The atomic number equals the number of protons and electrons (in a neutral atom)
Explanation:
An atom is composed of three types of particles:
- Protons: they are found in the nucleus of the atom. They are positively charged ([tex]q=+1.6\cdot 10^{-19}C[/tex]) and have a mass of approximately [tex]m=1.67\cdot 10^{-27}kg[/tex]
- Neutrons: they are also found in the nucleus. They have no electric charge and have a mass slightly larger than that of protons
- Electrons: they orbit around the nucleus. They have negative electric charge ([tex]q=-1.6\cdot 10^{-19}C[/tex]) and are much lighter than protons, having a mass of [tex]m=9.11\cdot 10^{-31} kg[/tex].
An atom is also identified by two numbers:
- Atomic number (Z): it is equal to the number of protons in the nucleus
- Mass number (A): it is equal to the number of protons+neutrons in the nucleus
For a neutral atom, the net electric charge is zero: this means that the number of protons equals the number of electrons. But since the number of protons corresponds to the atomic number Z, this means that the atomic number is also equal to the number of electrons, for a neutral atom.
Learn more about atoms:
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