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Academia - Collins - Pocket Scientific Dictionaries - Chemistry
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atom
atome m

corn. The smallest, indivisible particle of an element, atoms form the building blocks of everything that exists in the world. Atoms are so small that if 100 million of them were placed one after the other, their length would not exceed 11 cm. The atom is composed of subatomic particles
Smaller ones are:

Protons (P) Neutrons (N)
These particles exist
In the center of the atom, that is, in the nucleus.

Electrons (e) move these particles
around the nucleus

The atom as a whole is electrically neutral, although protons and electrons carry electrical charges. These charges are equal in size and opposite in sign, so the number of protons is always equal to the number of electrons. Atoms that lose or gain electrons are called ions. Atoms of the same element contain the same number of protons and have the same atomic number. But atoms of the same element can contain different numbers of neutrons. See isotope.
An atom can be thought of as the smallest parts of an element that can react chemically.


atomicity
atomicity f

Atomicity. The number of atoms in an element's molecule. In inert gases, there is one atom in the molecule, and therefore its atomic number is 1. All other gases have an atomic number of 2, such as oxygen and nitrogen (N2), with the exception of ozone. Solid sulfur molecules have an atomic number of 8. (Sa).


atomic mass
Masse f automatically

Atomic mass. Atoms have different masses if they contain different numbers of protons, neutrons, and electrons. Because these particles are very small, the mass of the atom is negligible. It is not usual to refer to the mass of an atom in grams or kilograms, so we usually compare the mass of an atom with another standard mass, and this is called the relative atomic mass (A).


atomic number (Z)
number m automatic

Atomic number The number of protons in the nucleus of an atom. All atoms of the same element have one atomic number, meaning that each sodium atom contains 11 protons. The number of electrons in a neutral atom is equal to the atomic number.


Avogadro constant / number (L) constant / number m d'avogadro

Fixed/number of avo left. The number of atoms present in exactly 12 grams of isotope carbon-12, and more generally, is the number of molecules present in a mole of a substance.
L = 6 x 1023 mol -1


Avogadro's hypothesis/law
loi ƒ d'Avogadro

Hypothesis / Avogadro's Law This law states that equal volumes of gases contain, at the same temperature and pressure, the same number of molecules, meaning that both 10 cubic decimeters (dm3) of oxygen and an equivalent amount of hydrogen contain a similar number of molecules. This number is twice the number of molecules present in 5 cubic decimeters of chlorine, provided that all volumes are measured at the same temperature and pressure.