chemistry note

Chemistry
Definition, Branches, Importance, and
Applications
1. Definition of Chemistry
Chemistry is the branch of science that studies matter, its composition, structure, properties,
reactions, and the changes it undergoes.

In simple words:

Chemistry is the study of substances, what they are made of, their properties, and how they
change into other substances.

For example, chemistry explains why iron rusts, water boils, wood burns, and acids react
with bases.




2. What Does Chemistry Study?
Chemistry mainly studies:

1. Matter

Anything that has mass and occupies space is called matter.

Examples:

 Water
 Air
 Soil
 Metals
 Plastic

2. Atoms

Atoms are the basic units of elements.

For example:

,  Hydrogen
 Oxygen
 Carbon
 Sodium

3. Molecules

A molecule is formed when two or more atoms are chemically bonded.

Examples:

 H₂O → Water
 O₂ → Oxygen
 CO₂ → Carbon dioxide

4. Chemical Reactions

Chemistry studies how substances change into new substances.

Example:

Hydrogen + Oxygen → Water




3. Major Branches of Chemistry
1. Organic Chemistry
Organic chemistry mainly studies carbon-containing compounds, especially those based on
carbon-hydrogen structures.

Examples:

 Methane
 Ethanol
 Petrol
 Plastics
 Many medicines




2. Inorganic Chemistry