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Important Points of this chapter
  • Elements can be classified as metals and non-metals.
  • Metals are lustrous, malleable, ductile and are good conductors of heat and electricity. They are solids at room temperature, except mercury which is a liquid.
  • Metals can form positive ions by losing electrons to non-metals.
  • Metals combine with oxygen to form basic oxides. Aluminium oxide and zinc oxide show the properties of both basic as well as acidic oxides. These oxides are known as amphoteric oxides.
  • Different metals have different reactivities with water and dilute acids.
  • A list of common metals arranged in order of their decreasing reactivity is known as an activity series.

  • Metals above hydrogen in the Activity series can displace hydrogen from dilute acids.
  • A more reactive metal displaces a less reactive metal from its salt solution.
  • Metals occur in nature as free elements or in the form of their compounds.
  • The extraction of metals from their ores and then refining them for use is known as metallurgy.
  • An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.
  • The surface of some metals, such as iron, is corroded when they are exposed to moist air for a long period of time. This phenomenon is known as corrosion.
  • Non-metals have properties opposite to that of metals. They are neither malleable nor ductile. They are bad conductors of heat and electricity, except for graphite, which conducts electricity.
  • Non-metals form negatively charged ions by gaining electrons when reacting with metals.
  • Non-metals form oxides which are either acidic or neutral.
  • Non-metals do not displace hydrogen from dilute acids. They react with hydrogen to form hydrides.


Properties of some metals
  • The above activity shows that metals are good conductors of heat and have high melting points. The best conductors of heat are silver and copper. Lead and mercury are comparatively poor conductors of heat.
  • The metals that produce a sound on striking a hard surface are said to be sonorous
  • All metals except mercury exist as solids at room temperature.
  • Iodine is a non-metal but it is lustrous.
  • ( Carbon is a non-metal that can exist in different forms. Each form is called an allotrope.
  • Diamond, an allotrope of carbon, is the hardest natural substance known and has a very high melting and boiling point. Graphite, another allotrope of carbon, is a conductor of electricity.
  • Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. They have low densities and low melting points.
  • Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.
  • At ordinary temperature, the surfaces of metals such as magnesium, aluminium, zinc, lead, etc., are covered with a thin layer of oxide. The protective oxide layer prevents the metal from further oxidation.


  • Iron does not burn on heating but iron filings burn vigorously when sprinkled in the flame of the burner.
  • Copper does not burn, but the hot metal is coated with a black coloured layer of copper oxide.
  • Silver and gold do not react with oxygen even at high temperature
  • Anodising is a process of forming a thick oxide layer of aluminium. Aluminium develops a thin oxide layer when exposed to air. This aluminium oxide coat makes it resistant to further corrosion.

CORROSION

  • Silver articles become black after some time when exposed to air. This is because it reacts with sulphur in the air to form a coating of silver sulphide.

  • Copper reacts with moist carbon dioxide in the air and slowly loses its shiny brown surface and gains a green coat. This green substance is copper carbonate.

  • Iron when exposed to moist air for a long time acquires a coating of a brown flaky substance called rust.

Prevention of Corrosion
  • The rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys.


Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc. The galvanised article is protected against rusting even if the zinc coating is broken.



Alloying is a very good method of improving the properties of a metal. We can get the desired properties by this method.




Activity series and related metallurgy

Thus on the basis of reactivity, we can group the metals into the  following three categories – 
(i) Metals of low reactivity 
(ii) Metals of medium reactivity 
(iii) Metals of high reactivity.



The metals at the top of the activity series  (K, Na, Ca, Mg and Al) are so reactive that they are never found in  nature as free elements. The metals in the middle of the activity series  (Zn, Fe, Pb, etc.) are moderately reactive.


Aqua regia - is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of
3:1.
  • It can dissolve gold, even though neither of these acids can do so alone.
  • Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that is able to dissolve gold and platinum
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