Why does sulfur have 18 neutrons?

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Check out the blackboard. That box on the left has all of the information you need to know about one element. It tells you the mass of one atom, how many pieces are inside, and where it should be placed on the periodic table. In the next section we're going to cover electron orbitals or electron shells. This may be a new topic to some of you.

Electrons In The Shells

Take a look at the picture below. Each of those colored balls is an electron. In an atom, the electrons spin around the center, also called the nucleus. The electrons like to be in separate shells/orbitals. Shell number one can only hold 2 electrons, shell two can hold 8, and for the first eighteen elements shell three can hold a maximum of eight electrons. As you learn about elements with more than eighteen electrons you will find that shell three can hold more than eight. Once one shell is full, the next electron that is added has to move to the next shell.

So... for the element of SULFUR, you already know that the atomic number tells you the number of electrons. That means there are 16 electrons in a sulfur atom. Looking at the picture, you can see there are two electrons in shell one, eight in shell two, and six in shell three.

Two hydrogen (H) atoms can bond with one sulfur (S) atom, making the formula H2S, also known as hydrogen sulfide. The same way that oxygen is happy when it has two extra electrons, sulfur likes to have two extras as well. See how the sulfur atom gets to share each of the electrons from the hydrogen atoms?

Two hydrogen (H) atoms can also bond with two sulfur (S) atoms, making the formula H2S2. That's just one more sulfur than H2S, but it's a totally different compound. See the name and how it's di-sulfide? The "DI" means two sulfur atoms. You can see that each of the sulfur atoms has eight electrons, and the two hydrogens have two electrons each. See how the electrons are shared?

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The atomic number, #Z#, specifies the number of protons, positively charged, massive, fundamental particles present in the sulfur nucleus. This number defines the sulfur atom as a sulfur atom (i.e if there were 17 protons, the atom would be chlorine).

For a neutral atom, if there are 16 positive nuclear charges, there must necessarily be 16 negatively charged particles, 16 electrons, whizzing about the nucleus.

Because electrons have negligible mass, to account for the mass of the isotope, there must be 16 neutrons, 16 neutrally charged, massive, fundamental particles present in the sulfur nucleus.

And thus finally, if we have the #""^32S^(2-)# ion, there are 18 electrons, 16 protons, and 16 neutrons.