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-
metal + non-metal
Ionic bonding
Groups 1 and 2 Groups 6 and 7
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-
+-
+ 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
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-)
metal + non-metal
Ionic bonding
http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA0/Movies/NACL1.html
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
-504 kJ/mol
Na++ Cl- NaCl
negative
Coulomb’s law
k Q1Q2
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
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)
Sn, Pb, Bi and Tl exceptions
Na. + Cl-::
::+ Cl:
:: . Na+
3s1 3s23p5
Ionic sizes
isoelectronic series
46 e-
+49 +50 +51 ions get smaller
same # electrons
+-
e-
+ non-metalnon-metal
Covalent bonding
H. + H . H ..H1s1 1s1 [He]
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]
Electronegativity
ability of an atom in a moleculeto attract e- to itself
related to Ionization EnergyElectron Affinity
Pauling scale
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