Chapter 3: Metals and Non-metals
Physical properties of metals and non-metals
Metals are lustrous, hard (except Na and K), malleable (can be beaten into sheets), ductile (can be drawn into wires), good conductors of heat and electricity, have high melting points and are sonorous. Mercury is a liquid. Non-metals are usually brittle, dull and poor conductors. Exceptions: graphite conducts electricity, diamond is the hardest substance and iodine is lustrous.
Chemical properties and the reactivity series
Metal + oxygen â metal oxide (usually basic). Al2O3 and ZnO are amphoteric. Oxides of non-metals are usually acidic. Sodium and potassium are very reactive, so they are kept in kerosene oil.
A metal higher in the series is more reactive and can displace a metal below it from its compound.
Ionic compounds
A metal gives electrons and a non-metal takes them, forming ions (like NaCl). They are hard, brittle solids with high melting points. They do not conduct electricity as solids, but they do in the molten state or in solution, because the ions are then free to move.
Metallurgy and prevention of corrosion
Low reactivity (Hg, Cu): extracted by heating alone. Medium reactivity (Zn, Fe, Pb): ore is converted to oxide and reduced with carbon. High reactivity (Na, Mg, Al): electrolysis of the molten compound. Prevention of rusting: painting, oiling, galvanisation and making alloys.
Important questions
Q1. Name one metal and one non-metal that are liquid at room temperature.
Metal: mercury. Non-metal: bromine.
Q2. Why are sodium and potassium kept in kerosene oil?
They react so vigorously with oxygen and moisture in air that they can catch fire. In oil they are protected from air.
Q3. Which are the most malleable and ductile metals?
Gold and silver.
Q4. Name a non-metal that is lustrous.
Iodine.
Q5. Name a non-metal that conducts electricity.
Graphite (a form of carbon).
Q6. What do metals form when they react with oxygen?
Metal oxides, which are usually basic. For example, 2Cu + O2 â 2CuO.
Q7. What are amphoteric oxides? Give examples.
Oxides that react with both acids and bases, such as Al2O3 and ZnO.
Q8. What is the reactivity series?
Metals arranged in decreasing order of reactivity: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
Q9. Which metals react with cold water?
Sodium, potassium and calcium. The reaction of sodium and potassium is very vigorous.
Q10. What is formed when zinc reacts with dilute HCl?
Zinc chloride and hydrogen gas: Zn + 2HCl â ZnCl2 + H2.
Q11. Give an example of a displacement reaction between metals.
Fe + CuSO4 â FeSO4 + Cu. Iron is more reactive than copper, so it displaces copper.
Q12. What are ionic compounds?
Compounds formed by the transfer of electrons from a metal to a non-metal, such as NaCl.
Q13. State two properties of ionic compounds.
They are hard, brittle solids with high melting and boiling points, and they dissolve in water.
Q14. Why do ionic compounds not conduct electricity in the solid state but conduct in the molten state?
In the solid, the ions are fixed in place. In the molten state or in solution the ions are free to move, so current can flow.
Q15. What is an ore?
A mineral from which a metal can be extracted profitably.
Q16. What is gangue?
The impurities such as soil and sand that are mixed with an ore.
Q17. How is a metal of medium reactivity, such as zinc, extracted?
The ore is first converted into an oxide by roasting (sulphide ores) or calcination (carbonate ores), and then reduced with carbon: ZnO + C â Zn + CO.
Q18. How is sodium metal extracted?
By electrolysis of molten NaCl. Sodium is deposited at the cathode.
Q19. What is galvanisation?
Coating iron or steel with a layer of zinc. Even if the layer is scratched, zinc, being more reactive, still protects the iron from rusting.
Q20. What is an alloy? Give an example.
A homogeneous mixture of two or more metals (or a metal and a non-metal). For example, brass (copper + zinc) and stainless steel.
Quiz
1. Which metal is liquid at room temperature?
Mercury is the metal that is liquid at room temperature.
2. Which metal is the best conductor of electricity?
Silver is the best conductor, followed by copper.
3. What is coating iron with a layer of zinc called?
It protects iron from rusting.
4. What are oxides of non-metals usually like?
Oxides of non-metals are usually acidic.
5. By which method is sodium extracted?
Highly reactive metals are extracted by electrolysis.