Metals and Non-Metals for Class 10th
Some Important Notes
Introduction
In our day to day life we use many well-known materials like iron, aluminum, copper, gold, silver and many more. We are also familiar with the elements like oxygen, carbon, Sulphur as well. These are all obtained from some naturally occurring substances encompassing one or more elements or their compounds. They are termed as minerals. Minerals form which elements can be profitably extracted are termed as ores.
There 92 well known naturally occurring minerals of which 70 are metals and rets 20 are the non-metals.
Some metals possess the characteristics of both metals as well as non-metals. They are termed as metalloids. For instance, boron, silicon, germanium, arsenic, antimony, tellurium, and polonium.
Elements found in free state includes some metals like gold, silver, platinum etc. and some non-metals like helium, neon, argon etc. as well.
A major proportion of metals are found in combined states like oxides, sulphides, carbonates, silicates etc. Some non-metals like sulphur, phosphorous too are found to exist in combined state.
Physical properties of metal
Metals are solid except mercury that is found in liquid state at room temperature.
They are hard and tough except sodium and potassium that can be cut with a knife.
They are lustrous i.e. they shine in light because metals possess free electrons that vibrates on getting in contact with light.
They have high melting points except caesium and gallium have very low melting point.
They are good conductors of heat and electricity. The best conductors of electricity are silver and copper whereas lead and mercury are comparatively poor conductors.
They have high density except alkali metals like lithium, sodium and potassium.
They are malleablee. they can be beaten into thin sheets. For instance, the aluminium foil we use to pack food is manufactured by beating the aluminium metal into thin sheets. This a characteristic property of metal.
They are ductile. they can be drawn into wires. For instance. We all are familiar with copper and aluminium wires. It is due to their characteristic property of ductility that these metals can be drawn into wires.
They are sonorouse. they produce a ringing sound when struck against a hard object. For instance, your school bells are made of metal that produces a ringing sound after the period is over when struck hard by a hammer.
Examples are iron, gold, silver, magnesium, copper, aluminium and many more.
Physical properties of non-metals
Non-metals may be either solids, liquids or gases.
Solid non-metals are brittle and break down into powdery mass on striking with a hammer except diamond which is the hardest non-metal.
They have a dull luster but iodine is lustorous.
They have low melting points except diamond that has very high melting point.
They are poor conductors of heat and electricity except graphite.
They are not malleable.
They are not ductile.
They are not sonorous.
Examples are carbon, Sulphur, oxygen, phosphorous and many more.
Reactions of metal with oxygen
Metals reacting with oxygen is observed in our day to day life. We all must have observed rusting of iron, silver jewellery getting tarnished, or copper articles getting covered by green layer. Metals reacts with atmospheric oxygen and produces metal oxides that are basic in nature because they react with water to form bases.
In case of rusting of iron, the iron reacts with the oxygen present in air and moisture and develops rust (hydrated iron (III) oxide).
In case of rusting of copper, the metallic copper reacts with oxygen, carbon-dioxide and atmospheric moisture and develops a green coloured coating of copper hydroxide and copper carbonate.
In case of tarnishing of silver articles, the metallic silver reacts with hydrogen sulphide or sulphur present in air and gets tarnished.
Copper burns in air to combines with oxygen and form copper (II) oxide, a black oxide.
Exceptions to metallic oxides being basic in nature
Aluminium forms aluminium oxide.
And show both acidic as well as basic actions. Such metal oxides reacting with both acids as well as bases to produce salts and water are known as amphoteric oxides.
Metallic oxides are generally insoluble in water but some of the metallic oxides like Sodium oxide and potassium oxide dissolves in water to produce alkalis.
At normal temperature, the surfaces of metals such as magnesium, aluminium, zinc, lead, etc., develops a coating of thin layer of oxide. The protective oxide layer prevents the metal from further oxidation.
Magnesium burns in air to form magnesium oxide.
2Mg + O2 --> 2MgO
Iron does not burn on heating but iron filings burn vigorously when scattered
in flames.
Copper does not burn on heating , but the hot metal develops a coating of black coloured copper(II) oxide.
2Cu + O2 ---> 2CuO
Silver and gold do not react with oxygen even at high temperatures.
Reactions of metal with water
Sodium being very reactive reacts vigorously with water leading to the production of sodium hydroxide and hydrogen. Therefore it is stored in kerosene.
2Na + 2H2O à 2NaOH + H2
Magnesium does not react with cold water. Magnesium undergoes reaction with hot water to form magnesium hydroxide and hydrogen.
Mg +H2O à Mg(OH)2 + H2
The reaction of calcium with water evolves heat that is not sufficient for the hydrogen to catch fire.
Ca (s) + 2H2O(l) à Ca(OH)2 (aq) + H2 (g)
Whereas metals like aluminium, iron and zinc reacts neither with cold nor
hot water. Instead they react with steam to form the metal oxide and hydrogen.
Metals including lead, copper, silver and gold do not react with water at all.
Reactions of metal with acids
Metals react with acids to produce hydrogen gas. If a matchstick is brought near the mouth of the tube containing the product of the reaction then we hear a pop sound. It is this hydrogen gas that burns with a pop sound.
For instance, Magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen.
Mg + 2HCl --> MgCl2 + H2
Copper does not react with hydrochloric acid but reacts with sulphuric acid.
CuO + H2SO4 --> CuSO4 + H2O
Hydrogen gas is not evolved when a metal reacts with nitric acid. This is due to the fact that HNO3 is a strong oxidising agent. It oxidises the H2 produced to water and gets reduced to any of the nitrogen oxides (N2O, NO, NO2). But magnesium (Mg) and manganese (Mn) react with very dilute HNO3 to evolve H2 gas.
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