STD VIII – ELEMENTS COMPOUNDS AND MIXTURES (Online)

Introduction

An element is a pure substance that cannot be further broken down into smaller substances by chemical means. Elements can be classified into atoms and molecules. An atom is the smallest piece of an element. A molecule is made up of two or more atoms.

A compound is a substance made up of two or more elements, which are bonded chemically. A compound can be broken down into smaller substance by chemical means. The properties of compound differ from its constituent elements.

Example: Water is a compound made up of two elements hydrogen and oxygen.

Two or more substances physically combine together to form a mixture. It contains a mixture of molecules and atoms.A very good example of a mixture is air, which contains various gases in different proportions.

In this topic, you will learn more about elements, compounds, and mixtures.

Matter is built up of elementary particles namely, atoms, molecules and ions where an atom constitutes the basic unit of matter.

Matter may be homogenous [having the same composition and characteristics throughout] or heterogeneous [having different composition and characteristics throughout].

The homogenous matter is further classified into elements, compounds and mixtures.

Elements

The Term

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.

Compounds

The Term

A compound is a pure substance made up of two or more different elements [atoms] combined chemically in a fixed proportion.

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.

Mixtures

The Term

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.