Atomic Mass:

The atomic mass, at times known as the atomic weight, of an element is around equivalent to the sum of the number of protons and the number of neutrons in the nucleus. This quantity is officially measured in atomic mass units (amu), where 1 amu is equivalent to exactly 1/12 the mass of the nucleus of the carbon isotope containing six neutrons. This is the most ordinary isotope of carbon and is represented as ¹²C or carbon-12. Any proton or neutron has a mass of around 1/12 amu, though neutrons are a little more massive than protons.

Elements are exclusively defined by their atomic numbers, though the atomic mass of an element depends on the specific isotope of that element. A familiar isotope of carbon, ¹⁴C, is found in trace amounts virtually in all carbon-containing substances. This fact has proven quite helpful to archaeologists and geologists. The isotope ¹⁴C is radioactive, while ¹²C is not. The radioactivity of ¹⁴C reduces with time according to a familiar predictable mathematical function. This make it possible for researchers to conclude whenever carbon-containing compounds were formed and therefore to find out how old various fossils, rocks, and artifacts are.

In nuclear reactions capable of generating energy, like the reactions which take place inside atomic bombs, stars, and nuclear power plants, a certain quantity of mass is forever given up-and transformed into energy-in the transactions among the atoms. This amount of mass can be exceptionally small yet generate a huge burst of energy. The very first person to formalize this relation was Albert Einstein, by using his famous equation

E = mc²

Where E is the energy generated in joules, m is the total mass in kilograms lost during the reaction, and c is the speed of light in meters per second.

The value of c² is enormous: around 90 quadrillion meters squared per second squared (9 x 10¹⁶ m²/s²). This is why too much energy can be generated by an atomic reaction between two elemental samples of modest mass.