Question

Using the periodic table, how would you determine the number of neutrons in 16 O?

Answer 1

Well the Periodic Table tells me UNEQUIVOCALLY, that the atomic number, `Z`, for oxygen is `8`, and thus the nucleus contains 8 neutrons.

Explanation:

How does this help us?

Well, we have the `""^16O` isotope. The nucleus of the isotope contains 8 protons (i.e. `Z=8`) unequivocally: this number of protons is what defines the element as an oxygen atom. But along with the 8 protons, the nucleus contains another 8 MASSIVE particles, i.e. 8 neutrons.......fundamental, massive `"nucular particles"` of NEUTRAL charge; the sum of the massive particles, neutrons, and protons, `8+8=16` gives the mass number of the isotope, which (as here) is commonly superscripted on the left of the element symbol. The `""^16O` isotope is the common one, and is approx. `99.8%` abundant (check this figure!).

`""^17O`, and `""^18O` isotopes are the next most common isotopes. Can you tell me here (i) how many protons in each isotope; and (ii) how many neutrons in each isotope?

Answer 2

`8` neutrons

Explanation:

the mass number is the number on the top-left of each element symbol that represents the sum of the number of protons and neutrons.
as stated in the question, this is `16` for `16O`.
the proton number is the number of protons and the number of electrons in the atom (not added together). this is on the bottom-left of each element symbol.
this is `8` for oxygen, no matter the number of neutrons.
number of neutrons = mass number - proton number
`= 16 - 8`
`=8`

therefore there are 8 neutrons.