# Structural Biochemistry/Electronegativity
## Electronegativity

Electronegativity increases going up the periodic table and to the right of it. Meaning the most electronegative atom is Fluorine and the least electronegative atom is Cesium. What electronegativity means is the ability of an atom to attract electrons. For example, in a H-Cl bond, Cl is more electronegative than H. Therefore, the electrons will be closer to Cl.
Besides, because the nucleus of a smaller atom is closer to the shared pair than that of a larger atom, it attracts the bonding electrons more strongly. The electronegativity is inversely related to atomic size. In generaly, the nonmetals are more electronegativity than the metals. One of the important uses of electronegativity is determining the oxidation number of an atom. The atom's electronegativity refers to its ability to pull bonded electrons towards it. The greater the change in the electronegativity for the two atoms in a bond, the more polar the bond is and also the greater its ionic character.
Electronegativity is the ability of an atom in a molecule to attract a shared electron pair to itself, forming a polar covalent bond. The negative side of a polar covalent bond corresponds to the more electronegative element. In addition, the more polar a bond, the larger the difference in electronegativity of the two atoms.
There is no direct way of measuring electronegativity. Dipole-moment measurements tell us about the electrical behavior of all electron pairs in the molecule, not just the bonding pair in which we are interested. Also, the polarity of a bond depends on whether the bond is a single, double, or triple bond and on what the other atoms and electron pairs in a molecule are. Therefore, the dipole moment cannot tell us quantitatively the difference between the electronegativities of two bonded atoms.
Metals are the least electronegative of the elements.

## History

Electronegativity was first introduced by Pauling in the 1930s to describe bond energies. Pauling's calculations of electronegative from bond energies requires averaging over a number of compounds to cancel out experiemental errors. Jaffe used this idea to develop a theory of the electronegativity of orbitals rather than just atoms.
| Number | Symbol | Name | Electronegativity |
| 1 | H | hydrogen | 2.300 |
| 2 | He | helium | 4.160 |
| 3 | Li | lithium | 0.912 |
| 4 | Be | beryllium | 1.576 |
| 5 | B | boron | 2.051 |
| 6 | C | carbon | 2.544 |
| 7 | N | nitrogen | 3.066 |
| 8 | O | oxygen | 3.610 |
| 9 | F | fluorine | 4.193 |
| 10 | Ne | neon | 4.789 |
| 11 | Na | sodium | 0.869 |
| 12 | Mg | magnesium | 1.293 |
| 13 | Al | aluminium | 1.613 |
| 14 | Si | silicon | 1.916 |
| 15 | P | phosphorus | 2.253 |
| 16 | S | sulfur | 2.589 |
| 17 | Cl | chlorine | 2.869 |
| 18 | Ar | argon | 3.242 |
| 19 | K | potassium | 0.734 |
| 20 | Ca | calcium | 1.034 |
| 21 | Sc | scandium | 1.19 |
| 22 | Ti | titanium | 1.38 |
| 23 | V | vanadium | 1.53 |
| 24 | Cr | chromium | 1.65 |
| 25 | Mn | manganese | 1.75 |
| 26 | Fe | iron | 1.80 |
| 27 | Co | cobalt | 1.84 |
| 28 | Ni | nickel | 1.88 |
| 29 | Cu | copper | 1.85 |
| 30 | Zn | zinc | 1.59 |
| 31 | Ga | gallium | 1.756 |
| 32 | Ge | germanium | 1.994 |
| 33 | As | arsenic | 2.211 |
| 34 | Se | selenium | 2.434 |
| 35 | Br | bromine | 2.685 |
| 36 | Kr | krypton | 2.966 |
| 37 | Rb | rubidium | 0.706 |
| 38 | Sr | strontium | 0.963 |
| 39 | Y | yttrium | 1.12 |
| 40 | Zr | zirconium | 1.32 |
| 41 | Nb | niobium | 1.41 |
| 42 | Mo | molybdenum | 1.47 |
| 43 | Tc | technetium | 1.51 |
| 44 | Ru | ruthenium | 1.54 |
| 45 | Rh | rhodium | 1.56 |
| 46 | Pd | palladium | 1.59 |
| 47 | Ag | silver | 1.87 |
| 48 | Cd | cadmium | 1.52 |
| 49 | In | indium | 1.656 |
| 50 | Sn | tin | 1.824 |
| 51 | Sb | antimony | 1.984 |
| 52 | Te | tellurium | 2.158 |
| 53 | I | iodine | 2.359 |
| 54 | Xe | xenon | 2.582 |
| 55 | Cs | caesium | 0.659 |
| 56 | Ba | barium | 0.881 |
| 71 | Lu | lutetium | 1.09 |
| 72 | Hf | hafnium | 1.16 |
| 73 | Ta | tantalum | 1.34 |
| 74 | W | tungsten | 1.47 |
| 75 | Re | rhenium | 1.60 |
| 76 | Os | osmium | 1.65 |
| 77 | Ir | iridium | 1.68 |
| 78 | Pt | platinum | 1.72 |
| 79 | Au | gold | 1.92 |
| 80 | Hg | mercury | 1.76 |
| 81 | Tl | thallium | 1.789 |
| 82 | Pb | lead | 1.854 |
| 83 | Bi | bismuth | 2.01 |
| 84 | Po | polonium | 2.19 |
| 85 | At | astatine | 2.39 |
| 86 | Rn | radon | 2.60 |
| 87 | Fr | francium | 0.67 |
| 88 | Ra | radium | 0.89 |

## References

Miessler, Gary. Inorganic Chemistry. 4th Edition.