Intermolecular Forces - Chapter 4 Review

Electronegativity

• Measure of how much a particular atom attracts electron pairs to itself in a Covalent Bond

• Increases along a period

• Decreases down a group

• (Highest) F > O > N > Cl > Br (Lowest)

Non-Polar

• Electronegativity between 2 covalently bonded atoms are the same

• Electron pair is equidistant from nucleus

Polar

• Electronegativity between 2 covalently bonded atoms is unequal

• The center of the negative charge does not overlap with the positive charge

• Electron distribution is asymmetric (Dipole)

• Polarity of bonds increases reactivity by allowing polar reagents to “attack” bonds. 

Van Der Waal/ Temporary Dipole-Induced Dipole/ London-Dispersion Forces

• Electron charge clouds in any molecule are random; it can have imbalanced clouds that cause one end of the particle to have a negative charge/ temporary dipole

• These temporary dipoles induce dipoles in other molecules

• Dipoles attract each other

Permanent Dipole-Dipole Forces

• Forces between polar molecules with permanent dipoles

• Stronger than Van Der Waal forces when comparing polar molecules to non-polar molecules with the same number of electrons

Hydrogen Bonding

• Strongest IMF 

• requires 1 molecule w/ a hydrogen covalently bonded to N, O, or F & 1 molecule w/ N, O, or F with a lone pair of electrons

• Hydrogen that is covalently bonded has a very high polarity that makes it positive, attracting it to lone pairs which are negatively charged.

Properties of Water 

• Higher Boiling point than other dihydrogen molecules due to Hydrogen Bonds

• High Viscosity and Surface Tension as Hydrogen Bonds apply a downward force

• Less dense as ice due to extended Hydrogen Bonds between water molecules