (in a crystal lattice) that can slide past each other when hammered. This can lead to a change in shape, making metals malleable.

(b). The reactivity of the Group 2 metals with water can be determined by adding small pieces to water. Magnesium would show a vigorous reaction, with water forming magnesium hydroxide and giving off hydrogen gas. A similar reaction occurs for calcium and strontium.

Mg (s) + 2H O (l) Mg(OH)2 (aq) + H2 (g). Vigorous reaction. 2 Ca (s) + 2H O (l) Ca(OH)2 (aq) + H2 (g). Violent reaction. 2 Sr (s) + 2H O (l) Sr(OH)2 (aq) + H2 (g). Explosive reaction. 2

As you go down the group, the reactivity with water increases and becomes more explosive. So metals at the bottom of the group are more reactive than those at the top. Barium is the most reactive in Group 2, while berrylium is the least reactive.

Francine Taylor-Campbell is an independent contributor. Send feedback to kerry-ann.hepburn@gleanerjm.com.