Introduction to General Chemistry

What is Chemistry?

Chemistry is the scientific study of matter, its properties, composition, and the changes it undergoes. It is a foundational science that explores the substances that make up the universe and the interactions between them.

• Matter is anything that has mass and occupies space.

• The atom is the basic unit of matter.

Classification of Matter

Matter can be classified based on its composition and properties. Understanding these classifications is essential for studying chemical reactions and properties.

• Pure substances have a fixed composition. Examples include elements and compounds.

• Mixtures consist of two or more substances physically combined and can be separated by physical means (e.g., salt water).

Elements and Compounds

All substances are composed of elements or compounds. Their classification depends on the types and combinations of atoms present.

• Elements are made of only one kind of atom (e.g., oxygen, O2).

• Compounds are made of two or more different elements chemically bonded together (e.g., water, H2O).

Physical and Chemical Changes

Matter can undergo changes that are classified as either physical or chemical. Recognizing the difference is crucial for understanding chemical processes.

• Physical changes do not change the composition of the substance (e.g., melting ice).

• Chemical changes result in the formation of new substances (e.g., burning wood).

Properties of Matter

Properties of matter are used to describe and identify substances. They are categorized as either extensive or intensive properties.

• Mass and volume are extensive properties because they depend on the amount of substance present.

• Intensive properties do not depend on the amount of substance (e.g., density).

Example Table: Classification of Properties

Example: Melting ice is a physical change because the composition (H2O) remains the same, while burning wood is a chemical change because new substances (such as CO2 and ash) are formed.