Do you have 11 protons? Cause you’re sodium fine.

Thirteen hours studying for my freshman biology final and I barely squeaked by with a C+. My high school languages classes were a breeze while algebra brought me to tears. But my sophomore chemistry class? Aced it! Why? Because my new, 20-something chem teacher was a serious hottie. Sleepy eyes, a young sense of a humor and olive skin – I could watch that woman point at a Periodic Table all damn day.

Basic sexual chemistry got this scientifically stunted student’s Bunsen burner blazing. Sexual chemistry works in mysterious ways – it makes us do things we never thought we would, attracts us to unexpected people and gets us grades we never thought we could get. But why?

1. You’ve got plenty of dirty words to say to someone, but nothing clean comes to mind:

Don’t have much to say besides “Spank me harder!”? The part of our brain that controls love is different than that which controls lust and sometimes they stay separate. According to Dr. Helen Fisher, author of Why We Love, this is a leftover evolutionary trait that drives us to mate but not date.

However, orgasms release oxytocin and dopamine, chemicals that trigger emotional feelings of closeness and attraction. So, if you exercise this initial lust enough (tough, I know), intellectual intimacy might follow. This is especially true in female brains which utilize oxytocin more frequently, powering the stereotype that women “can’t have casual sex” as easily as men.

2. One person feels the heat but the other’s left cold:

Simple social etiquette is to blame for this one-sided chemistry combustion. Women especially can find themselves dating someone for longer than they should simply to be polite. Combine one person’s social etiquette with another’s strong positive feelings and you’ve got easily misinterpreted signals that’ll unfairly string your measly mate along. Do both of you a favor and take out the emotional trash before it stinks up the place.

3. You totes hit it off on OKC but not IRL:

Falling for someone online but flopping off-screen is common – it’s too easy to only show our best sides via photoshop and spellcheck on online dating profiles.

And though we’d like to think that real beauty isn’t just on the outside the truth is, 80% of it kind of is – 80% of the stimuli that we take in is visual, making in-person interactions clutch in determining sexual chemistry.

4. Your initial spark fades over time:

Dr. Fisher calls this a “relationship survival trait”. If we forever acted the way we do when we first start dating someone new – missing deadlines, pulling all-night sexcapades, blowing off our friends – we’d crash and burn.

Our bodies and minds regulate these feelings after the initial pop to make our relationships more manageable for long-term love. If your fire fizzles when the initial frenzy fades, it’s not meant to last.

5. You’re like apples and oranges but you just can’t get out of their fruit bowl:

This “complementary chemistry” is to blame for the “ugly duckling/beautiful swan” phenomenon. We naturally seek partners who highlight our strengths and mask our flaws. The vapid vixen might date the genius goof because the nerd makes the knock-out feel smart and the beauty makes the brains feel sexy but really, the mismatched couples that last the longest are those that combine complementary chemistry with common interests.

6. Your friend makes you laugh so hard you trip and fall on their _____ :

Some of my favorite sexual interactions are with “ivy leaguers” – no, not brainy Harvard butches, but those platonic friends who sneakily grow on you until suddenly you find yourself wrapped up in their leafy-green sheets.

Research shows that laughter increases sexual attraction between people. Laughter releases the happy-drug dopamine in the brain, also responsible for our pleasurable response to addictive drugs and a close friend of adrenaline. The more fun you have with someone, the more the brain associates them with large amounts of dopamine which then increases sex drive and bam! – suddenly you’re doin’ it on the periodic table.