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What is an atomic number?

Answer 1

Cameron Andrews

By definition, the number of protons in the nucleus.

This is irrespective of the charge of the atom as well. For a given atom, we denote its isotope as:

#""_(Z)^(A) X#

where:

So if I gave you oxygen-17,

#""_(8)^(17) O#,

it has #Z = 8#, and thus has #8# protons. Does it matter if I gave you #""_(8)^(16) O#, oxygen-16? Similarly, if I gave you

#""_(8)^(17)O^(2-)#,

how many electrons does it have? (Not #8#, but . . . ?)

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Answer 2

Ellie Andrews

The quantity of protons in the nucleus of an atom is its atomic number.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.