Video Transcript
Which isotope is represented by
this nuclide symbol? The symbol consists of the letters
Na with 24 in the top left and 11 in the bottom left.
Nuclide notation is used to
summarize various features of elements, isotopes, and their atoms or ions. The first feature is a capital
letter or a capital letter followed by a lowercase letter, which is the element
symbol. The first step of digesting nuclide
notation is to look up the element symbol on the periodic table of elements.
In this case, the letters are
Na. A quick scan of the periodic table
will reveal that Na corresponds to an element in group one and period three. When we read that cell on the
periodic table, we find that Na is the symbol for the element sodium. So, we know our nuclide symbol has
something to do with sodium.
Now, sodium is an element. All atoms or ions of sodium consist
of a nucleus surrounded by an electron cloud. It’s the number of protons in the
nucleus of an atom or ion that determines the element. For sodium, that number is 11 which
we can tell from the atomic number on the periodic table. The atomic number is simply the
number of protons in an atom or ion of that particular element. And for sodium, that means 11
protons.
In nuclide notation, we put the
atomic number in the bottom left-hand corner. So, so far, we understand the
meaning of two of the terms in the nuclide symbol. It’s just the 24 in the top left
that’s mysterious. To understand that, it’s worth
looking at what an isotope is. In long form, an isotope is a type
of atom or ion of an element with a specific number of neutrons per nucleus. When we look up the element on the
periodic table, that only tells us the number of protons in the nuclei, not the
number of neutrons. For that, we need to know the
isotope.
To understand that, we need to
remember what this number in the top left-hand corner of the nuclide symbol is
for. In nuclide notation, the number in
the top left is known as the mass number. The atomic number is the number of
protons in an atom or ion of that particular isotope, while the mass number is the
number of protons plus the number of neutrons in an atom or ion of that particular
isotope. So, in this particular isotope, all
the atoms or ions have nuclei containing 11 protons and 13 neutrons. That’s 24 minus 11.
However, that doesn’t quite get us
to the end of the question. We need to know how to name this
particular isotope. When we name isotopes, we take the
element name, which tells us the number of protons. And then we take the mass number,
which we can use to calculate the number of neutrons. We know the element we’re dealing
with is sodium. And we can read the mass number 24
from the nuclide symbol. So, we worked out that an isotope
with this particular symbol means an isotope where each nucleus contains 11 protons
and 13 neutrons, and we call it sodium-24.
If you ever need to do this
quickly, this is what you can do. Look up the symbol on the periodic
table and find the name for the element. And then take the mass number in
the top left and put it after the element name with a hyphen. Using either method, you can be
sure that the isotope represented by this particular nuclide symbol is
sodium-24.
