intra- vs. inter-molecular forces
TRANSCRIPT
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Intra- vs. Inter-molecular Forces
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Intermolecular Forces
Networks Ionic Metallic Covalent
Molecules London Dispersion Dipolar (Dipole-Dipole) Hydrogen Bonding
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Network Forces
Sea of electrons around cations
Lattice of anions and cations
Localized, shared electrons
METALLIC
IONIC
NETWORK COVALENT
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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
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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.
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Dislikes do not mix
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Ion-Dipole Forces:
Highly polar solvents can dissolve ionic compounds.
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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
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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)
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Acid-Base
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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)
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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:
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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)