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CBSE - IX
Types of Substances
Types of Substances
Changesare of two types- Physical and ChemicalChanges are of two types - physical and chemical.
Physical change:
A temporary change in which the composition of the substance remains the same and no new substance is formed but only a change of state occurs.
Examples:
Melting of ice, breaking of glass, tearing of paper, cutting of wood and changing of water to water vapour.
Chemical change:
A permanent change in which a new substance is formed that has properties, which are different from the original substance”.
For example:
Formation of water, rusting of iron, burning of wood, lighting of fire crackers, burning of a match stick.
Pure Substance: A substance which is made of one kind of particle.
Examples - iron, aluminium, silver and gold.
Mixtures:
Substance which contains two or more different kinds of particles.
- Homogeneous in nature.
Cannot be broken down into simpler substances.
An atom is the smallest unit and shows all the properties of an element
Have a sharp melting point and boiling point.
- Classified into three classes as:
- metals
- non-metals
metalloids
Metals are the elements which readily lose electrons to form positive ions or cations.
Lustrous
- Good conductors of heat and electricity
Malleable
Ductile
Sonorous
- Almost all metals are solids except mercury which is a liquid at room temperature.
The elements which readily gain electrons to form negative ions or anions.
Non lustrous
- Bad conductors of heat and electricity
- Not malleable
- Not ductile
- Not sonorous
- Exist in all the three states
A pure substance composed of atoms of two or more elements that are chemically bound with one another in fixed proportions
A molecule is the smallest particle of a compound with properties similar to that of a compound.
- Homogeneous in nature
- Can be broken down into constituent elements
- Fixed composition
- Distinct set of properties
- Sharp melting and boiling points
A mixture in which various constituents are not mixed uniformly.
Homogeneous Mixture
- A mixture in which various constituents are mixed uniformly.
- Properties of homogeneous mixture
- Variable composition.
- Constituents are seperable.
- No new substance is formed.
- Energy is neither given out nor absorbed.
- Mixture does not have a sharp melting or boiling point.
