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 vs. Mixtures

Matter can be classified based on its composition and the ability to separate its components.

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

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

Elements and Compounds

Pure substances are further categorized as elements or compounds based on their atomic composition.

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

• Compound: A substance composed 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: 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 (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), milliliters (mL), or cubic centimeters (cm3).

• Intensive Properties: Do not depend on the amount of substance present. Example: Density, which is calculated as:

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

Summary Table: Types of Properties