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CBSE Class 10 Answered

What properties do we use while categorising elements as metals or non-metals?
Asked by agraharianiruddha | 15 Jun, 2018, 11:52: AM
answered-by-expert Expert Answer
While categorizing metals and non-metals we use their physical and chemical properties, such as 
 

Physical Properties of  Metals and Non-Metals:

 

 

Metals

Non-metals

Physical state

Metals are solids and heavy, except mercury and gallium which are liquid at room temperature.

Most of the non-metals are gases at room temperature. A few are solids such as sulphur and iodine. Bromine is the only non-metal which is liquid at room temperature.

Lustre

 

Metals in their pure state have a shining surface. This property is called metallic lustre. Metals can be polished to produce a highly reflective surface.

Non-metals do not have metallic lustre because most of them are in the gaseous state. However, silicon, iodine and graphite have a metallic lustre.

Hardness

 

Metals are generally hard, with the exception of sodium, potassium and lead which are soft and can be easily cut with a knife.

Non-metals which are solids are hard but brittle in nature. However, diamond which is an allotrope of carbon is the hardest naturally occurring substance.

Colour

 

Metals are grey or silver in colour, except copper which is reddish brown and gold which is yellow.

Non-metals occur in various colours. Iodine is purple, sulphur is yellow and chlorine gas is greenish yellow.

Malleability

 

Metals have the ability to withstand hammering and can be made into thin sheets. This property is called malleability.

Non-metals cannot be made into thin sheets by hammering, i.e. they are not malleable.

Ductility

 

The ability of metals to be drawn into thin wires is called ductility.

Gold and silver are the most ductile metals. It is observed that one gram of gold can be drawn into a wire with a length of 2 kilometres.

Non-metals cannot be drawn into wires, i.e. they are not ductile.

Thermal conductivity

Metals are good conductors of heat. Silver is the best conductor, followed by copper and aluminium. Because of this property, cooking vessels are made of copper and aluminium metals. Lead is a poor conductor of heat.

Non-metals do not conduct heat, except diamond and graphite, allotropes of carbon, are good conductors of heat.

Electrical conductivity

 

Metals are good conductors of electricity. The electrical conductivity of copper, aluminium and silver is comparatively high.

Non-metals are non-conductors of electricity. However, graphite, an isotope of carbon, is a good conductor of electricity.

Graphite is the only non-metal which is used in electrochemical cells because it is a good conductor of electricity.

Sonority

 

Metals produce a ringing sound when struck with a hard object. This property of metals is known as sonority, i.e. metals are sonorous.

This property is made use of for making wind chimes, metal bells etc.

Non-metals produce a dull sound when they are hit with some other material. Thus, they are non-sonorous.

The melting point and boiling point

 

Melting and boiling points of metals are very high. For example, the melting point of iron is 1539°C. However, mercury is a metal which is liquid at room temperature and sodium, gallium and tin have low melting points.

Non-metals have low melting and boiling points, except graphite which has high melting and boiling points.

Tensile strength

 

Metals can resist strain without breaking, i.e. they have high tensile strength.

Non-metals have low tensile strength. They are brittle and break easily on the application of strain.

Density

 

Density is a measure of mass per unit volume of a substance.

Most of the metals have high density, except sodium and potassium which have low density and float in water.

Non-metals have low density.

 

Chemical Properties of  Metals and Non-Metals:

 

 

Metals

Non-metals

Electronic configuration

Metals have 1, 2 or 3 valence electrons.

Non-metals usually have 4, 5, 6 or 7 valence electrons.

Valency

Metals are electropositive in nature because they readily lose electrons and form positively charged ions, i.e. cations.

Na   ̶  e   ̶    →   Na+

Valency: +1

 

Mg   ̶  2 e   ̶    →   Mg2+

Valency: +2

 

Al    ̶  3e   ̶    →   Al3+

Valency: +3

Non-metals are electronegative in nature because they readily gain electrons and form negatively charged ions, i.e. anions.

 

Cl  +   e   ̶    →    Cl   ̶

Valency: −1

 

O    +  2 e   ̶    →    Cl2   ̶

Valency: −2

 

N   +  3 e   ̶    →    Cl3   ̶

Valency: −3

Oxidising/Reducing nature

Metals lose electrons during a chemical reaction; they are good reducing agents.

Non-metals gain electrons during a chemical reaction; they are good oxidising agents.

Nature of oxides

Oxides of metals are basic in nature and dissolve in water to form alkaline solutions.

Oxides of non-metals are acidic in nature and dissolve in water to form acidic solutions.

Reaction with Acids

Metals does not usually react with H2. Metals placed above hydrogen in the activity series react with dil. HCl and dil. H2SO4 to liberate H2 gas.

M + 2HCl MCl2  +  H2

        (dil.)

M  +  H2SO4 MSO+  H2

           (dil.)

Non-metals does not react with dilute acids to liberate hydrogen.

 

Reaction with chlorine

Metals reacts readily with Cl2 to form chlo­rides.

 

Non-metals usually form chlorides, which are volatile covalent liquids or gases.

Reaction with water

On the basis of reactivity, metals react with water or steam to produce hydroxides or oxides.

No such reaction occurs with non-metals. [Exception: Cl2 dissolves in water to form chlorine water which contains hydrochloric acid.]

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