How do atoms relate to all matter

Structure of matter¶

Mass defect¶

The mass of an atom does not exactly correspond to the sum of the masses of the elementary particles, but is always slightly less. This loss of mass, which occurs when the building blocks are put together, is known as a mass defect.

The cause of the mass defect is the binding energy released when the elementary particles come together. According to Albert Einstein's famous formula - the equivalence of mass and energy - corresponds to the binding energy the difference the mass of the elementary building blocks and the entire atom, multiplied by the square of the speed of light :

Even a tiny mass defect corresponds to an enormous amount of energy.


  • The isotope consists of six protons, six neutrons and six electrons. Mathematically, the sum of the masses of all atomic building blocks would result in the following value:

    The actual mass of the isotope is only . The difference of is converted into energy during formation from the core building blocks. This mass corresponds to an energy of per atom respectively per gram of carbon. This corresponds to 22 million times the amount of energy that is released when one gram of coal is burned.

Mass defects only occur in nuclear reactions; in chemical reactions only the interaction of the external electrons is important.