1. How many neutrons does an O-18 atom have? A. 8, B. 10, C. 16, D. 18
QUESTION:
How many neutrons does an O-18 atom have? A. 8, B. 10, C. 16, D. 18
The mass number (A) is given as 18.
Mass number, A = N + Z
N = number of neutrons, Z = number of protons, or atomic number
Therefore, N = A – Z
SCRIPT:
How many neutrons does an Oxygen 18 atom have? A. 8, B. 10, C. 16, D. 18
PAUSE
CLICK
We’re given that the mass number is 18.
The mass number, which is often represented by the letter A, is the total number of neutrons and protons.
HIGHLIGHT A = N + Z In the equation shown here, N is the number of neutrons, and Z is the number of protons, which is just the atomic number.
We’re asked for the number of neutrons… so we rearrange the equation to solve for N.
N equals A minus Z.
A is 18
HIGHLIGHT A and 18
We can look up the atomic number for oxygen and find that it is equal to 8
CLICK HIGHLIGHT Z and 8
Therefore, the number of neutrons is 10.
18 minus 8 equals 10.
CLICK PAUSE END RECORDING
Look up: Z = 8, Therefore: N = 18-8 = 10

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08