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Chemistry - Atomic Number

Atoms of different substances have different numbers of protons in their nucleus. The number of protons in the nucleus is often referred to as the atomic number or proton number.

The atomic number indicates what substance it is. Atoms of the same substance usually have equal numbers of protons and electrons, so the atomic number also indicates how many electrons it has.

Each element has a specific set of chemical properties as a consequence of the number of electrons present in the neutral atom. The configuration of these electrons follows from the principles of quantum mechanics.

The number of electrons in each element's electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behaviour. Hence it is the atomic number alone that determines the chemical properties of an element; and it is for this reason that an element can be defined as consisting of any mixture of atoms with a given atomic number.

Atomic Structure

Atomic Number

Mass Number


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