Question

Three isotopes of oxygen are oxygen-16 oxygen-17 and oxygen-18. Write the symbol for each, including the atomic number and mass number

Answer 1

The symbol of an isotope is:
$^A _Z X$
A - the mass number
Z - the atomic number
X - the symbol of an element

The symbol of oxygen is O.

The atomic number is the same for all isotopes of one element. For oxygen it's 8, because every atom of oxygen has 8 protons in its nucleus.

The mass number is the number of nucleons (protons + neutrons) in the nucleus of an atom, and it's given in the name of an isotope. Oxygen-16 has the mass number 16, oxygen-17 has the mass number 17, oxygen-18 has the mass number 18.

Oxygen-16: $^{16} _8 O$

Oxygen-17: $^{17} _8 O$

Oxygen-18: $^{18} _8 O$