How many covalent bonds is a sulfur atom most likely to form?

Question

Is it - 1,2,3,4, or 5 ?

Answer 1

Who asked you the question, and how sophisticated an answer are they looking for?  The problem is that to frame a correct and complete answer requires a lot of information that you're missing, it requires a context.  To be honest, the very act of phrasing the question this way belies a rather superficial understanding of chemical bonding generally and the behaviour of sulfur compounds specifically, and it reinforces a misleading impression that chemistry is just about handle cranking simple theoretical models rather than actually looking at real compounds.  In short: it's a bad question.

I suspect that whoever asked you the question is looking for the answer "2", because a ground state gas phase sulfur atom has 2 unpaired electrons, and because it's in the same group as oxygen, which most people would say tends to form two bonds.  But sulfur isn't oxygen.

Most likely in what sense, measured how?  A histogram of all known sulfur compounds?  Expressed as a mass percentage of all sulfur on the planet?   Most likely with what other element or elements, under what conditions?  How are you counting your bonds -- is a double bond just one bond, or is it two?

Is is true that H2S, and organic thiols or thioethers, have S atoms that look like O atoms: two bonds.  However, these are hardly the most common bonding modes for sulfur.

Many sulfur minerals (gypsum, epsom salt) and many common compounds (including sulfuric acid) are sulfates, containing ions of [SO4]2–, with each S bound to four O atoms, so that's four bonds -- maybe six if you count multiple bonds individually.

Another common mineral is galena, PbS.  Given the small electronegativity difference, that's best described as covalent bonding between the S and the Pb, and each S is tetrahedrally coordinated by four lead atoms: so again, four bonds.

Pyrite is usually described as an ionic complex containing [S2]2– anions, with a Lewis structure isoelectronic to that of Cl2.  It's a an S-S single bond.  One bond.

In the iron sulfur proteins used by pretty much every living thing for electron transfer reactions, S is bound to three iron atoms in a pyramidal arrangement.  Again, an electronegativity difference less than 1, so mostly covalent.  Three bonds.  Methionine bound to a copper or iron atom in a metalloprotein like plastocyanin or a cytochrome P450 has a sulfur with bonds to two C atoms and the metal: three bonds.

Combine carbon with a limited amount of sulfur, you make CS, the sulfur analogue of carbon monoxide.  That's a CS triple bond.  So three.

Combine S with dry oxygen, you get SO2, where a limiting Lewis structure shows formally a single bond to one O and a double to the other -- two bonding interactions, three bonds.  More O2 and a catalyst yields SO3.  Three interactions, four bonds.  Wet air gets H2SO4 again: four bonds.

Combine S with excess fluorine and you make SF6 every time.  Six bonds.  Not even a choice you were given.

A very common chemical in organic chemistry labs is dimethylsulfoxide, (CH3)2S=O.  One bond to each C, double bond to O, four bonds.

The only real answer is that there is no one answer, because S is simply too versatile in its behaviour.  Sulfur will form anywhere from 1 to 6 bonds, depending on the compound, the other elements, the surrounding conditions.  All these results can be explained in terms of simple bonding theories and basic principles of chemical behaviour.

Answer 2

2