Atoms and Molecules: Overview, Questions, Preparation

An atom is the smallest unit of matter. The word 'Atom' is a Greek word meaning indivisible. This is because atoms were once considered the smallest particle in the universe, which could not be divided further. Typically, an atom comprises two regions:

• The nucleus is located in the center of the atom and contains protons and neutrons.
• The outer region hosts the electrons in the orbits, which run around the nucleus. Each electron carries a negative charge (-1), while the proton has a positive charge (+1).

A molecule is the smallest unit of an element or a compound. It has the chemical characteristics of a Compound and exists independently in nature. A group of two or more atoms that are chemically bonded form a molecule. This molecule, in turn, reflects the properties of its substances. The number of atoms combined to form a molecule is known as the atomicity of the molecule.

A molecule of water (H2O) comprises two atoms of hydrogen and one atom of oxygen. On the other hand, an atom of oxygen is the basic unit formed with eight protons, eight neutrons, and eight electrons. Similarly, if three atoms of oxygen combine, they form O₃, which is ozone.

Both atoms and molecules together make up the entire universe. As mentioned earlier, the atoms come up together to form a molecule, but the atoms don’t usually carry the chemical properties when they form a molecule. A detailed study of structural chemistry concerned with Valence further determines the definite ratios in which the atoms combine to shape a molecule.