General and Inorganic Chemistry I.Lecture 1
Istvan Szalai
Eotvos University
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Outline
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Lewis Formulas and the Octet Rule
In most of their compounds, the representative elements (s and p field)achieve noble gas configurations.
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Resonance and Delocalization
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Dative Bond
[Fe(CN)]4−6
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Limitations of the Octet Rule
Compounds in which the central element needs a share in less than eightvalence shell electrons. bigskip
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Limitations of the Octet Rule
Compounds in which the central element needs a share in more than eightvalence shell electrons.
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Limitations of the Octet Rule
Compounds or ions with odd number of electrons.
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Bond Order
single bond (σ bond [s − s, s − p, p − p])
double bound (1 σ bond + 1 π bond [p − p])
triple bound (1 σ bond + 2 π bonds)
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Bond Energy, Bond Length
bond length (pm) bond energy (kJ/mol)
H−H 74 436C−C 154 347N−N 140 159O−O 132 138F−F 128 159Si−Si 234 176
C=C 134 611O=O 121 498
C≡C 121 837N≡N 110 946
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Bond Polarity, Dipole Moments
~µ = Q · ~d
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Molecular Polarity
~µ = Q · ~d
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Metallic Bond
It results from the electrical attractions among positively charged metalions and mobile, delocalized electrons belonging to the crystal as a whole.
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Continuous Range of Bonding Types
∆EN = 0 apolar covalent or metallic bond0 < ∆EN < 2 polar covalent or metallic bond2 < ∆EN ionic bond
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VSEPR Theory
Valence shell electron pair repulsion theory: Each set of valence shellelectrons on a central atom is significant. The sets of valence shellelectrons on the central atom repel one another. They are arranged aboutthe central atom so that repulsions among them are as small as possible.Lone pairs of electrons occupy more space than bonding pairs.
A: central atom, X: shared electron pairs, E: lone (unshared) pairs
AXnEm
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VSEPR Theory
AX2 BeCl2, CdI2, HgBr2 linear
AX3 BF3,BF3, NO−3 trigonal planar
AX2E SO2, NO−2 angular
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VSEPR Theory
AX4 CH4, CCl4, NH+4 tetrahedral
AX3E NH3, SO2−3 trigonal pyramidal
AX2E2 H2O angular
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AX5 PF5, SbCl5 trigonal bipyramidal
AX4E SF4 seesaw
AX3E2 ClF3 T-shaped
AX2E3 XeF2, I−3 linear
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AX6 SF6, SeF6 octahedral
AX5E BrF5 square pyramidal
AX4E2 XeF4 square planar
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Valence Bond (VB) Theory
Valence bond theory describes covalent bonding as electron pair sharingthat results from the overlap of orbitals from two atoms. Usually, ”pureatomic” orbitals do not have the correct energies and orientations todescribe the where the electrons are when an atom is bounded to otheratoms. When other atoms are nearby as in a molecule, an atom cancombine its valence shell orbitals (hybridization) to form a new set oforbitals (hybrid orbitals).
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Valence Bond (VB) Theory
Linear GeometryBeCl2: Be [He] 2s2 Cl [Ne] 3s2 3p5
Be 2s2 −−−−−→hybridize
sp
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Valence Bond (VB) Theory
Trigonal Planar GeometryBF3: B [He] 2s2 2p1 F [He] 2s2 2p5
B 2s2 2p1 −−−−−→hybridize
sp2
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Valence Bond (VB) Theory
Tetrahedral GeometryCH4: C [He] 2s2 2p2 H 1s1
C 2s2 2p2 −−−−−→hybridize
sp3
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Valence Bond (VB) Theory
Trigonal Pyramidal GeometryH3: N [He] 2s2 2p3 H 1s1
N 2s2 2p3 −−−−−→hybridize
sp3
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Valence Bond (VB) Theory
Angular GeometryH2O: O [He] 2s2 2p4 H 1s1
O 2s2 2p4 −−−−−→hybridize
sp3
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Valence Bond (VB) Theory
Trigonal Bipyramidal GeometryPF5: P [Ne] 3s2 3p3 F [He] 2s2 2p5
P 3s2 3p3 −−−−−→hybridize
sp3d
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Valence Bond (VB) Theory
Octahedral GeometrySF6: S [Ne] 3s2 3p4 F [He] 2s2 2p5
S 3s2 3p4 −−−−−→hybridize
sp3d2
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Valence Bond (VB) Theory
Double BoundsA double consists of one sigma and one pi bond. A sigma bond resultingfrom head-on overlap of atomic orbitals. A pi bond resulting from side-onoverlap of atomic orbitals.C 2s2 2p2 −−−−−→
hybridizesp2
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Valence Bond (VB) Theory
Triple BoundsA triple bound consists of one sigma and two pi bonds.C 2s2 2p2 −−−−−→
hybridizesp
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