A molecule is a microscopic thing which is made up of atoms. Atoms make up molecules, molecules make up particles and particles make up everything.
A molecule is the smallest particle of a substance which can exist by itself. If it was broken down any further then it would separate into atoms.
Molecules consist of atoms which are arranged in particular patterns. There may be as few as one atom in a molecule or over a thousand. A single water molecule is made up of one atom of oxygen to two atoms of hydrogen (which is why it has a chemical name of H2O).
But they are so tiny that a drop of water actually contains more than 33 billion billion molecules (approximately).
Molecules are always moving, even though we cannot see this movement. How fast they move and how close they are together defines whether the substance is a solid, a liquid or a gas. In a solid such as ice the molecules are close together and move very slowly. The molecules in a gas, such as steam move fastest and are the furthest away from each other.
The smallest particle of a pure substance, which can exist independently, is called a molecule. It may consist one or more atoms. For example He, Cl2, H2o. The molecules may be monatomic like He diatomic like Cl2, Hcl triatomic like Co2 etc. Molecules of elements contain same type of atoms. For example He, H2, O3, P4, S8. Molecules of compounds contain different kind of atoms. For example Co2, C6H16O6. The size of a molecule is bigger than atom because molecule contains May atoms accepting monatomic molecules. The size of the molecule depends upon the number of atoms present in it and its shape.
Very big molecules are called macromolecules. For example Hemoglobin. Each molecule of hemoglobin contains nearly 10,000 atoms and it is 68000 times heavier than a hydrogen atom. Hemoglobin is present in blood and helps to carry oxygen from our lungs to all parts of our body. Molecule of a pure substance is similar in all respects. They have empty spaces in between them; these are minimum in solids and maximum in gases. They have cease less movements and these are maximum in gases less I liquids while only to and fro motion is present in solids.
It is a group of atoms that are attached to each other