Polar Bonds and Molecules

Bond Polarity  Not all covalent bonds are equal in their sharing of electrons  A lot depends on the type of atoms involved and the number of them in the molecule  Bonding pairs are pulled between the two atoms When they are being pulled equally, the bond is nonpolar

Example of a Non-Polar Bond

Polar Bonds  Exist when there is an unequal sharing of electrons between atoms  Electronegativity is used to determine which atom exerts a greater pull on the electrons being shared  The more electronegative atom becomes slightly negative and the other atom becomes slightly positive

Different ways to express polarity within a molecule

Differences in Electronegativity  When determining polarity, compare electronegativities  When the difference between the two is: 0.0 – 0.4nonpolar covalent(H-H) 0.5 – 1.0moderately polar covalent (H-Cl) 1.1 – 2.0very polar covalent (H-F) >2.1ionic (NaCl)

Polar Molecules  If a bond is polar within a molecule, the entire molecule may be polar  One end of the molecule is slightly negative and the other end slightly positive  Molecules will orient themselves to be against an oppositely charged plate that comes into contact with them  It is possible for polar bonds to cancel each other out to become nonpolar

Intermolecular Forces  Weaker than ionic or molecular bonds 1. Van der Waals forces - There are two types a. Dipole interactions occur when polar molecules are attracted to one another b. Dispersion forces are caused by the movement of e-; occur between nonpolar molecules as well

Intermolecular Forces (cont’d) 2. Hydrogen bonding - When hydrogen bonds to a highly electronegative atom and also becomes attracted to an unshared pair of another electronegative atom - May be in the same molecule or another one entirely - They are the strongest of the intermolecular forces

Characteristics of Molecules  Can be solids, liquids or gases  Low melting and boiling points compared to ionic compounds  Solids form a network crystal (sugar) Ex. Diamond  Can either have high or low solubility  Poor conductors of heat and electricity