Metals are defined as those elements which possess lustre when freshly cut and are malleable and ductile and good conductor of heat and electricity.
Non-metals are defined as those elements which do not possess lustre and are neither good conductor of heat and electricity nor malleable and ductile but are brittle.
Importance of metals
Metals have a great importance in our everyday life. They are used for a large number of purposes. A few out of these are given below:
(i) Utensils used at home are made of aluminium, copper, brass, stainless steel, etc.
(ii) In the construction of buildings and bridges.
(iii) In the manufacture of automobiles, aeroplanes, ships, trains, etc.
(iv) In making of coins.
(v) Silver and gold are used in making of jewellery.
(vi) In making of almost all types of machine parts.
(vii) Some metals such as titanium (Ti), chromium (Cr), manganese (Mn), zirconium (Zr), etc, have a great significance as they are used in country’s defence. Hence, these metals are called strategic metals.
Importance of Non-metals
(i) Carbon is one of the most important non-metal because all the life on this earth is made of carbon compounds. Carbon, in form of graphite, is also used as electrodes in electrolytic cells and dry cells.
(ii) Another non-metal is hydrogen. It is present in almost all the compounds of carbon (i.e., carbohydrates, proteins, oils and fats etc.) which are required for growth and development of life. It is used in the hydrogenation of vegetable oil to make vegetable ghee.
(iii) Oxygen is another non-metal which is equally important for existence of life and combustion processes. It is present in air and is essential for breathing to maintain life. It is the most abundant element in the earth’s crust followed by silicon.
(iv) Nitrogen is an inert gaseous non-metal. Its presence in air reduces the rate of combustion.
(v) Another non-metal is sulphur. It is present in many of the substances found in plants and animals. Sulphur compounds are also present in proteins, hair, onion, garlic, wool etc.
Physical properties of metals and non-metals
Physical properties of Metals
1. Metals in the pure state possess lustre, i.e., a shining surface.
2. Metals are generally hard. The hardness varies from metal to metal.
3. Metals are generally malleable, i.e., they can be beaten into thin sheets.
4. Metals are generally ductile, i.e., they can be drawn into wires.
5. Metals are good conductor of heat and possess high melting points.
6. Metals are good conductor of electricity.
7. Metals are sonorous, i.e., they produce sound on striking hard surface.
8. Metals have high density.
9. The have high tensile strength.
10. All metals are solids (except mercury which is a liquid)
Physical properties of Non-metals
1. Non-metal do not possess any lustre.
2. They are soft and brittle.
3. They are neither malleable nor ductile.
4. They are generally bad conductors of heat and electricity.
5. They are non-sonorous.
6. They generally have low melting and boiling points.
7. They have low densities.
8. They have low tensile strength.
9. They may be solids, liquids or gases at room temperature.
Chemical properties of metals
Metals have low ionization energy. Ionization energy is the amount of energy required to remove the electrons from the valence shell (outermost shell) of an isolated gaseous atom so as to convert into a positive ion.
M(g) + Ionization energy → M+ (g) + e–
Hence, they are said to have electropositive character.
1. Reaction of metals with oxygen
Metal + Oxygen → Metal oxide
(a) Most of the metal oxides are insoluble in water.
(b) Most of the metal oxides are basic in nature.
2. Reaction of metals with water.
A number of metals react with water to form a hydroxide or an oxide along with the evolution of hydrogen gas.
(i) Sodium and potassium react even with cold water
2 Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2 (g)
Sodium Water Sodium hydroxide Hydrogen
2 K (s) + 2 H2O (l) → 2 KOH (aq) + H2(g)
Potassium Water Potassium hydroxide Hydrogen
(ii) Calcium also reacts with water at room temperature forming calcium hydroxide but the reaction is less violent. The heat evolved is not sufficient for hydrogen evolved to catch fire.
(iii) Lead, copper, silver and gold do not react even with steam.
K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au
3. Reaction of metals with dilute acids.
More reactive metals are those which react with dilute hydrochloric acid or dilute sulphuric acid and displace hydrogen of the acid forming salts. With hydrochloric acid, the salts formed are called metal chlorides whereas with sulphuric acid, the salts formed are called sulphates.
Less reactive metals are those which do not react with the above acids to produce hydrogen gas. These include copper, mercury and silver.
Comparison of physical and chemical properties of metals and non-metals
Comparison of physical properties of metals and non-metals
|1. Lustre||Metals have lustre and can also be polished.||Except iodine, non-metals do not have lustre and also cannot be polished.|
|2. Hardness||Metals (except sodium and potassium) are generally hard||Non-metals (except diamond and boron) are generally soft.|
|3. Malleability and ductility||Metals are malleable (can be hammered into thin sheets) and ductile (can be drawn into wires).||Non-metals are neither malleable nor ductile. They are actually brittle.|
|4. Conductivity||Metals are good conductors of heat and electricity.||Non-metals except graphite and gas carbon are bad conductors of heat and electricity.|
|5. Melting points and boiling points||Metals (except mercury and gallium) generally have high melting and boiling points.||Non-metals (except carbon and boron) have low melting and boiling points.|
|6. Sonorosity||Metals are sonorous (i.e., produce sound when hit with a hard object).||Non-metals are non-sonorous (i.e., do not produce sound when hit with a hard object).|
|7. Density||Metals generally have high density.||Non-metals generally have low densities.|
|8. Tensile strength||Metals generally have high tensile strength and hence cannot be easily broken.||Non-metals generally have low tensile strength and hence can be easily broken.|
|9. Physical state||Metals are generally solids (except mercury and gallium which are liquids) at room temperature.||Non-metals (except bromine which is a liquid) are either solids or gases at room temperature.|
Comparison of chemical properties of metals and non-metals
|1. Nature of ions||Metals are electropositive elements and hence lose one or more electrons to form positive ions.||Non-metals are electronegative elements and hence gain one or more electrons to form negative ions.|
|2. Nature of oxides||Metals form basic oxides.||Non-metals form either acidic or neutral oxides.|
|3. Reaction with dilute acids||Most of the metals displace hydrogen from water or stream.||Non-metals (except fluorine) generally do not react with water or steam.|
|4. Reaction with dilute acids||Metals which lie above hydrogen in the activity series displace hydrogen from dilute acids.||Non-metals do not react with dilute acids and hence do not displace hydrogen form dilute acids.|
|5. Nature of hydrides||Highly electropositive elements (i.e., K, Na, Ca etc.) react with hydrogen to form ionic hydrides which are generally unstable.||Non-metals form covalent hydrides which are quite stable.|
|6. Nature of chlorides||Metals generally combine with chlorine to form solid ionic chlorides which conduct electricity in the aqueous solution or in the molten state.||Non-metals combine with chlorine to form covalent chlorides. These are either gases or liquids. Since non-metal chlorides do not contain ions, therefore, they do not conduct electricity.|
|7. Oxidising and reducing behaviour||Metals have a strong tendency to lose electrons and hence they behave as reducing agents.||Non-metals have a strong tendency to accept electrons and hence they behave as oxidising agents.|
Electron dot representation (Lewis symbols)
G.N. Lewis introduced a simple method of representing the valence electrons by dots or small crosses around the symbol of the atom. These symbols are known as electron dot symbols or Lewis symbols.
