LECTURE 18- Nonpolar and Polar Covalent Bonds

nonpolar covalent (pure covalent bond)

atoms of the same element bond together

if two atoms sharing bond-pair of electrons are identical

• share bonding electrons equally

• pair of electrons occupy region of space that extends over both nuclei

• concentrates electron density at the center between 2 nuclei

polar covalent bond

bonding pair of electrons shared unequally

one atom has a stronger attraction for the electrons than the other

covalent bond between atoms of different electronegativities

electronegativity (x)

ability of an atom to attract bonding electrons to itself when it is covalently bonded to other atoms

bonding pair of electron is more attracted to atom with higher electronegativity

electrons occupy a region of space that extends over both nuclei but concentrates electron density closer to the atom with the higher electronegativity

electrostatic potential/ electron density map

darker colors mean higher magnitude

light blue/ pink

less polar

dark blue/ pink

more polar

knowing electronegativity can help determine

direction of polarity

difference between the electronegativity values (ΔX)

help us estimate unequal sharing of electrons in covalent bonds

as ΔX increases

bonds become more polar & polarity of the bond increases

polar covalent bond is intermediate in nature between

a nonpolar covalent bond and an ionic bond

dipole moment (u)

magnitude of the polarity of a polar covalent bond is measured

dipole depends on

• magnitude of partial charge

  • distance between the 2 charges

dipole equation

u = Ser

s

magnitude of partial charge

e

charge of electron (1.602 × 10^-19C, C is coulomb)

r

inter-nuclear distance (bond length in meters)

SI unit of u is coulomb meter (Cxm)

often given in units of debyes (D): 1D= 3.336 × 10^-30 Cxm

∆X= 0

nonpolar molecules

dipole moment increases as ∆X increases

other molecules

even small electronegativity differences between the bonded atoms in a long bond will result in

a significant bond dipole moment (I-Cl)