INTRODUCTION TO CHEMISTRY AND ATOMIC THEORY

Introduction to Chemistry

Chemistry is the branch of science that studies the composition, structure, properties, and changes of matter. It helps us understand what substances are made of, how they interact, and how new substances are formed.
It connects to other sciences such as biology, physics, and medicine — explaining everyday phenomena like cooking, rusting, digestion, and the use of medicines.

Chemistry is often called the central science because it links physical sciences with life sciences and applied fields like engineering and environmental science.

Atomic Theory

Atomic theory explains that all matter is made up of tiny, indivisible particles called atoms. These atoms combine in various ways to form all the substances we see.

• John Dalton (1808) proposed the first modern atomic theory, stating that:

  1. All matter is made of atoms.

  2. Atoms of the same element are identical, but different from those of other elements.

  3. Atoms combine in simple ratios to form compounds.

  4. Atoms cannot be created or destroyed in a chemical reaction.

Later discoveries — such as electrons (Thomson), the nucleus (Rutherford), and energy levels (Bohr) — refined Dalton’s model, leading to the modern atomic theory, which describes atoms as having a dense nucleus surrounded by electrons in specific energy levels or orbitals.