Structural / Molecular / Shorthand

I am going through a mock paper for an upcoming Science exam and I am struggling to understand a particular Question.

What is the structural formula, molecular formula and shorthand structure of 2-methylbut-2-ene ?

I tried watching Youtube video tutorials however, they automatically write the number down i.e C5H10 without explaining where the letters and numbers came from. I know that it is the molecular formula for 2-methylbut-2-ene so if it came up on the exam, I can remember that. However if 2-methylbut-2-ene didn't come up and it was something else then I wouldn't know what to put because I have no idea where the letters and numbers came from / how to work it out.

I'm feeling pretty stupid right now that I can't grasp this and it's very frustrating.

Where X is the number of carbon atoms in an alkene or alkane and Y is the number of hydrogen atoms in it, C_XH_Y is that molecule's molecular formula. Does that help?

Yes it does, thanks. How would I know how many carbons and hydrogens there are?

Yes it does, thanks. How would I know how many carbons and hydrogens there are?

For that you'll need to memorise the Latin roots that go into the names of molecules and groups. The prefix meth- means 1 carbon, eth- 2 carbons, prop- 3 carbons, but- 4 carbons, pent- 5 carbons, hex- 6 carbons, hept- 7 carbons, oct- 8 carbons, non- 9 carbons, and dec- 10 carbons. That's probably more than you'll need to know, but w/e. The number of hydrogens can be worked out from the number of bonds the carbons need to make. All carbon atoms make four bonds, which may be to other carbon atoms or to hydrogen atoms.

A couple of examples:

Pentane is an unbranched alkane containing 5 carbons, from the Latin root. Each carbon has four bonds, meaning that the carbons on the ends of the molecule are bonded to 3 hydrogen atoms each and the carbons in the middle of the chain are bonded to 2 hydrogen atoms each. 3+3+2+2+2 is 12, so pentane is C₅H₁₂.

2-methylbut-2-ene is a branched alkene containing butene and a methyl group. This makes it a bit trickier. It's often easiest to visualise or draw the structure of the molecule, keeping in mind that there are 5 carbons involved, each of which makes 4 bonds, and that a double bond counts as two bonds for each of the carbons that take part in it.