chem 102 yerkes university of illinois lecture
DESCRIPTION
Lecture from University of Illinois, Yerkes, Chemistry 102, Fall 2011, Freshman year classTRANSCRIPT
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Chemical Bonding
Why do bonds form? to lower the potential energybetween positive and negative charges
positive charges protonscations
negative charges electronsanions
metals
Periodic Tablelose e-
non-metalsgain e-
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Lewis electron-dot symbols
element symbol = nucleus + core e-
one “dot” = valence e-
metals dot = e- it loses to form cationnon-metal unpaired dot = e- paired through
e- gain or sharing
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metal + non-metal
Ionic bonding
Na (s)2 + Cl2 (g) NaCl (s)2
[Ne] [Ne] [Ne] [Ar]
Ca O: :..
..
[Ar]4s2[He]2s2 2p4
Ca2+ O2-
[Ar] [Ne]
Ca(s)2 2+ O2(g) CaO (s)
Na. + Cl-::
::+ Cl:
:: . Na+
3s1 3s23p5
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metal + non-metal
Ionic bonding
low Ionization Energy
lose 1 or 2 valence e-
high Electron Affinity
gain e-
electron transfer takes place
electrostatic attraction between cation and anion
formula = ratio of anions to cations
e-
+-
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Ionic sizes
isoelectronic series
46 e-
+49 +50 +51 ions get smaller
same # electrons
+-
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metal + non-metal
Ionic bonding
Na (s)2 + Cl2 (g) NaCl (s)2
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metal + non-metal
Ionic bonding
Na (s)2 + Cl2 (g) NaCl (s)2
exothermic heat given off
Ionization Energy Na + 496 kJ/mol
Electron Affinity Cl -349 kJ/mol
Lattice Energy
Na+
Cl-
E =d
-787 kJ/mol
Na++ Cl- NaCl
negative
Coulomb’s law
k Q1Q2
-640 kJ/mol
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Ionic solids
cation + anion+ -
metal non-metal
lithium oxygenLi O+ 2-
+Li O lithium oxide
magnesium nitrogen+
Mg N2+ 3- Mg N magnesium nitride3 2
strong interactions (ion-ion)
sodium chlorineNa Cl+ -
+NaCl sodium chloride
2
high melting points
801o C
> 1700oC
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Transition metals
more than 1 form except Ag+
Zn2+
Cd2+
Al3+
aluminum+sulfurAl3+ S2-
Al S2 3
aluminum sulfide
manganese oxygen+Mn1+ Mn2+ Mn3+ Mn4+
Mn4+ O2- MnO2
manganese(IV) oxide
Mn3+ Mn2O3
manganese(III) oxide
O2-
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+ non-metalnon-metal
Covalent bonding
electrons shared between atoms
high Ionization Energies
high Electron Affinities
electron density between the atoms
distance between atoms = bond length
formula = actual # atoms
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F.: ::
:F.:
:
+ .
: :F .:
:
F:
:
[He]2s22p5 [Ne]
F:
:: F:
::
e- not used in bonding lone pairs
Lewis structure
shared equally between F
H O.
::. .
:O:
. .H. H.
oxygen 2 lone pairsbonding pair
1s1 [He]2s22p4
[He]
shared e- bonding pair
not shared equally
[Ne]
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+ non-metalnon-metal
Covalent bonding
H. + H . H ..H1s1 1s1 [He]
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Covalent compounds
share valence electrons = chemical bondscarbon + chlorine
C Cl -4+
CCl4
carbon chloridetetra
1 mono2 di3 tri4 tetra5 penta6 hexa7 hepta8 octa
nitrogen + oxygenN O 2-?
NO nitrogen monoxide 2+
NO2 nitrogen dioxide 4+
N2O4 dinitrogen 4+
non-metal + non-metal
tetroxide
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Covalent compounds
H
N H1-3+ NH3 nitrogen trihydride ammonia
O2-1+ H2O dihydrogen monoxide water
weak forces low m.p. 0.0oC
Polyatomic ions
NH4+ ClO3
-
Table 2.5 p. 62
ammoniumOH- hydroxideNO3
- nitrateSO4
2- sulfatePO4
3- phosphate
chlorateMnO4
- permanganateCrO4
2- chromateCO3
2-carbonate
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metal + metalMetallic Bonding
metals valence e- well shielded
low Ionization Energy
low Electron Affinities
share valence e- not localized between atoms
delocalized
move freely throughout metal
Nae- “sea”
(nucleus and core e-)(valence e-)
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Electronegativity
ability of an atom in a moleculeto attract e- to itself
related to Ionization EnergyElectron Affinity
Pauling scale
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non-polar covalent 0.4polar covalent 0.5-1.8
NaCl 2.1 ionic 801oC
AlCl3 1.5 polar covalent 178oCPCl3 0.9 polar covalent 76oCCl2 0.0 covalent
ionic > 1.8
C HC O-+
Li2O
BeCl2 1.5 polar covalent 405oC Boiling/Melting points