INTRODUCTION
There are 118 different elements known to us today. These elements are widely distributed in earth's crust in free state as well as in the combined form.
Approximate relative abundance of some elements in the earth crust are :
Oxygen-46.6%
Aluminium-8%
Calcium-3.6%
Potassium-2.8%
Hydrogen-0.14%
Silicon-27.7%
Iron-5%
Sodium-2.8%
Magnesium-2.1%
Phosphorus-0.12%
These elements have been classified into metals and non-metals based on their properties. Of these known elements, only 17 are non-metals.
METALS
Metals are those elements which can be drawn into sheets or pulled into wires, have high densities, high melting and boiling points and high tensile strength and are good conductors of heat and electricity.
The knowledge of metals is very old. Copper was the first metal to be used by man for making utensils, weapons and for other purposes.
Gold, silver, copper, lead, iron, tin, antimony and mercury (earlier named quick silver) have been known to mankind from the ancient times.
Metals are widely used in our daily life for a large number of purposes. Some of the metals are used in making jewellery and coins; some are employed making utensils and furniture, and some in the construction of heavy machinery, tools, transport vehicles and many in the manufacturing of other equipments. Metals often find applications as catalysts in various industrial processes such as hydrogenation of vegetable oils, manufacture of ammonia, sulphuric acid, nitric acid, dyes, drugs, etc. Metals, though in small quantities, have also been recognized as essentials for various biological processes. For example, iron is a constituent of blood pigment (haemoglobin) and zinc is present in insulin, cobalt is present in vitamin B-12, magnesium is present in chorophyll (plant pigment).
Metals are defined as the elements which form positive ions by the loss of electrons. Hydrogen is a non-metal which also forms positive ions.
Physical Properties of Metal
- All metals are solid at room temp. (except mercury & gallium)
- They are good conductors of electricity & heat generally insoluble in water & other solvent.
- They are generally hard.
- They have high density. (except alkali metals).
- They have high melting to boiling point.
NON-METALS
Non-metals are small in numbers but they play a very vital role in our daily life.
Non-metals, except hydrogen, are the elements which form negative ions by the gain of electrons.
Hydrogen, the lightest element known, is used in the hydrogenation of vegetable oils to make ghee. as a fuel and in the manufacture of compounds. It is also the essential part of organic compounds. Proteins, fats, carbohydrates, enzymes, vitamins, etc., are all compounds of carbon, and are essential for the growth and development of living organisms. The presence of oxygen gas in air is essential for respiration, and for combustion. Nitrogen is the most abundant element present in the atmosphere. Its presence in air reduces the rate of combustion. Due to its inertness, it is also used to preserve food. Life would not have been possible in the absence of non metals like carbon, oxygen, nitrogen and hydrogen.
- All the metallic elements (except mercury) are solids.
- 11 non-metals are gases, one is a liquid (bromine) and the remaining non metals are solids. Astatine is at the bottom of halogen group, but no one knows what it looks like. It is the rarest naturally occuring element.
- Certain elements which show properties of both metals and non-metals are called metalloids or semi-metals. They are: Boron (B), Silicon (Si). Germamun (Ge), Arsenic (As). Antimony (Sb), Telluriam (Te) and Polonium (Po).
In periodic table, the metals have been placed on the left side and in the middle, whereas non metals have been placed on the right side. Elements in Group 13 (except Boron) are metals and their metallic nature increases on moving down the group. Elements of Group 14, 15, 16 and 17 are mostly non-metallic, though a few elements at the bottom of the group show some metallic nature. Only one non-metal, i.e., hydrogen [H] has been placed on the left side of the Periodic Table.
The metals and non-metals in the Periodic Table are separated by a zig-zag line of metalloids.
Physical Properties of Non-Metal
- Non-metals at gases, liquids temperature or brittle solids at room temp.
- They are bad conductors of heat electricity.
- They have low melting & boiling points..
- They are generally soft(diamond).
- They have love density.
OCCURRENCE OF METALS
The earth's crust is the biggest source of metals. Metals can either occur in their native (free) state or in a combined state.
Occurrence of metals can be explained on the basis of activity series.
Metals which are less reactive and do not react under normal conditions with oxygen, water, carbon dioxide and other common reagents, occur in native state. Gold and platinum are less reactive metals so they occur in native state (free state).
Most of the metals are reactive so they occur in combined state in the form of their oxides, carbonates, halides, sulphides, sulphates, etc. mixed with mud, clay, sand and stone.
For example, sodium and potassium occur mainly as their chlorides, calcium and magnesium as carbonates, aluminium as its oxide while zinc, lead, copper, mercury and silver are found as sulphides.
Since the reactivity series lists the metals in the decreasing order of electropositivity, it might be expected that those at the top would combine with more electronegative elements in their minerals.
MINERALS AND ORES
Minerals are the naturally occuring compounds of metals which are generally mixed with other substances such as soil, mud, sand, silica (SiO₂) limestone, rocks, etc. These earthly impurities are called gangue or matrix.
Ores are those minerals from which metals are extracted commercially at a comparatively lower cost and with minimum effort.
All minerals are not ores, but all ores are minerals.
Reactivity Series
Note: Insoluble ores are found as rocks while soluble ones like alkali chloride are washed away by the rains and are found in sea water.
Common Ores Of Aluminium, Iron And Zinc
Aluminium:- Main ore of is bauxite(Al2O3.2H2O) from which it is extracted.
Iron:- Iron is mainly extracted from its chief ore haematite (Fe2O3).
Zinc:- Main ore of zinc is zinc blende (ZnS) from which zinc is extracted.
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