Elements, atom, compound and molecules definition

Elements: the material that is made of the same building block (atoms) . It cannot be broken down into simpler substances by physical or chemical method .

Compound: different atoms joined together

Example: water molecule; it has two hydrogen atoms bonded to one oxygen atom 

The major difference between element and compound is that element are one or a group of similar atoms bonded together for example O2, Fe, and H2.

Compound on the other hand is formed of different type of atoms for example carbon dioxide CO2.

An atom: is the smallest part of matter that can still be recognized as that element.

Example: Carbon atom, oxygen atom, and iron atom.

Molecules: are the smallest units of element or compound that retain the characteristics of the compound.

Molecule contain group of atoms either similar atoms (like in element) or different atoms (like in compound). Examples for molecules: H2, H2O