The atomic number is the number of protons in the nucleus, so the atomic number is #10# (i.e. an atom of neon, #”Ne”#).
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The mass number is the total number of nucleons, which is the number of protons plus the number of neutrons.
We”re not given how many neutrons are in the atom, so we can”t necessarily know this..
Additionally, if we wanted to figure out the ionic charge of this atom, we subtract the number of electrons from the number of protons:
#”ionic charge” = 10-12 = ul(-2#
#Z#, #”the atomic number”#, specifies the number of protons, positively charged, massive particles, present in in the element”s nucleus. #Z# specifies the identity of the atom. If #Z=10#, we gots the element #”neon”#.
The NEUTRAL element contains precisely the same number of negatively charged extra-nuclear particles, that are conceived to whizz about the nuclear core; and of course these are the #”electrons”#. And thus we have a very unusual ion here, because there are more electrons than protons, and the atomic particle therefore has an associated electric charge, i.e. here we gots #Ne^(2-)#, or #””^20Ne^(2-)# to specify a likely individual isotope.
Atomic mass depends on the number of nucular particles, the aforementioned protons, but also #”neutrons”#, massive nuclear particles of ZERO electric charge, that also comprise the nucleus. Interactions between protons and neutrons, at impossibly short nuclear ranges, are strong enuff to overcome electrostatic repulsion between like charges, and bind the nucleus together. This is something you won”t learn about in a chemistry class. For #””^20Ne# we have assumed that the nucleus contains 10 neutrons; were 11 neutrons present, we would have #””^21Ne#.
Historically, the electrons were assigned a negative electric charge. It would have been so much more convenient, had electrons been assigned a POSITIVE charge, and thus protons would have therefore been assigned a NEGATIVE charge. It would have saved generations of quantum chemists from getting the right magnitude but wrong sign in their answer, just because they counted odd instead of even or vice versa in their calculations on many electron systems. Of course, the particle physicists would complain, but they are weird enuff, and few enuff in number to deal with the change. C”est la vie.