http://www.ck12.org Chapter 2. Matter
http://www.youtube.com/watch?v=6w7raarHNA8 (5:23)
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5074An Example: Hydrogen Isotopes
Hydrogen is an example of an element that has isotopes. Three isotopes of hydrogen are modeled in theFigure
2.68. Most hydrogen atoms have just one proton and one electron and lack a neutron. These atoms are just called
hydrogen. Some hydrogen atoms have one neutron as well. These atoms are the isotope named deuterium. Other
hydrogen atoms have two neutrons. These atoms are the isotope named tritium. For animated versions of these
hydrogen isotopes, go to this URL: http://www.s-cool.co.uk/a-level/physics/atomic-structure/revise-it/isotopes.
FIGURE 2.68
Q:The mass number of an atom is the sum of its protons and neutrons. What is the mass number of each isotope of
hydrogen shown in theFigure2.68?
A:The mass numbers are: hydrogen = 1, deuterium = 2, and tritium = 3.
Naming Isotopes
For most elements other than hydrogen, isotopes are named for their mass number. For example, carbon atoms with
the usual 6 neutrons have a mass number of 12 (6 protons + 6 neutrons = 12), so they are called carbon-12. Carbon