Electronegativity and Polarity
Elecronegativity
• Relative ability of an atom to attract electrons
in a chemical bond
• Fluorine has the highest electronegativity
value
• Trend:
– Increases across (left to right) a period
– Decreases down a group
Types of covalent bonds
–Non-polar covalent: equal sharing of
electrons
–Polar covalent: unequal sharing of
electrons
Non-polar covalent
• Sharing of electrons equally
• Usually occurs when two identical atoms
are bonded together.
• Examples: H2, O2, N2, Cl2, Br2, I2, F2
Polar covalent
• Unequal sharing of electrons
• Unequal sharing caused by 2 elements
with different electronegativities
(different abilities to attract electrons).
• The bond is called a dipole (two poles)
• Creates molecule with partial charges
• Partial charges symbolized by (delta)
+ and • The more electronegative atom is located
at the partially negative end
• Example:
+ H-Cl and
H-Cl
Polar molecule or not?
• The shape of a molecule usually tells if a
molecule is polar or not
• If the VSEPR shape is symmetric it is
usually non-polar
• If the molecule is asymmetric it is polar
Name
Linear
Polar
example
HCl
Non-polar
example
CO2
Trigonal Planar
CH2O
AlH3
Tetrahedral
CH3OH
CH4
Trigonal pyramidal
always
Bent
always
Youtube polar vs nonpolar
Intermolecular Forces
• The force that exists between separate
molecules.
• This force attracts molecules to each other.
• 3 Types
– London Dispersion force or induced dipole moment
between molecules; only force in non-polar
molecules; weakest force (caused by the motion of
electrons) (ex: CH4)
Induced dipole moment
– Dipole-dipole the force between two polar
molecules; stronger force (ex: HCl)
– Hydrogen bond forms between the hydrogen end of one
dipole and fluorine, oxygen, or nitrogen (that have at
least one lone pair) end of another dipole; strongest
force (ex: H2O)
Hydrogen bond
IMF’s
• ALL molecules have dispersion forces
• All polar molecules have dipole-dipole forces
and dispersion forces
• Molecules that hydrogen bond have all 3
Solubility of polar molecules
• Properties are due to intermolecular forces
• Like dissolves like
– Polar substances will dissolve polar molecules
(and ionic compounds)
– Non-polar substances will dissolve non-polar
molecules