Chem11 U8 - Molecular Polarity, Intermolecular Forces (F, G)

polar bonds make what kinds of molecules?

polar molecule OR non polar molecule

- having polar covalent bonds do not automatically make the overall molecule polar

- non-polar molecules usually have symmetrical shapes

what kind of molecule does a non-polar bond make?

non-polar molecule (regardless of the shape); non-polar covalent bonds can only make non-polar molecules

polar molecules

have asymmetrical shapes

- Linear w/ 2 diff atoms

- Angular

- Trigonal pyramidal

non-polar molecules where dipoles cancel out

-Linear w/ 3 atoms

- Trigonal planar

- Tetrahedral

- Trigonal bipyramidal

- Octahedral

Van der Waals forces

intermolecular forces of attraction btwn molecules due to their positive & negative dipoles

London (dispersion) Forces

arise when momentary or temporary dipoles occur due to uneven distribution of electrons in any 1 second

-attraction btwn all atoms & molecules (eg. polar & non-polar molecules)

- strength increases as molar mass increases (more electrons)

- very weak (1/10 of dipole strength)

--> eg. I₂

Dipole-Dipole Forces

describe the attraction btwn molecules that have permanent dipoles

- attraction btwn polar molecules

- positive end attracted to negative end (& vice versa)

- weak attraction

--> eg. HCl

Hydrogen Bonds

are a special type of dipole-dipole forces that occurs btwn molecules w/ H bonded to a nitrogen, oxygen, or fluorine

- (N, O, & F are very electronegative elements w/ a small radius)

- stronger than most dipole-dipole interactions

- not chemical bonding

--> eg. H₂O

when is zero attraction possible?

only with ideal gases

intermolecular forces

forces between molecules

intramolecular forces

forces within molecules (bonds btwn atoms/ions)

forces from weakest to strongest?

INTERMOLECULAR (weak-moderate)

London force

Dipole-dipole

H-bonding

*Ion-dipole (ion w/ polar molecule) (overlaps a little w/ dipole-dipole, fully w/H-bonding, & a bit beyond)

INTRAMOLECULAR (strong-very strong)

Covalent bonds (overlaps w/ion-ion)

Ion-ion