25-4-2020

Class 8A

Dear students,

Kindly go through these notes and write down important points.

After going through these notes do the questions send to you in your chemistry notebook.

Elements, compounds & mixtures

MATTER:

The matter is anything that occupies space, has mass and can be perceived by

our senses.

Matter is built up of elementary particles namely:

atoms, molecules and ions where an atom constitutes the basic unit of matter.

Matter can be broadly classified into elements, compounds and mixture

CLASSIFICATION OF MATTER:

Matter can be classified according to physical and chemical properties.

Elements

An element is a pure substance, made up of one kind of atoms only.

The atoms constitute the smallest particle of an element.

Elements cannot be converted or broken down into two or more simple

substances by physical or by chemical means.

EXAMPLES: Hydrogen (H2), Oxygen (O2), Sodium (Na), Calcium (Ca) , Silicon (Si)

etc.

Compounds

A compound is a pure substance made up of two or more different elements

[atoms] combined chemically in a fixed proportion.

• Examples: water, carbon dioxide, sugar, salt, etc.

Characteristics – of Compounds

Pure substance formed chemically from two or more elements.

Components in a compound are present in a definite proportion.

Compound is always homogenous [i.e. identical composition]

Particles in a compound are of one kind.

Compounds have a definite set of properties.

Component elements in the compound do not retain their original properties.

Components in a compound cannot be separated by physical means but by

chemical means only.

Formation of compound is always accompanied by energy changes.

Mixtures

A mixture is made up of two or more elements or compounds or both

mechanically mixed together in any proportion.

A mixture retains the properties of its constituent elements or compounds.

The components of a mixture can be separated by physical methods.

The properties of a mixture are in between those of its components.

• Examples of Mixtures: Tea, Perfume, Air, Sand, etc.

There are two types of mixtures:

1. Homogeneous mixture: uniform composition and properties

throughout.

2. Heterogeneous mixture: different composition and properties in

different parts of the mixture

CHROMATOGRAPHY

.

The principle of separating funnel is

that immiscible liquids separate out

in layers depending on their

densities.

It is used to separate mixture of oil and

water

Chromatography is a technique of

separating two or more dissolved solids

which are present in a solution in very

small quantities.