Metals and non-metals
Francine Taylor-Campbell, Contributor

In this lesson we will use our knowledge of the reactions of metals to answer some questions on the topic.

IMPORTANT POINTS

• Metals are elements which form ions by losing or giving up electrons.
• They form positive ions or cations.
• This makes them good reducing agents.
• The reactivity of a metal is based on how readily it will give up its valence electrons.
• The further away the outer electron is from the attractive pull of the nucleus, the more readily it will be lost.
• The reactivity series arranges metals in order of their reaction with oxygen, water and dilute acids. A more reactive metal will displace a less reactive metal from a solution of its salt.
• Metals exhibit the following physical properties: high melting and boiling points, good conductors of heat and electricity and generally solids which are malleable and ductile.

LET US NOW EXAMINE A FEW QUESTIONS.

1. (a) List three physical properties of metals. (3 marks)

(b) Sodium and rubidium (Rb) are metals in group one of the periodic table. Sodium is in period three and rubidium is in period five.

Write the molecular formula for the hydroxide, nitrate and carbonate of rubidium.

How would you expect the compounds in (b) (i) above to react when heated?

What method could be used to extract rubidium from its ore? Give one reason for your answer.

A small piece of rubidium was placed in distilled water. State two observations that you would expect to make. A piece of red litmus, placed in water at the end of the experiment, changed to blue. Explain this observation. (10 marks)

ANSWERS

1. (a)Three physical properties of metals are conductors of heat and electricity and high melting and boiling points.

(b) (i) Rubidium hydroxide - RbOH, Rubidium nitrate - RbNO3, Rubidium carbonate - Rb2CO3

Comment: Rubidium is in group one of the periodic table, along with sodium, Therefore, it has one electron in its outer shell and will form the +1 ion (Rb+1) like sodium. To form the compounds, just consider the charges on the ions and bring them together so that the charges cancel.

(ii) Based on the fact that rubidium will undergo similar reactions like sodium, we would expect the carbonate and hydroxide of rubidium to be stable, that is not decomposed by heat, while rubidium nitrate will decompose to form rubidium nitrite and oxygen.

2RbNO3 (s) ————— 2RbNO2 (s) + O2 (g)

heat

(iii) Rubidium could be extracted from its ore by the method of electrolysis.

Comment: Electrolysis is the method used to extract very reactive metals from their ores. Rubidium is more reactive than sodium, as it is below it in the group and will ionise and lose its electrons more readily.

(iv) Rubidium will dissolve rapidly in the water in a vigorous or explosive reaction. Effervescence will also be seen. The litmus changed from red to blue as an alkaline solution was now formed (RbOH).

Comment: Reactive metals react with water to form the hydroxide and to liberate hydrogen.

QUESTION 2

2. Calcium [40 Ca] and barium [137.36 Ba] are in the same group of the periodic table:

20 56

(a) State the number of electrons in the outer shell of the barium (Ba) atom. (1mark)

(b) Would you expect barium to be a metal or non-metal? (1 mark)

(c) Which of these elements would be more reactive? (1 mark)

(d) The mass number of barium is not a whole number. Explain how this is possible. (2marks)

(e) Write the formula for barium carbonate. (1 mark)

(f) (i) Write a balanced equation for the reaction between barium carbonate and dilute sulphuric acid. Suggest a reason why this reaction would be unsuitable for the laboratory preparation of carbon dioxide. (3 marks)

ANSWERS

2. (a) Barium has two electrons in its outer shell.

Comment: Calcium has two electrons in its outer shell (2:8:8:2) and since barium is in the same group, it will also have two outer electrons.

(b) Barium is expected to be a metal.

(c) Barium would be more reactive as it is below calcium in the group. Its outer electrons are further away from the nucleus and will be lost more readily.

Remember: the reactivity of a metal is based on how readily it gives up its outer electrons.

(d) An element generally has atoms of different masses or isotopes making it up. These isotopes occur in different relative proportions and when the contribution of each isotope is added up, the mass number may or may not be a whole number.

For example, neon consists of 90.92 per cent of neon-20, 0.26 per cent of neon-21 and 8.82 per cent of neon-22. When the atomic mass of neon is calculated, it is 20.2 (not a whole number).

(e) Barium carbonate - BaCO3 (Ba2+ ions and CO32 - ions).

(f) BaCO3 (s) + H2SO4 (aq) == BaSO4 (s) + CO2 (g) + H2O (l)

Comment: this reaction is unsuitable for preparing carbon dioxide because, as soon as the reaction starts, insoluble barium sulphate would be formed, which would hinder the progress of the reaction.

Japan's Makoto Kobayashi (left), and Toshihide Maskawa (centre), co-laureates of the Nobel Prize in physics, and Japan's Osamu Shimomura, co-laureate of the Nobel Prize in chemistry, pose for photographers with their medals during the Nobel Prize awards ceremony in Stockholm, Sweden, Wednesday, December 10. Amid royal pomp and circumstance, Sweden's King Carl XVI Gustaf handed out the prestigious 10 million kronor (US$1.2 million) awards in chemistry, physics, medicine, literature and economics at a ceremony in Stockholm.

Francine Taylor-Campbell is an independent contributor.