In this video, we're going to calculate
the number of protons, electrons and
neutrons in an atom. Let's start with
fluorine which has a chemical symbol F.
Here are the information we pull out
from the periodic table. You should see
at least two numbers, one is a smaller
whole number and the other is a larger
decimal number. In the case of fluorine,
the smaller whole number is 9 that's the
atomic number abbreviated as Z. The
larger number 18.998, that's the
atomic mass, abbreviated as A. When
calculating the number of protons in an
atom, it's the same as the atomic number.
The number of electrons is also the same
as the number of proton as long as it is
for an atom which is neutral. For the
number of neutrons, it's the atomic mass
minus the atomic number. Keep in mind
that the number of neutrons should be a
whole number.
Meaning, no decimal points. Let's figure
out the number of protons, electrons and
neutrons for fluorine. You might want to
pause and calculate on your own first.
Okay, for number of protons it should
be the same as the atomic number which
is the smaller number, right? So, that
should be 9. Since the number of
electrons is the same as the number of
protons because we're calculating for F
atom it should be 9 as well. As for the
number of neutrons, it's the difference
between atomic mass and atomic number so
that turns out to be 19 minus 9 and
that's equals 10. Note that it is not
9.998 instead it is
10 because like I've mentioned the
number of any of the subatomic particles
protons, neutrons, electrons, they should
be whole number. Whole numbers are like
1, 2, 3, 4, 5, so on and so forth, no decimal
number. Let's move on to another example.
Let's say the question gives you
uranium-235 what does the 235 means?
That's actually the atomic mass of a
specific isotope, so, if we look at the
periodic table this is the information
we will get. The smaller number 92, that
the atomic number. What about 238? Well that's the average atomic mass.
Let's figure out the number of
protons, electrons and neutrons for
uranium-235. You can pause the video
while figuring out on your own. Okay, so,
the number of protons is the atomic
number which is 92 for a neutral atom.
The number of electrons is the same as
the number of protons so therefore it's
also 92 and for neutron, it's the
difference between atomic mass - atomic
number. Notice,  we're gonna use atomic
mass of this specific isotope so it's
going to give us 235 - 92 and that is
going to be 143. If you got 146, you
must have taken 238 - 90. That's a
common mistake.
The reason it's wrong is because this
example is asking us to find the number
of neutrons for uranium-235 isotope
therefore you're gonna have to subtract
it from 235 not 238. Moving on to our
third and final example.  14N. That 14
on the top left of nitrogen is the
atomic mass of nitrogen. In other words
we need to find the information for
nitrogen-14. Similar to the previous
example, since the atomic mass of the
isotope is already given, that's what
we're gonna use as our atomic mass, so ,we
pull out the information from the
periodic table for nitrogen and this is
what we got and it looks like isotope 14
is the most stable isotope since the
average atomic mass is pretty close to
the value of the isotope. So, the number
of protons and electron is going to be 7
and the number of neutron is going to be
14 minus 7 and that gives us 7. If you're
looking to calculate the number of
electrons in an ion be sure to watch out
for the upcoming video. To recap, for an
atom which is neutral the number of
electrons and protons are the same, which
is the smaller number in the periodic
table. The number of neutrons is the
atomic mass - atomic number meaning the
larger number minus the smaller number.
If the question is asking for a specific
isotope, be sure to use the given atomic
mass for that isotope. Last but not least
the number of protons, neutrons, electrons,
they should all be whole number, no decimal points.
Hope that was useful. Do
subscribe and thanks for watching!
