Changes are of two types - physical and chemical.
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.
Melting of ice, breaking of glass, tearing of paper, cutting of wood and changing of water to water vapour.
A permanent change in which a new substance is formed that has properties, which are different from the original substance”.
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.
Substance which contains two or more different kinds of particles.
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 are the elements which readily lose electrons to form positive ions or cations.
- Good conductors of heat and electricity
- 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.
- 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.
- Can be broken down into constituent elements
- Distinct set of properties
- Sharp melting and boiling points
A mixture in which various constituents are not mixed uniformly.
- 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.