Question

What is the isotope symbol for an atom that contains 82 protons and 125 neutrons?

Answer 1

Hint: From the number of protons we can find the number of electrons, so this will tell the atomic number of the element. With this atomic number, we can find the element from the periodic table. Now to find the mass number of the element, then we have to add the number of protons and the number of neutrons.

Complete answer:
The elements in the periodic table have two characteristics that are written along with the symbol of the element. These are an atomic number which is written as a subscript on the symbol and a mass number which is written as the superscript on the symbol.
We are given the number of protons and neutrons which can be used to find the symbol of the element.
From the number of protons, we can find the number of electrons, so this will tell the atomic number of the element. So, the element has 82 protons, this means that there is an 82 positive charge on the element. To balance it, there will be 82 electrons present, therefore, the atomic number is 82.
From the periodic table, lead is the element having atomic number 82.
Now to find the mass number of the element, then we have to add the number of protons and the number of neutrons. The given numbers of neutrons are 125, so the mass number will be:
Mass number = 82 + 125 = 207
The mass number is 207.
So, the symbol of the isotope can be written as ${}_{82}^{207}Pb$.

Note:
From NMR spectroscopy we can find the abundance of any element, so from the NMR spectroscopy it was found that ${}_{82}^{207}Pb$ is almost 100% abundant, and it is an important element.