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What is the atomic number for helium?
The nucleus of the helium atom contains 2 massive, positively charged particles. Thus, ##Z##, the ##=## ##2##.
##Z## is simply the number of protons, massive, positively charged particles, present within the nucleus. ##Z## thus defines the identity of the element: ##Z=1##, hydrogen; ##Z=2##, helium; ##Z=3##, lithium;.................##Z=80##, mercury.
You do not have to remember these numbers, because in every exam you ever sit you should be provided a copy of , which lists all the in order of atomic number. Of course, you still have to be able to use the table.
Given the examples, ##Z=1##, hydrogen; ##Z=2##, helium; ##Z=3##, lithium;.................##Z=80##, mercury, how many electrons does each neutral element contain? Why?
