Question

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

Answer 1

`""_82^207Pb` or just `""^207Pb`.

Explanation:

The isotope of an element `X` is given by `""_Z^AX`, where `Z` is the proton number of the element and `A` is the mass number of the element.

The mass number of this isotope will be `82+125=207` units, while it has `82` protons.

Looking on the periodic table, element number `82` is lead, and its symbol is `Pb`.

Therefore, the isotope in this case will be written as:

`""_82^207Pb`

Alternatively, we can write it even shorter like this,

`""^207Pb`

since we know that lead can only have an atomic number of `82`.