Chapter 10 Chemical bonding ii Nathan Warrachart

Molecular shape and polarity In diatomic molecules, if the bond is nonpolar, then the molecule as a whole is nonpolar In polyatomic molecules, polar bonds does not always result in a polar molecule, depending on the geometry If the dipole moments of individual polar bonds sum together to a net dipole moment, then the molecule will be polar Dipole moment= Difference in electronegativity If the dipole moments cancel our each other, (sum=0) then the molecule will be nonpolar

co2 Each C=O bond is polar because Oxygen and Carbon have significantly different electronegativities. However, CO2 is a linear molecule, so the polar ponds directly oppose one another and the dipole moment of one bond opposes the dipole moment of the other-cancelling each other out. Thus, the molecule is nonpolar Dipole moments cancel each other other because they are vector quantities: they have both a magnitude and a direction. Think of each polar bond as a vector pointing the the direction of the more electronegative atom and the length of the vector is proportional to the electronegativity difference.

h2o The O-H bonds are polar (3.5-2.1) However, H2O is bent, not linear. So the two dipole moments do not sum to zero If each bond is a vector pointing towards oxygen (most electronegative), the angle between the factors do not cancel.

Ch4 Opposite linear vectors cancel Net dipole moment=0

Common cases Linear= Nonpolar Bend= Polar Trigonal planar= Nonpolar Tetrahedral= Nonpolar Trigonal Pyramidal= Polar

Valence bond theory The valence electrons of the atoms in a molecule can reside in quantum mechanical atomic orbitals (s,p,d,f, or hybridizations) A chemical bond results from the overlap of two half-filled orbitals -The greater the overlap, the stronger the bond The geometry of the overlapping orbitals determines the type of the bond between atoms

Molecular orbital theory Wave function= A wavefunction is a function describing the probability of a particle's quantum state as a function of position Wave functions reinforced=Bonding molecular orbital (Bonds will form) δ^s Wave functions cancel= Anti bonding molecular orbital (Bonds won’t form)𝛿^* -When atoms get too close

Hybridization Hybridization- A mathematical procedure in which the standard atomic orbitals are combined to form new atomic orbitals called hybrid orbitals that correspond more closely to the actual distribution of electrons in chemically bonded atoms The total number of orbitals is conserved The combinations of standard atomic orbitals added together determines the shapes and energies of the hybrid orbitals formed The type of hybridization that occurs is the one that yields the lowest overall energy for the molecule

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