Introduction to Chemistry

Definition and Scope

Chemistry is the scientific study of matter, its properties, and the changes it undergoes. It explores the composition, structure, and behavior of substances at the atomic and molecular levels.

• Matter: Anything that has mass and occupies space.

• Atom: The basic unit of matter, consisting of a nucleus surrounded by electrons.

Classification of Matter

Pure Substances and Mixtures

Matter can be classified based on its composition into pure substances and mixtures.

• Pure Substances: Have a fixed composition and distinct properties. Examples include elements and compounds.

• Mixtures: Consist of two or more substances physically combined. They can be separated by physical means (e.g., filtration, distillation). Example: salt water.

Elements and Compounds

Pure substances are further divided into elements and compounds:

• Element: A substance made of only one kind of atom (e.g., oxygen, O2).

• Compound: A substance made of two or more different elements chemically bonded together (e.g., water, H2O).

Physical and Chemical Changes

Types of Changes in Matter

Matter can undergo physical or chemical changes:

• Physical Change: Alters the form or appearance of matter but does not change its composition. Example: melting ice.

• Chemical Change: Results in the formation of one or more new substances with different properties. Example: burning wood.

Properties of Matter

Mass, Volume, and Intensive Properties

Properties are characteristics used to describe matter:

• Mass: The amount of matter in an object, measured in grams (g) or kilograms (kg).

• Volume: The amount of space an object occupies, measured in liters (L) or cubic meters (m3).

• Intensive Properties: Do not depend on the amount of substance present. Example: density.

Density is an important intensive property, defined as mass per unit volume:

• Extensive Properties: Depend on the amount of substance present (e.g., mass, volume).

Comparison of Intensive and Extensive Properties