Atomic number

The atomic number of an atom is the number of protons in the nucleus of the atom.^[1]^[2] The atomic number of an atom defines which element it is. In a neutral atom, the atomic number is equal to the number of electrons orbiting the nucleus.^[1] The elements of the periodic table are listed in order of increasing atomic number.^[2]

Atomic number is not the same as:

atomic mass (symbol: m_a), which is the mass of a single atom, commonly expressed in unified atomic mass units
mass number (symbol: A), which is the sum of the number of protons and number of neutrons in the nucleus of an atom
relative atomic mass (also called atomic weight; symbol: A_r, ), which is the ratio of the average mass per atom of an element from a given sample to 1/12 the mass of a carbon-12 atom.

Atomic number is not changed by the number of electrons or neutrons; it is simply the proton number.

References

↑ ^1.0 ^1.1 Daintith, John, ed. (2008). A Dictionary of Chemistry (Sixth ed.). Oxford University Press. p. 48. ISBN 978-0-19-920463-2 .
↑ ^2.0 ^2.1 Moore, John T. (2010). Chemistry Essentials For Dummies. Wiley. p. 36. ISBN 978-0-470-61836-3 .

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[daintith-1] 1.0 ^1.1 Daintith, John, ed. (2008). A Dictionary of Chemistry (Sixth ed.). Oxford University Press. p. 48. ISBN 978-0-19-920463-2 .

[moore-2] 2.0 ^2.1 Moore, John T. (2010). Chemistry Essentials For Dummies. Wiley. p. 36. ISBN 978-0-470-61836-3 .

[1]

[2]

Atomic number

References

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