Electronegativity Is Like an Atomic Tug-of-War

"Electronegativity is the measure of an atom's affinity for electrons, and it is an intrinsic characteristic of each atom," says Eric Ferreira, associate professor in the department of chemistry at the University of Georgia. "It's based on numerous factors specific to the atom, including size and the number of protons in the nucleus."

The electronegativity of an atom is essentially a measurement of the relative likelihood that the shared electrons will be found closer to that atom than another.

"It works sort of like two individuals playing tug-of-war with a rope," says Ferreira. "The individuals are the atomic nuclei, and the rope is the electrons. If the individuals are pulling at equal strength, then the rope is equally shared. But if one individual is pulling harder than the other, then more of the rope will start collecting at the person pulling harder. Essentially, the person who is pulling harder is more electronegative, pulling rope (or electron) density toward it."

You'll remember from high school chemistry class, the protons in an atom's nucleus are positively charged, therefore attracting negatively charged electrons to orbit around them. When two atoms are bonded together, one way they stick together is by sharing a pair of electrons between them — this is called covalent bonding. But the atoms in a covalent bond may not share custody of the electrons equally — if atoms of two different elements are sharing electrons in a covalent bond, the electrons might spend more time closer to one atom's nucleus than the other. A good example of this is in the bond formed between one oxygen atom and two hydrogen atoms in a water molecule: The oxygen atom's nucleus attracts the shared electrons more strongly than the hydrogens' nuclei. Therefore, the oxygen atom is more electronegative than the hydrogens' — it's better than the hydrogens at attracting the electrons to its nucleus.

A good example of a way in which humans take advantage of electronegativity everyday is Teflon, the polymer polytetrafluoroethylene (PTFE), which can coat a pan to keep your scrambled eggs from sticking to it. This polymer is a long chain of carbon-on-carbon bonds, where each internal carbon atom also has two fluorine atoms bonded to it. Of all the elements, fluorine is the most electronegative, so the bonding electrons are being held tightly to the fluorine atoms.

Molecules can be attracted to each other through special interactions, like London dispersion forces. These forces are created when the constantly moving electrons in a molecule are pulled to one area of the molecule, creating spots in the molecule that are more negatively charged and others that are more positively charged.

In the specific case of Teflon, because fluorine is so electronegative, the nuclei in its atoms minimize the amount of electron movement — the fluorine atom is so attractive to the electrons that they rarely want to hang out around the carbon nuclei at all. This means the electron motion that would create attractive London dispersion forces is nullified, which results in the "nonstick" characteristics of Teflon.

Electronegativity also plays into the creation of pharmaceuticals:

"Many drugs are small molecules, and they are designed to interact with certain proteins in the body that have specific functions," says Ferreira. "These interactions are based on the physical shape of the molecule to precisely fit in the protein's receptor shape — think of a key fitting into a lock. These intermolecular interactions can be based on electrostatic forces, and therefore one could design drugs where the electronic nature is "tuned" at specific atoms based on their electronegativity to maximize the efficacy of the interaction."

So, next time you drink a glass of water or make a grilled cheese sandwich or take your medicine, thank chemistry for making every element a little bit different — and some more attractive than others.