Introduction to Chemistry

Definition and Scope

Chemistry is the scientific study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Understanding the composition, structure, and properties of matter is fundamental to chemistry.

• Atom: The atom is 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., salt water can be separated by evaporation).

Elements and Compounds

Pure substances are further classified as elements or 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 (solid water to liquid water).

• Chemical Change: Results in the formation of one or more new substances with different properties. Example: Burning wood produces ash, carbon dioxide, and water vapor.

Properties of Matter

Mass, Volume, and Intensive Properties

Properties are characteristics used to describe matter. They can be classified as extensive or intensive:

• Mass: The amount of matter in an object (an extensive property).

• Volume: The amount of space an object occupies (an extensive property).

• Intensive Properties: Do not depend on the amount of substance present. Example: Density () is the same regardless of sample size.