Classification of Substances – Maharashtra Board Class 7 Solutions for General Science (English Medium)
The properties of substances are determined depending on their atomic number and atomic structure.
|1.||A compound is formed by two or more elements combined in a fixed proportion by weight.||A mixture is formed by two or more substances mixed in any proportion.|
|2.||The proportion of constituent elements is fixed in a compound.||The proportion of constituent substances is not fixed.|
|3.||The compound has properties different from those of its constituents.||The constituents of a mixture retain their properties in the mixture.|
|4.||Chemical processes are used to separate original constituents from the compound.||Physical properties are used to separate substances from their mixtures.|
An alloy is a mixture of two metals or metals and non-metals. In an alloy, two or more elements are mixed to change the properties of the combining metals (or metal and non-metal). There is no chemical reaction between the two combining elements. Therefore, an alloy is a mixture.
All substances have different properties. Therefore, the classification of substances on the basis of their properties makes their study easy and convenient.
- In a compound, the constituent elements do not retain their properties.
- In a mixture, properties of constituents are retained.
- The chemical symbol of calcium is Ca.
- The molecular formula for carbon dioxide is CO2.
- The compound sodium chloride is made from the combination the elements sodium and chlorine.
- In the compounds H2O, NaOH, H2O2, hydrogen and oxygen are the common elements.
|Number of atoms of constituent elements||
|K:1, O:1, H:1
|(b)||Hydrogen peroxide||H:2, O:2||
|Iron chloride||Fe: 1, Cl: 2||FeCl2|
|(d)||Ammonium chloride||N:1, H:4, Cl:1||
|Copper sulphate||Cu:1, S:1, O:4||CuSO4|
|(f)||Magnesium oxide||Mg:1, O:1||
|Group ‘A’||Group ‘B’|
|(a) Sodium||3. Na|
|(b) Potassium||4. K|
|(c) Iron sulphide||2. FeS|
|(d) Sugar||5. C12H22O11|
|(e) Magnesium oxide||1. MgO|