Introduction to Chemistry

Definition and Scope

Chemistry is the scientific study of matter, its properties, and the changes it undergoes. Understanding chemistry is fundamental to exploring the composition, structure, and behavior of substances in the universe.

• 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. The two main categories are 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, evaporation). Example: salt water.

Elements and Compounds

Pure substances can be further divided into elements and compounds.

• Element: A substance made of only one kind of atom. Example: Oxygen (O2).

• Compound: A substance 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, each affecting substances in different ways.

• Physical Change: A change that does not alter the chemical composition of a substance. Example: Melting ice (solid water to liquid water).

• Chemical Change: A change that results in the formation of new substances with different properties. Example: Burning wood (wood reacts with oxygen to form ash, carbon dioxide, and water).

Properties of Matter

Mass, Volume, and Intensive Properties

Properties are characteristics used to describe and identify matter.

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

• Volume: The amount of space an object occupies, measured in liters (L) or cubic centimeters (cm3).

• Intensive Properties: Properties that do not depend on the amount of substance present. Example: Density ().