What is the atomic number for helium?

1 Answer
Apr 2, 2016

Answer:

The nucleus of the helium atom contains 2 massive, positively charged particles. Thus, #Z#, the atomic number #=# #2#.

Explanation:

#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 the Periodic Table, which lists all the elements 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?