Class 7 Science Metals and Nonmetals Chapter Notes

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Metals and Nonmetals
All the elements found on the earth can be divided into metals and nonmetals. Metals generally have one or two or three electrons in their outermost shell. Metal atoms therefore lose one or two or three electrons and become positively charged ions called cations. Non-metals have four or more valence electrons and so they gain one or more electrons and form negatively charged ions called as anions.

Elements can be classified into metals and non-metals on the basis of their properties:

Physical Properties include
* Appearance
* Density
*Melting and boiling point
* Conductivity of heat and electricity
*Tensile strength
* Malleability (ability to be beaten into thin sheets by hammering)
* Ductility (ability to draw into thin wires)

Chemical Properties include
* Charge on ions formed from elements
* Types of bonding and properties of oxides

Metals are
*Lustrous or give shining
* Have moderate to high density
* Generally solid with exception of mercury being liquid at room temperature.
* Have generally moderate to high melting point.
* Generally good conductors of heat and electricity.
*High tensile strength.
*Malleable and ductile.
* Forms positive ions and generally form ionic compounds.
* Oxides of metal are basic with exception of zinc and aluminium which forms amphoteric oxides.

Non Metals
* Are dull in appearance
* Density is low to moderate
*Can exist in solid, liquid and gaseous state (liquid non-metal is Bromine)
* Have wide range of melting and boiling point.

* Generally are bad conductors of heat and electricity exception is graphite which is good conductor.
* They are generally brittle exception being diamond.
* Non-malleable and non-ductile
* Generally forms negative ions
* Bonding is covalent
*Oxides are generally acidic in nature.

Metals are placed on the left side of periodic table where as non-metals are placed on right side of periodic table.
*There are elements which have both metallic and non-metallic properties called as metalloids. e.g. Si, Ge, As, Sb, etc.
* Metals like gold and silver are called as noble metals because they are found in native states and are least reactive.
* Non-metals like alc. He, Ne, Ar, Kr, Xe and Rn are called inert gases or noble gases because they are unreactive elements.

Some common ores of metals Ores are those minerals from which metals are extracted profitably and with highest purity through processes of metallurgy are called Ores.

USES OF METALS

a) Iron: It is used in making pipes, tanks, cylinders, agricultural tools, nail, etc. Steel is used to make bridges, ships, buildings, utensils and machine parts. Steel is formed by mixing iron with carbon while stainless steel have Fe, C, Ni and Gr.

b) Copper: It is a good conductor of heat and electricity. It is used in making electric wires, cables and utensils.

c) Aluminium: It is light, strong and has high tensile strength. It is used to make bodies of aircraft, automobiles, machine tools and parts.

d) Zinc: Zinc does not rust easily and is used to coat iron sheets by a process known as galvanization.

e) Mercury: Property of not wetting glass and expanding a lot when heated make a mercury ideal for being used in thermometers.

f) Silver: The lustre of this metal has made it popular for making jewellary. Things made of other metals are often coated with a protective layer of silver called electroplating.

g) Gold: Gold is used for making jewellary, plating metals and in medicines. The purity of gold is measured in carats. Pure gold is 24 carat.

USE OF NON-METALS

a) Carbon: Both graphite and diamond are allotropic forms of carbon. Graphite is used to make lead of pencil and crucibles. Diamond is used to make tools for cutting and grinding glass and rocks. It is also used in jewellary.

b) Sulphur: Sulphur is used in the manufacture of sulphuric acid, gunpowder, dyes, matches and fireworks. It is also used to treat rubber in a process called as vulcanisation.

c) Phosphorus: Match-heads and fertilizers contain phosphorus.

d) Hydrogen: It is used to manufacture ammonia and hydrogen chloride. Vegetable oil is treated with hydrogen, it becomes solid like butter. This process is known as hydrogenation of vegetable oils.

e) Silicon (Metalloid): It is a semiconductor. It is used to make water proof materials, polishes and as an insulator in the electrical appliances.

Alloys: Alloys are homogenous mixtures of two or more metals. Some of them may contain traces of nonmetals also

a) Brass: It contains 60% copper and 40% zinc. It is used to make electronic equipment parts of telescopes and microscopes.

b) Bronze : It contains 80% copper 10% Zn and 10% tin. It is used to make statues, coins, bells and parts of some machines.

c) Solder: This alloy is made of lead and tin. It is used for joining electric wires.

d) Stainless steel : It consists of iron, carbon, chromium and nickel. It is used to make ships, bridges, railway lines, machinery, buildings, etc.

e) Duralumin: It consists of aluminium, copper, magnesium and manganese. It is used to make bodies of aeroplanes, automobiles, spacecraft, ships and pressure cookers.

Corrosion of metals
The slow destruction of material by chemical reaction is called as corrosion.

Preventing corrosion

1. Use paint or grease to prevent the contact with air,

2. Coating with another metal like Zn

3. Alloying.