|Left: a 2010 depiction of the chemistry of love: two heart-shaped climber’s hooks attached to together, signify a human chemical bond, by Indian blogger Prashant Mishra, who describes love as an action of beauty upon the heart, being an exothermic reaction (ΔH < 0), resulting in faster heart beat, wherein two complex compounds (boy and girl) unite, through the help of certain catalysts (friends, cousins, movies, restaurants), reducing agents (parents, neighbors, teachers, and society).  Right: a 2011 DeviantArt.com poster depiction of the “chemistry of love” alluding to some hypothetical chemistry student meandering thoughts on the nature of love in terms of protons and electrons, chemical bonding or nuclear bonding, changes in atomic mass, or something along these lines. |
“You can’t force chemistry to exist where it doesn’t in the same way you can’t deny it when it does.”— Anon (c.2014), Pinterest quote (Ѻ) from Xushandwiz.com
Kinetic factors | Thermodynamic factors
The following infelice.tumblr.com image on Pinterest (Ѻ) highlights the so-called “kinetic factor” as compared to the “thermodynamic factor” involved in reactions between people:
In other words, per collision theory arguments, two people may be thermodynamically feasible to bond, but the alignment of their reaction trajectories may be off or misaligned in time.
The earliest ideas on the chemistry of love can be found in early Egyptian poems, alluding to ideas on chemical bonding. One circa 1000BC poem speaks, for instance, of how "the nets of your love have trapped me". 
Into the Middle Ages, the Greco-Roman story of Cupid and Psyche evolved into the myth of Cupid carrying two sets of arrows: one set gold-headed, which inspire love; and the other lead-headed, which inspire hatred. In modern chemical terms, gold acts as secondary field particle as nuptial gift to inspire love, whereas lead is a poison.
Into the latter half of the second millennium, the theory of love potions was invented, supposing that a drink of a certain mixture could a suitor fall in love.
In 1809, German polymath Johann Goethe was the first to use a standard physical chemistry textbook to formulate a standard theory of love, based on the logic affinity chemistry and affinity reactions.
in 1922, the "chemical reaction theory of love", the view that “love is in its ultimate analysis nothing but a chemical reaction”, was established in the minds of typical scientists. 
With the rise of the field of neuroscience and the initiation of neurochemistry, the study of the chemicals of the brain, new chemical based theories of love began to crop up. A few of these are listed below in chronological order:
● Pheromone theory of love (1959)
● Endorphin theory of love (1976)
● Chocolate theory of love (1980)
● Oxytocin theory of love (1992)
New models are starting to focus on other neurochemicals such as serotonin or dopamine, etc., as well as neuroimaging, e.g. fMRI images of couples in love vs. people not in love.
|Left: Time magazine's famous 1993 cover story article "The Chemistry of Love", arguing that love is a function of (a) imprinting, bonding characteristics familiar from youth, (b) attraction, governed by phenylethylamine (PEA), dopamine, and norepinephrine, types of amphetamines, and (c) attachment (John Bowlby's theory), a function of endorphin (endorphin theory of love), the runner's high, and oxytocin (oxytocin theory of bonding), the cuddle chemical. Center: an artistic rendition of the so-called "love addict", modeled on the idea that people need to get their love fix from other people the way a junkie gets his or fix from his or her dope dealer. Right: a chemistry of love art T-Shirt design by Wenceslao Almazan. |
The standard model of the chemistry of love, as of 2007, holds that (a) a human is a molecule (a human molecule), and (b) that “love” or rather two people falling in love into a relationship is a chemical reaction, pure and simple, and (c) human reactions, such as love the chemical reactions, are governed by the Lewis inequality, as are all earth-bound reactions. 
1. Ackerman, Diane. (1994). A Natural History of Love. Vintage Books.
2. Bennett, Frederick M. (1922). “Is Spirit a Chemical Reaction?”, The Personalist (pgs. 106-11), Vol. 3-4. School of Philosophy, University of Southern California.
3. (a) Thims, Libb. (2007). Human Chemistry (Volume One). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two). Morrisville, NC: LuLu.
4. Mishra, Prashant. (2010). “Chemistry of Love”, Pacial Chemist, blogspot.com, Nov. 06.
5. Safdar, Hina. (2010). “Drama Serial Chemistry: Subject of Love on Geo Tv”, Rewaj.com. Oct 17.
6. Chemistry of love (~Nostalgia89) – DeviantArt.com.
7. Chemistry (design) – GoodJoe.com.
● Young, Larry J. (2009). “Being Human: Love: Neuroscience Reveals All.” (abs) (overview) Nature, 457: 1079, Feb.
● Fisher, Maryanne and Costello, Victoria. (2010). The Complete Idiot’s Guide to The Chemistry of Love. Alpha.
● Kudashev, Dina. (date). “Chemistry of Love”, Asdn.net.