Isotopes Video Transcript
Hydrogen, helium, lithium, um, beryllium, boron, uh, nitrogen oh carbon. I always mess
that one up.
Dear Tim and Moby, How can two atoms of the same element have different numbers
of neutrons? From Gabriela.
Whoa good thing we got the periodic table of elements handy. Let’s look at an element
as it is represented on the table. How about oh say, chlorine. Cl is the symbol for
chlorine. The number above the symbol is the atomic number for chlorine. The atomic
number of an element tells you how many protons are in each atom. Every single atom
of chlorine in the universe has seventeen protons in its nucleus. The nucleus as you
can remember Moby, is the cluster particles of the center of the atom. It is made of
particles called protons and neutrons. This number is the atomic mass for chlorine and
it tells you how heavy chlorine atoms are compared with atoms of other elements. The
atomic mass is measured in atomic mass units or u, so chlorine’s atomic mass is
35.453 u. Well the atomic mass you see on the periodic table is actually just an
average mass. Not all atoms of a given element have the same atomic mass. So every
chlorine atoms has seventeen protons no matter what. But the number of neutrons can
vary. Some chlorine atoms have eighteen or even twenty neutrons. Isotopes are atoms
of the same element with different numbers of neutrons. Isotopes are called by its mass
number, the number of protons plus the number of neutrons in its nucleus. There are
two naturally occurring isotopes of chlorine. Chlorine-35 has seventeen protons and
eighteen neutrons. Chlorine-37 has also seventeen protons, but it has twenty neutrons.
About 75% of chlorine atoms are Cl-35 and about 25% are Cl-37. Chlorine-37 is
heavier than chlorine-35 because it has those two extra neutrons so there you go
isotopes in a nutshell.
Don’t I get a break yet? Hydrogen, helium, um, lithium, beryllium, um, boron, ahh,
carbon, carbon!