Video Transcript
A platinum atom has the chemical
symbol platinum-195. How many protons does the platinum
atom have? How many neutrons does the platinum
atom have?
Taking a look at this chemical
symbol, we see that capital Pt is the abbreviation for platinum. In order to answer these questions
about the number of protons and neutrons the platinum atom has, we’ll need to
understand these numbers to the left of this abbreviation.
We see this number to the lower
left 78. This is known as the atomic number
of the element. It tells us the number of protons
in the nucleus. It’s this number that gives the
element its identity and helps us find it on the periodic table. Since the atomic number is the
number of protons in the nucleus, that gives us the answer to our first
question. The answer is 78.
To answer the second question about
the number of neutrons in this atom, we’ll need to look at the number to the top
left. In general, this is referred to as
the mass number of an isotope. Just as the atomic number was equal
to something else, it was equal to the number of protons in the nucleus, so the mass
number represents something else as well. It’s equals to the number of
protons plus the number of neutrons in the nucleus.
In order to find the number of
neutrons in this platinum atom then, we can perform some subtraction. If we take the mass number of this
atom and subtract from it the atomic number, then that will give us the number of
protons plus the number of neutrons minus the number of protons. Altogether then, that will yield
the number of neutrons, the answer to the second part of our question.
We see that the mass number of this
atom is 195. And then, atomic number, the number
of protons, is 78. 195 minus 78 is equal to 117. This then is the number of neutrons
in this platinum atom.
