Mass number

The mass number (A), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It determines the atomic mass of atoms. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion. The mass number is different for each different isotope of a chemical element. This is not the same as the atomic number (Z) which denotes the number of protons in a nucleus, and thus uniquely identifies an element. Hence, the difference between the mass number and the atomic number gives the number of neutrons (N) in a given nucleus: N=A−Z.

The mass number is written either after the element name or as a superscript to the left of an element's symbol. For example, the most common isotope of carbon is carbon-12, or 12C, which has 6 protons and 6 neutrons. The full isotope symbol would also have the atomic number (Z) as a subscript to the left of the element symbol directly below the mass number: 12
6
C
. This is technically redundant, as each element is defined by its atomic number, so it is often omitted.

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Latest News for: mass number

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Yahoo Daily News 22 Mar 2025
Hamilton emerged from his car after the finish line to a crescendo of cheers from the massed Shanghai fans who unfurled huge banners displaying the Englishman's number 44 ... "It felt great today, I got a good start ... dh/pst. .

Hamilton hails 'really special' first Ferrari win at China GP sprint

The Peninsula 22 Mar 2025
Shanghai ... Hamilton emerged from his car after the finish line to a crescendo of cheers from the massed Shanghai fans, who unfurled huge banners displaying his number 44. "That is a really, really special weekend so far," the 40-year-old told reporters.

Oscar Piastri takes Chinese GP pole after Lewis Hamilton secures first Ferrari win in sprint

Independent online (SA) 22 Mar 2025
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Hindustan Times 22 Mar 2025
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Piastri on Chinese GP pole after Hamilton takes first Ferrari win in sprint

Urdu Point 22 Mar 2025
... displaying his number 44.</p><p> - 'Really special weekend' -</p><p> "That is a really, really special weekend so far," the 40-year-old Englishman told reporters.

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‘Tagged Olive Ridleys still in coastal waters, not deep sea’

The Times of India 21 Mar 2025
Mass hatching is expected towards the end of April. 'We have been noticing sporadic hatching, whose number roughly would be 2,000. But mass hatching is yet to start and they are expected sometime in the ...

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