Electron dot (Lewis symbols) of some common elements
|Element||Symbol||Atomic no.||Electronic ConfigurationK L M N||Valence electrons||Lewis symbol|
|Hydrogen||H||1||1||1||H* or Hx|
|Helium||He||2||2||2||He: or Hexx|
Properties of electrovalent (or ionic) compounds
1. Physical state: Most of the ionic compounds are crystalline solids. They are relatively hard because of strong electrostatic forces of attraction between the oppositely charged ions. They are brittle and break into pieces on applying force.
2. Solubility: They are soluble in water (which is a polar solvent) but insoluble in organic solvents like benzene, alcohol, ether, chloroform etc.
3. Melting points and boiling points: They have high melting and boiling points. This is because in the ionic compounds, the oppositely charged ions are held together by strong electrostatic forces of attraction. Hence, they require a lot of heat to cut off these forces of attraction and break them into ions.
Mineral and ores
The elementary state or the compounds in the form of which the metals occur in nature are calledminerals.
These earthy, sandy and rocky impurities associated with the mineral are called gangueormatrix.
The mineral form which the metal can be extracted conveniently and economically is called an ore.
The various steps involved in the extraction of the metal from its ores followed by refining of the metal is called metallurgy.
The three main steps involved in the extraction of any metal are:
(1) Enrichment of the ore or Concentration of the ore.
(2) Extraction of the metal from the concentrated ore.
(3) Refining of the impure metal.
Extraction of the Metal from the Concentrated Ore
The method used for the extraction of the metal from the concentrated one depends upon the nature of the metal. Based on their reactivity, the metals have been grouped into the following three categories:
(1) Metals of low reactivity (Low in the activity series).
(2) Metals of medium reactivity (In the middle of the activity series).
(3) Metals of high reactivity (At top of the activity series).
Refining of Impure Metals
The process of purifying the impure (crude) metal is called refining of the metal.
When an electric current is passed through the solution, the pure metal from the anode passes into the solution in the form of metal ions and an equivalent amount of metal ions from the solution are deposited as pure metal on the cathode.
At Anode: M(s) → Mn+(aq) + ne–
Metal atom (from anode) Metal ions
At Cathode: Mn+ (aq) + ne– → M(s)
Metal ions (from solution) Metal atom
The soluble impurities present in the impure metal pass into solution whereas insoluble impurities fall below the anode as anode mud or anode sludge. Thus, as the electrolysis proceeds, the size of the anode keeps on decreasing while that of the cathode keeps on growing.
What is corrosion?
The process or slowly eating up of metals due to their conversion into oxides, carbonates, sulphides, sulphates, etc. by the action of atmospheric gases and moisture is called corrosion.
Preventing of rusting
1. Painting: The most common method for preventing rusting of iron objects is to coat their surface with a paint. By doing so, air and moisture are not allowed to come in contact with the surface of iron objects and hence rusting does not take place. The window grills, railing, iron gates, steel furniture, iron bridges, railway coaches, bodies of cars, buses and trucks, etc. are all painted to protect them from rusting.
2. Greasing and oiling: When a thin film of grease or oil is applied to the surface of an iron object, the moisture and air cannot come in contact with it and hence rusting is prevented. For example, tools and machine parts made up of iron are covered with a thin film of grease or oil to prevent them from rusting.
3. Galvanization: The process of coating iron objects with a thin layer of zinc is called galvanization.
4. Coating with tin, chromium and nickel: These metals are resistant to corrosion. Thus, when a thin layer of these metals is deposited on the iron and steel objects by electroplating, they are protected from rusting.
5. Alloying with nickel and chromium: When iron is alloyed with chromium, nickel and some carbon [Fe = 74%, Cr = 18%, Ni = 8%], stainless steel is obtained. Stainless steel resists corrosion and hence does not rust.
An alloy may be defined as a homogeneous mixture of two or more metals, or a metal and a non-metal.
Objectives of alloy making
1. To increase hardness.
2. To increase tensile strength.
3. To increase resistance to corrosion.
4. To lower the melting point.
5. To modify chemical reactivity.
6. To reduce electrical conductivity.
7. To produce good casting.
8. To modify colour.
Q1. Difference between metals and non-metals.
Q2. Importance of non-metals.
Q3. What are Lewis symbols.