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Chemistry / 01

Basic Concepts of Chemistry

Chemistry begins with a simple idea: matter is made of particles, and those particles combine in measurable ways. This foundation gives us the language needed to understand chemical reactions and calculations.

1. Matter and Its Composition

Matter is anything that has mass and occupies space. Chemistry studies the composition, structure, properties, and changes of matter.

Element

A pure substance consisting of atoms with the same atomic number.

Compound

A substance formed when two or more different elements combine chemically in a fixed ratio.

Mixture

A physical combination of substances in which the components retain their individual identities.

2. Atoms, Molecules and Ions

An atom is the smallest unit of an element that retains its chemical identity.

Atoms can combine to form molecules, while atoms or groups of atoms carrying a net electrical charge are called ions.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

3. The Mole

Individual atoms and molecules are extremely small, so chemistry uses the mole as a convenient counting unit.

One mole contains approximately 6.022 × 10²³ particles. This number is known as Avogadro's constant.

Avogadro's relation

N = nNA

Here, N is the number of particles, n is the amount of substance in moles, and NA is Avogadro's constant.

4. Molar Mass

Molar mass is the mass of one mole of a substance. It is commonly expressed in grams per mole.

Amount of substance

n = m/M

Where n is the number of moles, m is the given mass, and M is the molar mass.

Example

If a substance has a molar mass of 18 g/mol, then 36 g of that substance corresponds to:

n = 36 / 18 = 2 mol

5. Stoichiometry

Stoichiometry is the quantitative study of the relationships between reactants and products in a chemical reaction.

A balanced chemical equation provides the mole ratio between substances involved in the reaction.

Example

For the reaction:

2H₂ + O₂ → 2H₂O

The mole ratio of hydrogen to oxygen to water is 2 : 1 : 2.

6. Concentration

Concentration describes how much solute is present in a given amount of solution.

Molarity

C = n/V

Here, C is concentration in mol/L, n is the amount of solute in moles, and V is the volume of solution in litres.

Key Ideas

The basic language of chemistry rests on a few important relationships:

Mass → moles → particles

These conversions allow chemists to move between measurable quantities and the microscopic world of atoms and molecules.

Balanced equations → mole ratios

Chemical equations provide the quantitative relationships needed to calculate reactants and products.