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What is an ISOTOPE?
We all know what an atom is by now and we are aware that all matter is made up of them. Atoms
themselves are made up of three subatomic particles: protons, neutrons, and electrons. Each of those has
different charges. The protons (positive) and neutrons (no charge) are found in the densest area of the atom.
That area is the nucleus. The electrons (negative) are the smallest part of the atom and can be found in electron
clouds outside the nucleus. They are so small that they are not even included in the atom‛s atomic mass number.
An atom with a mass number of 12.34 could gain three electrons and still have a mass number of 12.34. Only the
protons and neutrons are counted in that number.
The atomic number tells you how many protons are in the atom that makes up an element. For example,
Helium has an atomic number of 2 so Helium has two protons. Since all atoms on the Periodic Table are neutral,
Helium also has two electrons. Remember, if an atom has 43 protons, it also has 43 electrons. The number of
protons for a given atom of a specific element will never change. If Helium gained a proton, it would no longer be
Helium. It would be Lithium. If you change the number of protons, you change the element completely.
Back to the atomic mass number…the mass number tells you how “heavy” the nucleus is. It‛s a measurement
of the number of protons and neutrons. Sometimes atoms will gain a few neutrons. It‛s like gaining a few extra
calories or putting on some extra pounds. If the mass number changes (and we know the mass number is protons +
neutrons), we know it has to be because of the change in the number of neutrons. Remember, the number of
protons can‛t change or the element changes. When this happens, the atom is called an ISOTOPE. An isotope is
when an atom gains or loses neutrons. It‛s the same atom but it now has a different number of neutrons than
originally found on the Periodic Table in the back of the textbook. If you look at ten different Periodic Tables, you
will probably get at least four different mass numbers for each element. The mass number found on Periodic
Tables is just an average of all the possible isotopes for each atom of an element.
Isotopes are written with the element name and a number. The number written after the element‛s name is
the mass number. You will use this number to calculate the number of neutrons in the atom. You will need to use
the Periodic Table to find the element‛s atomic number (number of protons or electrons), but use the new mass
number to find the number of neutrons (when you‛re ready to complete the handout for today). For example,
Helium has a mass number of 2. It would be written like: Helium—2. The two written after the element name is
the mass number you need to use. Helium—4 has 2 protons, 2 neutrons, and 2 electrons. An isotope, Helium—6,
would have 2 protons, 4 neutrons, and 2 electrons. Only the number of neutrons is affected in an isotope.
Why do isotopes exist? Isotopes are the elements that can help us judge the age of the material that is
made up of the isotopic element. For example, the age of the trees that existed from several years back can be
calculated from the carbon isotope that constitutes the tree. Isotopes are chemical species of the same element
with a different number of neutrons. Isotopes of hydrogen have the names of deuterium and tritium. Hydrogen
has one proton. Deuterium has one proton and one neutron. Tritium has one proton and two neutrons. Tritium is an
unstable isotope of hydrogen and undergoes radioactive decay. When the number of neutrons present in the
nucleus is more, the nucleus is said to be unstable and it will lose the particles inside in the form of radiation. The
time taken for the compound present to become its half amount by the decay process is called the half-life period.
All the isotopes are not radioactive. Only some isotopic forms are unstable and undergo decay. In nature,
many forms of isotopes for every element exist. How they exist is not explained. Their existence is taken for
granted in nature. But artificially, there are certain methods discovered to generate isotopes that we require.
This is the way by which we are creating atom bombs which release a lot of energy by decay or emission.
Now you are ready to complete the handout. It should take you all period. Be respectful and stay quiet. If
you are in my homeroom, you better be very respectful today because you did not get a good report yesterday!