Physical properties of metals
Metal and Non-metals of Class 8
All metals (except mercury and gallium) are solids at room temperature. Mercury, gallium (at 300C), caesium and francium occur in liquid state in nature.
Liquid Metal : Mercury
METALS ARE MALLEABLE:
Metals are generally malleable. This means that the metals can be beaten with a hammer into very thin sheets without breaking. This property of metals is called malleability. Gold and silver are among the best malleable metals. Aluminium and copper are also highly malleable metals. All metals are not malleable. e.g. sodium, potassium & calcium are not malleable.
Sodium can be easily cut with a knife
METALS ARE DUCTILE:
It means that metals can be drawn (stretched) into thin wires. This property of metals is called ductility. Gold and silver are the most ductile metals. Copper, aluminium and tungsten are also very ductile, and therefore, these can be drawn into thin wires which are used in electrical wiring. Metals like Na, K, Ca etc. are not ductile, while metals like Sn. Pb etc. are less ductile.
METALS ARE GOOD CONDUCTORS OF HEAT AND ELECTRICITY:
All metals are good conductors of heat and electricity. The ability of metals due to which they allow electric current and heat to pass through them is called electrical and thermal conductivity respectively. Silver is the best conductor of heat. Copper and aluminium are also good conductors of heat and therefore, they are used for making household utensils. Lead is the poorest conductor of heat. Mercury metal is also a poor conductor of heat.
The electrical and thermal conductivities of metals are due to the presence of free electrons in them. Among all the metals, silver is the best conductor of electricity. Copper and aluminium are the next best conductors of electricity. Since silver is expensive, therefore, copper and aluminium are commonly used for making electric wires.
METALS ARE LUSTROUS AND CAN BE POLISHED :
Most of the metals have metallic lustre (shine) and they can be polished. The shining appearance of metals is also known as metallic lustre. For example, gold, silver and copper metals have metallic lustre.
METALS HAVE HIGH DENSITIES:
Most of the metals are heavy and have high densities. For example, the density of mercury metal is very high (13.6 g cm-3). However, there are some exception. Sodium, potassium, magnesium and aluminium have low densities. Densities of metals are generally proportional to their atomic masses.
The smaller the metal atom, the lesser is its density. OSMIUM has maximum density (22 g cm-3) among all elements.
METALS ARE HARD:
Most of the metals are hard, but all metals are not equally hard.Metals like iron, copper, aluminium etc. are quite hard. They cannot be cut with a knife. Sodium and potassium are common exceptions which are soft and can be easily cut with a knife.
METALS HAVE HIGH MELTING AND BOILING POINTS:
Most of the metals (except sodium and potassium) have high melting and boiling points.
METALS ARE RIGID: Most of the metals are rigid and they have high tensile strength.
METALS ARE SONOROUS: Most of the metals are sonorous i.e., they make sound when hit with an object.
COLOUR: Most metals are white or silvery-grey in colour. Exceptionally, gold is yellow (yellow metal) and copper is reddish-brown.
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