Pure substanes

pure substances have a definite chemical composition and definite physical and chemical properties. they are all homogeneous. eg- elements and compunds.

mixtures

Combinations of two or more substances that retain their individual properties and can be separated by physical methods. they do not have definite physical and chemical properties.

element

a pure substance which cannot be converted into anything simpler than itself by any physical or chemical processes. smallest unit is atom.

atomicity

the number of atoms present in a molecules of an element.

characteristic of compounds

• compounds are pure and homogenous substances

• they have definite melting and boiling points

• all samples of a pure compound have an identical set of definite physical and chemical properties.

• the components of compounds can only be separated by chemical methods.

• during formation of compounds energy is ether absorbed or liberated.

mixtures

a kind of matter which is formed by mixing 2 or more pure substances n any proportion, such that they do not undergo any chemical change and retain their individual properties.. they are impure substances.

characteristics of mixtures

• the components in a mixture vary in their proportions

• they can either be homogenous or heterogeneous

• the substances mixed together have no chemical combination between them.

• the components are loosely held together they hence retain their individual properties

• they do not have a fixed melting or boiling points.

• the components can be separated by simple physical methods

• no energy changes usually takes place during the formation.

• they cannot be represented by chemical formulas.

homogeneous mixtures

components are uniformly distributed throughout its volume and cannot be seen separately.

heterogenous mixtures

in this mixture the components are not uniformly distributed throughout the volume and can be easily seen separately.