Help with Isotopes

Question

Isotope: Sulfer-31

What is the isotope symbol?

Protons?

Neutrons?

Electrons?

I don't understand how to do isotopes at all.

Answer 1

Here is what you need to know to do isotopes. An isotope is an element with the SAME number of protons and electrons, but a DIFFERENT number of neutrons. So, the only difference between sulfur-31 and sulfur -32 is the number of neutrons. Look in the periodic table and find sulfur (S). It has an atomic mass of 32 and an atomic number of 16. So, the atomic number tells you # of protons (16). The atomic mass is the sum of the protons and neutrons. So, S-32 has 16 protons and 16 neutrons. The number of electrons is equal to the number of protons for all elements (they have no net charge). So S-32 also has 16 electrons.

Now, what about S-31. Since it is sulfur, it has to have 16 protons and 16 electrons. That is what defines it as sulfur. If it had any other number of protons, it wouldn't be sulfur. BUT, recall that atomic mass (31) is the sum of protons plus neutrons. So, S-31 must have only 15 neutrons (16 + 15 = 31). Get it?

Summary:

#protons = atomic number (ex: Na has 11 protons; C has 6 protons)

#electrons = # of protons (ex: Na has 11 electrons; C has 6 electrons)

#neutrons = atomic mass - # of protons (ex: Na-23 has 12 neutrons but Na-22 has 11; C-12 has 6 neutrons but C-14 has 8 neutrons)