(a) What is an atom? How do atoms usually exist?
(b) What is a molecule? Explain with an example.
(c) What is the difference between the molecule of an element and the molecule of a compound? Give one example of each.
(a) Atoms are building block of all matter. They are the smallest particle of elements that can take part in a chemical reaction. They exist in combined form i.e., in the form of molecules and ions.
(b) Molecule is made up of atom and it is the smallest particle of a substance which has the properties of that substance. It can exist in a free state.
Example: Oxygen atoms combine to form O3 molecules.
(c) Molecule of an element consist of two or more atoms of the same element chemically bonded together whereas molecule of a compound consist of two or more atoms of different elements chemically bonded together.
Example for molecule of an element is that bromine atoms are covalently bonded to give a molecule of bromine Br2
Example for molecule of a compound is one atom of nitrogen and three atoms of oxygen chemically bonded together to form HNO3.