(General Science) CHEMISTRY - Metals, Non-Metals and Metalloids

GENERAL SCIENCE: CHEMISTRY


General Science Note for IAS Exam

Metals, Non-Metals and Metalloids

On the basis of their properties, elements can be categorized as metals, non-metals and metalloids.

Metals


An element that is malleable, ductile, and conducts electricity is called a metal. Gold, silver, iron, copper, tin lead and uranium are some examples of metals. Aluminum is the most abundant metal in the earth’s crust. Other major metals in the earth’s crust are iron, calcium, sodium, potassium and magnesium.

Important Properties of Metals


  • Metals are Malleable, i.e., they can be beaten into this sheets. Gold and silver are the most malleable metals. Next in the list are aluminum and copper. Silver foils are used for decorating sweets. Aluminum foils are used for packing chocolates, biscuits, medicines, cigarettes, etc. Aluminum and copper sheets are used to make utensils. Iron sheets are used to make a large variety of products, like boxes, buckets, tanks, etc.
  • Metals are ductile, i.e. the can be drawn into thin wires. Gold and silver exhibit highest ductility, followed by copper and aluminum. Copper and aluminum wires are used in electrical wiring.
  • Metals are good conductors of heat and electricity. Silver metal has been ranked as the best conductor of heat followed by copper and aluminum. That is why cooking utensils are usually made of copper or aluminum. Silver is the best conductor of electricity.
  • Metals are lustrous. Gold, silver and copper have a shining surface and can be polished. They are used for making jewellery and decoration pieces. On keeping air for a long time, metals lose their shine due to the formation of a layer of oxide sulphide or carbonate due to the action of various gases present in air.
  • Metals are hard except sodium and potassium, which are soft metals and can be cut with a knife.
  • Metals are solids at room temperature. Mercury is an exception. It is the only metal which is liquid at room temperature.
  • Metals generally have high melting and boiling points. Exceptions are sodium and potassium which have low melting points. Melting points of gallium and caesium are so low that they start melting in hand.

Non-Metals


An element which is neither malleable nor ductile and does not conduct electricity is a non- metals. Carbon, sulphur, hydrogen, oxygen chlorine, and iodine are some examples of non-metals. Diamond and graphite are also non-metals. They are the allotropic forms of carbon. Carbon is very important non-metal because carbon compounds like proteins, fats, carbohydrates, vitamins and enzymes, etc. are essential for the growth and development of living organisms. Oxygen is essential for breathing and combustion of fuels. Sulphur is present in hair, wool, onions and garlic. The major non-metals in the earth’s crust in the decreasing order of their abundance are oxygen silicon, phosphorus and sulphur.

Important Properties of Non-metals


  • Non-metals are brittle. They cannot be beaten into thin sheets or drawn into wires because of their brittleness.
  • Non-metals are bad conducts of heat and electricity, Many non-metals are insulators. There are a few exceptions. For examples, diamond is a good conductor of heat and graphic is a good conductor of electricity. Graphic is, therefore used for making electrodes in dry cells.
  • Non-metals are dull in appearance, i.e., they do not have luster. Iodine is an exception. It has a shining surface like that of metals.
  • Non-metals are quite soft. Carbon in the form of diamond is an exception. In fact, diamond is the hardest natural substance known.
  • Non-metals can exist as solids (e.g., carbon, sulphur and phosphorus), liquids (e.g., bromine) and gases (e.g., hydrogen, oxygen, nitrogen and chorine).
  • Non-metals have low melting and boiling points, except graphite which has very high melting point.
  • Non-metals have many different colours. Sulphur is yellow, phosphorus is white or red, graphite is black, chlorine is yellowish green, bromine is reddish-brown hydrogen and oxygen are colour less.

Metalloids


Element which show some properties of metals and non-metals, i.e., properties intermediate between those of metals and non metals, are called metalloids. For example, despite looking like metals, they are brittle like non-metals. Instead of being good conductors of electricity like metals or insulators like non-metals, they are semi-conductors. Boron, silicon and germanium are examples of metalloids.

Compounds


A compound is a substance that can be broken down into two or more elements in fixed proportions by mass. Properties of a compound are different from those of its component elements. For examples, water is a compound made up of two elements, hydrogen and oxygen.

Other examples of compounds: Common salt (sodium chloride), sand (silicon dioxide), marble (calcium carbonate), chalk (calcium carbonate), limestone (calcium carbonate), quick lime (calcium oxide), slaked lime (calcium hydroxide), baking soda (sodium bicarbonate), washing soda (sodium carbonate), methane, hydrochloride acid, sodium hydroxide, sugar, starch, etc,

Difference between Mixtures and Compounds


Mixture Compound

1.

A mixture can be separated into its components by physical methods, like filtration, distillation, etc.

A compound can be separated into its constituents only by chemical methods and not by physical methods.

2.

A mixture exhibits the properties of its components.

A compound shows properties which are entirely different from those of its components.

3.

No energy changes are involved in the formation of a mixture.

Energy is evolved or absorbed during formation of a compound.

4.

Composition of a mixture is variable.

Composition of compound is fixed.

5.

A mixture does not have a fixed melting/boiling point.

A Compound has a fixed melting/boiling point.



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