MOLECULES Part 4: BOND ORDER, LENGTH AND ENERGY
MOLECULAR SHAPE AND DIPOLE MOMENTS
^What to catch from above slide:
First and foremost, chemical bonding is driven by interaction between valence electrons
HCl is a covalent bond, but it is a polar covalent bond because the greater electronegativity in Chlorine hogs more electron density than the Hydrogen atom
Now, "electronegativity" = a measure of the tendency of an atom to attract a bonding pair of electrons towards itself
"electron density" = a representation of the probability of finding an electron in a specific location
The arrow we see represents the "dipole moment" = extent of charge displacement towards more electronegative atom
^More electron density around the Chlorine atom suggests that there is a HIGHER PROBABILITY you will find electrons near Chlorine than Hydrogen!
^Direction is important because the NET DIPOLE depends on the direction of two or more dipole moments within a given molecule: take a look at the below diagram (NET DIPOLE is represented by the BLUE ARROW)
^Again, the blue arrow represents the net dipole. Notice BCl3 has no blue arrow, because the dipole moments that are directed towards opposite directions have cancelled themselves out (NET DIPOLE = 0). Same is the case for "CCl4", "PF5", and "SF6".
POLAR bonds have a net dipole. NON-POLAR bonds don't have a net dipole
^What to catch from above slide:
When dipole moments face opposite directions (as seen in CO2 and CCl4), then they cancel out to give rise to net dipole of 0. Thus they become non-polar covalent bonds!
BOND ORDER, BOND LENGTH & BOND ENERGY
^ Single bond has bond order of 1, double bond a 2, and triple bond a 3.
^Bond length can be estimated with sum of covalent radii of two atoms as shown above
^Single bond has greatest bond length, then double bond, then triple bond as shown above
^What to catch from above slide:
BE = energy required to break one mole of covalent bonds
^What to catch from above slide:
Each type of bond has an experimentally determined value of Bond Energy in kJ/mol
The total BE can be determined by summing up all of the energies for various bonds
Generally, triple bond has greatest BE, then double bond, then single bond
^Bond Dissociation Energy (BDE) and BE are referring to the same thing. In this case, Cl2 has a bond energy of 59kcal/mol.
^We discussed that enthalpy of reaction can be ESTIMATED from BOND ENERGIES:
Do note that the enthalpy of reaction is determined by calculating BE of REACTANTS then subtracting BE of PRODUCTS from it.
^Try this on your own as practice.
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