CHEM1112 Lecture Notes - Lecture 10: Chemical Polarity, Covalent Bond, Partial Charge
17 May 2018
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Electronegativity
• Ability to attract electrons to the bond it makes towards itself
• Place in periodic table: increases across the period, up a group
• Covalent and polar covalent bonds: when 2 atoms are identical- in covalent bond, pull =
identical, equally shared electrons. Different atoms- electrons pulled towards more
electronegative atom, creating a negative partial charge (delta-) and positive partial charge
(delta+)
• Pure covalent bond: each atom contributes 1 electron , equally shared. Partial charge on an
atom= 1-2 x1/2=0
• Polar covalent bond: fraction of electron pair depends on atom electronegativity.
• Estimating partial charges: electronegativity for H and Cl are 2.20 and 3.16 : partial charge on
H= 1-2 * 2.20/(2.20+3.16)=0.1791. Partial charge on Cl= 1-2* 3.16/(2.20+3.16)=-0.1791
•
• Different atoms: if electronegativities are very different, electrons pulled completely to
electronegative one, ie: ionic bonds-NaCl= full negative charge and full positive charge.
• Difference in electronegativity = d. if 0<d<0.4= pure covalent bond
• If 0.4<d<2.0= polar covalent bond
• If d>2.0= ionic bonding
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