10 -15 m. This unit of measurement is called as Fermi and is written as fm. It has to be noted here that both the nucleus as well as the atom is not a point like particle, but has a certain definite size or dimensions. From our above discussion, we can see that an atom of any element would weigh very less. It has been an established convention in Physics, to say that the atomic weight of an element is a number representing the sum of the constituent protons and neutrons. Table below lists some of the atomic weights of elements.
Atomic weight is a pure number.
The number of protons Z is called the atomic number. Z. Thus Hydrogen with 1 proton is vastly different from Oxygen which has 8 protons. 92 elements occurring in nature have Z going from 1 to 92. The heaviest element is Uranium with 92 protons. Neutrons, since they are electrically neutral, very indirectly affect the properties of elements, although their contribution to the nuclear structure is significant.