Intra- vs. Inter-molecular Forces

Intermolecular Forces

  Networks   Ionic   Metallic   Covalent

  Molecules   London Dispersion   Dipolar (Dipole-Dipole)   Hydrogen Bonding

Network Forces

Sea of electrons around cations

Lattice of anions and cations

Localized, shared electrons

METALLIC

IONIC

NETWORK COVALENT

Intermolecular Forces

  London Dispersion . . . 0.5 kJ mol-1 to 5 kJ mol-1   H-bonding . . . ~20 kJ mol-1   Covalent . . . ~150 kJ mol-1 to 1,000 kJ mol-1

Molecular shape and overall dipoles

Some molecules possess regions that are polar and regions that are non-polar.

Some molecules possess a single overall polar or non-polar nature.

Dislikes do not mix

Ion-Dipole Forces:

Highly polar solvents can dissolve ionic compounds.

Reactions in Aqueous Solution

  Several types of reactions occur in water, i.e. in aqueous solution   (aq) is the designation for aqueous

  Will involve ionic and / or highly polar species   Three common aqueous reaction types are:

  precipitation   acid-base   oxidation-reduction

Precipitation   An anion and a cation form an insoluble ionic compound

  ex. silver nitrate, AgNO3(aq), and salt, NaCl(aq), are mixed

  Ag+(aq) and Cl-(aq) combine

to yield AgCl(s)

AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s) Ag+

(aq) + Cl-(aq) → AgCl(s)

Acid-Base

Acid-Base   Hydrochloric acid, HCl, and sodium hydroxide,

NaOH, are mixed, react and form water:   HCl, an acid donates H+ ions (protons) and NaOH

acts as a base, furnishing OH- ions

HCl(aq) + NaOH(aq) → NaCl(aq)+ H2O(l) H+

(aq) + OH-(aq) → H2O(l)

Oxidation-Reduction (Redox)

  The items exchanged are electrons.   The species that loses electrons is said to be oxidized (and is called the reducing agent).   The species that gains electrons is said to be reduced (and is called the oxidizing agent).   An example of a redox reaction occurs between hydrochloric acid and zinc metal:

Oxidation-Reduction (Redox)

  Zn atoms lose electrons and are oxidized to form Zn2+ ions:

Zn(s) → Zn2+(aq) + 2e-

  H+ ions of the HCl gain electrons and are reduced to H atoms, which combine to form H2 molecules:

2H+(aq) + 2e- → H2(g)

  The overall equation for the reaction: Zn(s) + 2H+

(aq) → Zn2+(aq) + H2(g)