All GRE Subject Test: Chemistry Resources
Example Question #1 : Ions And Isotopes
Which atom has the same number of neutrons as an atom of ?
Elemental notation can provide you with a variety of information. The letter(s) indicate the element in question, the bottom number represents the atomic number (number of protons), while the top number represents the mass number (number of protons and neutrons). In order to find the number of neutrons in an atom, simply subtract the atomic number from the mass number. Doing this with our oxygen atom reveals that it has eight neutrons. The only answer option that has the same number would be the nitrogen atom, because 15 minus 7 is equal to 8.