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nucleon number (A)
number m nucléonique

nuclear number. The number of nuclei (protons and neutrons) in the nucleus of an atom. Since the mass of each of these particles is 1 atomic mass unit on the atomic scale, the number of nuclei is called atomic mass or mass number. The Nuclear number A is the sum of the number of protons and the number of neutrons, as shown in the table. The number of electrons in a neutral atom is equal to a number
Protons.

Particle -- A---- N ---- Z

Electron - ------ - ------ 0
Neutron 1 ------ 1 ------ 0
Proton 1 ------ 0 ------1
Helium atom 4 ------ 2 ------2

Isotopes of an element have the same number of protons but differ in the number of nuclei. This is because their nuclei do not contain the same numbers of neutrons.
On the other hand, isobars have the same value of A but different values ​​of N and Z.

Element ---- Nuclear type

Hydrogen --- hydrogen
----------------- Du Terium
----------------- Tritium

Helium --------- Helium - 3
------------------ Helium-4
------------------ Helium-6

All these atoms with special proton/neutron combinations are called nuclides.
In writing about atoms, nuclei, and nuclear interactions between them, we use symbols from three categories. The name of the element is given by its usual chemical symbol, and the value A is placed before the symbol and above the line, while before and below the line the value is placed 2. Thus, we write the six types mentioned in the table above as follows:

1/1H, 2/1H, 3/1H, 3/2He, 4/2He, 6/2He

235/92U is an isotope of metallic uranium. Its nucleus contains 92 protons (as in all uranium nuclei) and 143 (235-92) neutrons. The neutral atom of uranium-235 has 92 electrons in the cloud around the nucleus.


nucleus
noyau m

The nucleus of the precise central mass of the atom. The nucleus carries a positive charge because it contains positive protons. The mass depends on the number of neutrons and protons.
See nucleon number,

The nuclei of atoms and most ions have clouds of electrons around them. Electrons carry a negative charge. The number of electrons in the neutral atom cloud is equal to the number of protons in the nucleus.
The diameter of the nucleus is about 10-13 metres, which makes it much smaller than an atom, while the radius of the electron cloud is about 1,000 times larger than that. The cloud of electrons has a relationship with chemical reactions, while the nuclei have a fundamental role in determining the physical properties of each substance.

Likewise, the nucleus is the site of nuclear reactions. These reactions can transfer very large amounts of energy.
See atom bomb, nuclear power, and radioactivity.