Basic chemistry

What is the atomic nucleus explain it?

Mass and structure of atomic nucleus

What is the atomic nucleus?

The atomic nucleus :

The atomic nucleus constitutes the heart of the atom . Ernest Rutherford was the first to highlight it. Located in the center of the atom , it has a diameter of around 10 -15 meters, compared to 10 -10 meters for the atom as a whole.

Mass and structure of the atomic nucleus

The nucleus contains some 99.97% of the mass of an atom. The density of matter in an atomic nucleus is around 230,000 tonnes per cubic millimeter!

The nucleus of atoms is made up of:

  • protons;
  • neutrons.

Protons and neutrons are also called nucleons . The atomic nucleus is therefore positively charged and its cohesion is essentially ensured by the strong interaction .

Number of protons and number of neutrons

The number of protons in an atomic nucleus defines the chemical element . It is noted Z and called atomic number .

The number of neutrons can vary to give rise to isotopes of the element. Thus, the carbon 12 and carbon 14 are two carbon isotopes. They both count 6 protons, but the first counts 6 neutrons while the second counts 8.

Marie Curie, here in her laboratory, discovered the radioactivity of the atomic nucleus of radium.
Atomic nucleus


Stable nuclei, unstable nuclei

When the binding energy of an atomic nucleus is large enough, the nucleus is said to be stable. When it is too low, it causes instability. An unstable atomic nucleus is called a radioactive nucleus .

It emits a radiation α (alpha) and β ( beta ), usually accompanied by an emission γ (gamma) emission of photons . The number of protons – and neutrons – then changes. There is transmutation from one element to another. For example, a polonium atom 210, which has 84 protons and 126 neutrons, can become, by α radioactivity , a lead atom 206 containing 82 protons and 124 neutrons.

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