# Formula: Mass Defect Mass of the nucleus    Neutron number    Proton number

## Mass difference

Unit
The mass difference $$\class{brown}{\delta m}$$ of the individual nuclei components and the mass $$\class{brown}{m}$$ of the nucleus is not zero. This is called mass defect. This mass difference hides in the binding energy of the nucleus.

## Mass of the nucleus

Unit
Mass of the nucleus formed by the union of $$N$$ neutrons and $$Z$$ protons. The nucleus is lighter than the sum of its components (mass defect).

## Neutron number

Unit
Number of neutrons used to build a nucleus.

## Proton number

Unit
Proton number (atomic number) is the number of protons used to build a nucleus.

## Mass of a neutron

Unit
The rest mass of a neutron is: $$\class{brown}{m_{\text n}} ~=~ 1.674 \cdot 10^{−27} \, \mathrm{kg}$$

## Mass of a proton

Unit
The rest mass of a proton is: $$\class{brown}{m_{\text p}} ~=~ 1.672 \cdot 10^{−27} \, \mathrm{kg}$$

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