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Class 8 Science Metals and Non Metals Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.
Covers the following topics:
1.Metals and Nonmetals
2.Characteristics of Metals
3.Chemical Properties of Metals
4.Characteristic of Non Metals
5.Chemical properties of Nonmetals
6.Uses of Some Common Nonmetals
7.Oxides of Metals and Nonmetals
Metals And NonMetals
Lavoiser classified all elements into metals, nonmetals and metalloids on the basis of their properties. Some commonly used metals, nonmetals and metalloids are given below.
Metals : Iron, Copper, Gold, Silver, Aluminium, Zinc Lead are some commonly used meats.
Nonmetals : Hydrogen, Oxygen, Nitrogen, Carbon, Sulphur, Phosphorus, Chlorine, Bromine, Iodine are commonly used nonmetals.
Metalloids : Boron, Silicon, Arsenic and Germanium are some metalloids.
Characteristic Of Metal
•Some important characteristics of metals are :
•Metals are good conductors of heat and electricity.
•All metals except mercury are solid at room temperature. Mercury is the only metal which is liquid at room temperature.
•Metals are malleable and ductile – that is metals can be beaten into thin leaves and drawn into thin wires.Metals have lustre and can be polished.Metals have tensile strength.
•Metals are electropositive elements. That is, metals have a tendency to lose electrons and form positively charged ions, (called cations).
Occurrence of Metals
Metals occur in nature in the free as well as in the combined states.
•All metals which are not affected by water and by the gases present in the air occur in free state in nature.
•The naturally-occurring compounds of metals mixed with earthly materials are called minerals.
♦ A mineral from which a metal can be extracted on the commercial scale, economically and easily, is called an ore.
◊ Physical Properties of MetalsAll
metals show similar physical properties. There are however a few exceptions.
♦ Physical State : Under normal pressure, all metals except mercury are solids at room temperature. Mercury is liquid at room temperature.
♦ Colour : Most metals except gold and copper are silver-grey in colour. Copper is reddish-brown and gold is golden yellow.
♦ Appearance : All metals are shiny. The characteristic shine of metals is called metallic lustre. Thus all metals have metallic lustre. Metals can be easily polished.
♦ Hardness : Most metals are hard except sodium and potassium. Sodium and potassium metals can be easily cut with a knife. Osmium is hard enough to scratch glass.
♦ Tensile strength : Metals have high tensile strength. Metals are very strong. For example, iron can bear a lot of stress. That is why it is widely used in construction of buildings, bridges, railway lines etc.
♦ Malleability : Metals are malleable. This means that metals can be hammered into very thin sheets. Silver can be beaten to very thin leaves. You must have seen silver varak on burfee. Aluminium foil is
used in the packaging of food materials.
♦ Ductility : Metals are ductile. This means that metals can be drawn into thin wires. Silver and gold can be drawn into very thin wires.
♦ Conductivity : Metals are good conductor of heat and electricity. Silver is the best conductor of electricity. Copper is the next best conductor of electricity.
♦ Density : Metals, except sodium and potassium have high densities. Sodium and potassium have much lower densities.
♦ Sound : Metals are sonorous. Metals when hit by a hammer produce a ringing sound. That is why metal are used for making bells and wires for musical instruments.
◊ CHEMICAL PROPERTIES OF METALS
All metals give similar chemical reactions. However, the reactivity of a metal depends upon its nature and reaction conditions. Some typical reactions of metals are described below :
♦ Reaction with oxygen : All metals combine with oxygen to form metal oxides. Different metals react with oxygen under different conditions.
From the reaction conditions of the reactions given above, the order of reactivity of metals with oxygen is,
Sodium (Na) > Magnesium (Mg) > Zinc (Zn) > Iron (Fe) > Copper (Cu)
♦ Reaction with Water : Different metals react with water under different conditions. Reactions of some common metals with water are given below :
♦ Reactions with Acids : Most metals react with dilute acids produce salt and hydrogen gas. Reaction of some common metals with dilute hydrochloric acid are given below :
From the reaction conditions of the reaction given above, the order of reactivity of these metals with dilute acid is
Sodium (Na) > Magnesium
(Mg) > Zinc (Zn) > Iron (Fe) > Copper (Cu)
♦ USES OF SOME COMMON METALS
Main uses of some common metals are listed below :
♦ CHARACTERISTICS OF NON-METAL
Some important characteristics of metals are :
♦ Nonmetals are soft solids, liquids or gases.
♦ Nonmetals (except graphite) are nonconductors of heat and electricity.
♦ Solid nonmetals are brittle.
♦ Nonmetals (except graphite and diamond) are low melting and low boiling.
♦ Nonmetals are electronegative elements. That is, nonmetals have a tendency to gain electrons and form negatively charged ions (called anions).
◊ Occurrence of Nonmetals
Many nonmetals occur free in nature, whereas metal many more occur only in the form on their compounds as minerals.
The modes of occurrence of some typical nonmetal are described below :
Most nonmetals are either mined directly from their mines or obtained as by-products in some industrial processes.
♦ Nitrogen and Oxygen are obtained from the air by fractional distillation of liquid air.
♦ Chlorine is obtained from common salt by electrolytic method.
♦ Sulphur is mined in its elemental form
♦ Nonmetals such as phosphorus and silica are obtained from their ores by chemical methods.
◊Physical Properties of Nonmetals
Some common general physical properties of nonmetals are given below :
♦ Physical state : Nonmetals may occur as solids, liquids or gases at room temperature. For example, under normal conditions, sulphur, phosphorus are solids, bromine is a liquid, whereas hydrogen, oxygen and nitrogen are gases.
♦ Colour : Nonmetals come in many colours.
For example, sulphur is yellow, phosphorus is white, or red, chlorine is greenish-yellow, bromine is redish-brown. Hydrogen, oxygen and nitrogen are colourless.
♦ Appearance : Nonmetals have dull appearance i.e., they do not shine. However, graphite and iodine are the only nonmetals which have metallic lustre.
♦ Malleability and ductility : Nonmetals are neither ductile nor malleable. Nonmetals cannot be drawn into wires, and beaten into leaves/sheets.
♦ Conductivity : Nonmetals do not conduct heat and electricity, i.e., nonmetals are insulators. Graphite however, is a good conductor of heat and electricity.
♦ Density : Nonmetals usually have low densities and are soft. Diamond however is an exception. Diamond is the hardest natural substance known.
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