Grade 12 Chem Noncovalent Intermolecular Forces London Forces Dipole-Dipole Attraction Hydrogen Bond

Noncovalent Intermolecular Forces
Liquid and solid are condensed states of matter
Since a liquid or solid has particles that are closer together, its physical properties are influenced by noncovalent intermolecular forces (strong interactions between particles)
Polar v. Nonpolar:
A particle or molecule is nonpolar when the difference in electronegativity (tendency to attract electrons) values is less than 0.5 or when the shape and distribution of electrons are symmetrical
A particle or molecule is polar when the difference in electronegativity (tendency to attract electrons) values is at least 0.5 and the shape and distribution of electrons are not symmetrical
London Forces:
Developed when a temporary dipole in one molecule induces temporary dipoles in adjacent molecules
Present between molecules of ALL molecular substances
Also present between atoms of noble gases
The only noncovalent intermolecular force present in nonpolar molecules
Weakest among the three types of noncovalent intermolecular force
The more electrons a particle has, the stronger the London forces
Dipole-Dipole Force:
Due to attraction between oppositely charged ends of permanent dipoles
Present between polar molecules in addition to London forces
Stronger than London forces
The more polar the particle is, the stronger the dipole-dipole force
Hydrogen Bonding:
Attractive force exerted by H atom in X - H on lone electron pair in Z where X, Z: F, O, or N
Strongest among the three types of noncovalent intermolecular force
Summary:
Nonpolar molecules have London forces only
Polar molecules have London forces and dipole-dipole force
Polar molecules with H bonded to F, O, or N have London forces, dipole-dipole force, and hydrogen bond
The strength of noncovalent intermolecular forces influences the physical properties of liquids and solids
Strong noncovalent intermolecular forces cause higher boiling point and higher melting point
The substance with the strongest noncovalent intermolecular forces (most number of hydrogen bonds) has the highest boiling point