Atoms AND Molecules in Science

Everything around us is made up of tiny particles called atoms and molecules.

An atom is the smallest particle of an element that cannot normally exist independently and retains all the chemical properties of that element. Different elements have different types of atoms. The idea of atoms was first given by John Dalton in his Atomic Theory. He said that matter is made up of small particles called atoms, which are indivisible and indestructible. Atoms of the same element are identical in mass and properties, and they combine in fixed ratios to form compounds.

A molecule is a group of two or more atoms that are chemically bonded together. Molecules can be of elements or compounds. Molecules of elements contain the same type of atoms, such as O₂, N₂, and H₂. Molecules of compounds contain different types of atoms, such as H₂O, CO₂, and NH₃.

The chemical formula of a substance shows the composition of its molecules using symbols and numbers. For example, H₂O represents two atoms of hydrogen and one atom of oxygen.

Atoms or groups of atoms that carry a charge are called ions. Positively charged ions are called cations, like Na⁺ and Mg²⁺, while negatively charged ions are called anions, like Cl⁻ and SO₄²⁻.

There are two important laws of chemical combination:

1. Law of Conservation of Mass – Mass can neither be created nor destroyed in a chemical reaction.
2. Law of Constant Proportion – A chemical compound always contains the same elements in the same ratio by mass.

The mole concept is used to count particles such as atoms, molecules, or ions. One mole contains 6.022 × 10²³ particles, known as Avogadro’s number. The molar mass of a substance is the mass of one mole of that substance in grams.

In short, atoms are the building blocks of matter, and molecules are formed when atoms combine. Understanding atoms and molecules helps us know how substances combine and react to form new materials.