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 nature of matter and its transformations is fundamental to all branches of science.

• Atom: The atom is the basic unit of matter, consisting of a nucleus (protons and neutrons) and electrons.

• Matter: Anything that has mass and takes up space.

Classification of Matter

Pure Substances vs. Mixtures

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

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

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

Elements and Compounds

Atomic Composition

Pure substances are further divided into elements and compounds:

• Element: Made of only one kind of atom. Example: Oxygen (O2).

• Compound: Made of two or more different elements chemically bonded together. Example: 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 new substances with different properties. Example: burning wood.

Properties of Matter

Mass, Volume, and Intensive Properties

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

• Mass: The amount of matter in an object.

• Volume: The amount of space an object occupies.

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

• Intensive Properties: Do not depend on the amount of matter (e.g., density, boiling point).

Example Equation: Density

Density is an intensive property and is calculated as:

Example: Water has a density of approximately 1.00 g/cm3 regardless of the amount present.