Chemistry: Pure Substances and Mixtures

Matter may be defined according to their composition as

pure substances or mixtures.

Pure Substances

A kind of matter with a definite or fixed composition. It is

made up of a specific number of atoms or groups of atoms

that are combined through a chemical reaction.

a. Elements

The simplest form of matter and is made up of only

one kind of atom, it cannot be decomposed into

simpler forms by physical or chemical means.

There are 118 elements known to exist arranged in

the periodic table of elements. 94 of these are

naturally occurring, while 24 are synthetic.

Periodic Table of Elements

A useful tool that can help in identifying elements

that exhibit similar properties.

1. Metals

Are solid at room temperature; lustrous,

malleable, ductile, and are the best

conductors of heat/electricity.

2. Nonmetals

Are the opposite of metals; gaseous or full

solids.

3. Metalloids/Semimetals

Ehibit properties of both metals and

nonmetals; they conduct heat and

electricity but are not as good as metals.

Also called semiconductors.

b. Compounds

Composed of two or more different elements that

are combined in a fixed ratio by a chemical

reaction.

The properties of elements that make up a

compound are different from the properties of the

compound formed.

Mixtures

Consist of two or more pure substances that are physically

combined, no chemical reaction between the components as

they retain their characteristic properties when mixed

together.

Each component doesn’t have definite proportions and

definite properties, they depend on the substances that are

present in it.

a. Homogenous Mixture

A mixture of substances that are evenly distributed

all throughout. The components cannot be

distinguished from each other by the naked eye.

Solution

Composed of two components:

1. Solute

The substance that is dissolved by another

substance, it exists in smaller amounts.2. Solvent

The dissolving medium in which the

solute dissolved is much more abundant.

b. Heterogeneous Mixture

Consists of substances that are not evenly

distributed all throughout. The components can be

distinguished from each other by the naked eye.

1. Colloids

A heterogeneous mixture with particles

that are bigger than those in a solution but

smaller than those in suspension.

The particles do not settle at the bottom

even after being left to stand for a long

time, they exhibit the Tyndall effect.

2. Suspension

A heterogeneous mixture with suspended

particles that are large enough to be seen

by the naked eye. The particles settle at

the bottom due to gravity.