# Question Video: Understanding Element Symbols

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?

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### 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.