Define an element and provide examples.

(N/A) An element consists of only one type of particles. These particles may be atoms or molecules.
$1$. All atoms in an element are of the same type,but atoms of different elements differ in their nature.
$2$. Some elements,such as sodium $(Na)$ or copper $(Cu)$,contain single atoms as their constituent particles.
$3$. In other elements,two or more atoms combine to form molecules. For example,hydrogen $(H_2)$,nitrogen $(N_2)$,and oxygen $(O_2)$ gases consist of molecules where two atoms combine to form the respective molecule.