Understanding of an element, molecule and compound
Element is a pure substance composed of atoms. Atoms combine to form molecule or compounds. Compound is always made of different atoms while a molecule can be made of either similar or different atoms.
Atoms, Molecules and Ions
An element is composed of extremely small particles called atoms. All the atoms of an element are identical. The atoms of different elements are different and exhibit different properties. Atoms of an element cannot be converted into atoms of another element; nor they can be created or destroyed in normal chemical reactions.
When two or more atoms of the same or different elements combine it is called a molecule. Example: H2, O2 are molecules of same element hydrogen and oxygen respectively while, H2O is a molecule of two different elements: hydrogen and oxygen. Compounds are formed when atoms of different elements combine. Example: H2O, CO2. In other words, compounds are molecules of different elements.
When the particles in the combined atoms gain energy, they break the bonds and form charged species called ions. Negatively charged ions are called anions while positively charged ions are called cations. Their generation is due to unequal sharing of electrons and the process is called ionization.
A French chemist Antoine Lavoisier (1743–1794), known as the 'Father of modern chemistry' laid its foundation. Lavoisier accepted the idea of an element as any material made of only one component. He identified a compound as any material composed of two or more elements.