Compounds Compounds are pure substances that differ from elements because they contain more than one kind of atom. The Law of Definite Composition (or the Law of Definite Proportions) applies to compounds. For example, sodium chloride contains one atom of sodium for each atom of chlorine. Water contains two atoms of hydrogen for each atom

Isotopes: Isotopes are atoms of the same element having the same atomic number but different atomic masses. Note that the difference in the masses of isotopes is due to the different number of neutrons in their nuclei. Isotopes have the same chemical properties . because they have the same number of electrons. Isotopes have different physical

Atomic Number: Atomic number of an element is equal to the number of protons present in the nucleus of an element. Atomic number = number of protons in one atom of element. Since the atom as a whole is neutral therefore atomic number is the same as the number of electrons around the nucleus of