General and Inorganic Chemistry I.Lecture 5

István Szalai

Eötvös University

Outline

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Lewis Formulas and the Octet Rule

In most of their compounds, the representative elements (s andp �eld) achieve noble gas con�gurations.

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Lewis Formulas and the Octet Rule

In most of their compounds, the representative elements (s andp �eld) achieve noble gas con�gurations.

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Lewis Formulas and the Octet Rule

In most of their compounds, the representative elements (s andp �eld) achieve noble gas con�gurations.

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Resonance and Delocalization

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Dative Bond

[Fe(CN)]4−6

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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 lessthan eight valence shell electrons. bigskip

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Limitations of the Octet Rule

Compounds in which the central element needs a share in morethan eight valence 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 176C=C 134 611O=O 121 498C≡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 positivelycharged metal ions and mobile, delocalized electrons belongingto 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 valenceshell electrons on a central atom is signi�cant. The sets ofvalence shell electrons on the central atom repel one another.They are arranged about the central atom so that repulsionsamong them are as small as possible. Lone pairs of electronsoccupy 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

AX2 BeCl2, CdI2, HgBr2 linear

AX3 BF3,BF3, NO−3 trigonal planar

AX2E SO2, NO−2 angular

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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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VSEPR Theory

AX4 CH4, CCl4, NH+4 tetrahedral

AX3E NH3, SO2−3 trigonal pyramidal

AX2E2 H2O 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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AX5 PF5, SbCl5 trigonal bipyramidal

AX4E SF4 seesaw

AX3E2 ClF3 T-shaped

AX2E3 XeF2, I−3 linear

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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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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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AX6 SF6, SeF6 octahedral

AX5E BrF5 square pyramidal

AX4E2 XeF4 square planar

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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 pairsharing that results from the overlap of orbitals from two atoms.Usually, ”pure atomic” orbitals do not have the correct energiesand orientations to describe the where the electrons are whenan atom is bounded to other atoms. When other atoms arenearby as in a molecule, an atom can combine its valence shellorbitals (hybridization) to form a new set of orbitals (hybridorbitals).

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Valence Bond (VB) Theory

Linear GeometryBeCl2: Be [He] 2s2 Cl [Ne] 3s2 3p5Be 2s2 −−−−−→

hybridizesp

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Valence Bond (VB) Theory

Trigonal Planar GeometryBF3: B [He] 2s2 2p1 F [He] 2s2 2p5B 2s2 2p1 −−−−−→

hybridizesp2

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Valence Bond (VB) Theory

Tetrahedral GeometryCH4: C [He] 2s2 2p2 H 1s1C 2s2 2p2 −−−−−→

hybridizesp3

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Valence Bond (VB) Theory

Trigonal Pyramidal GeometryH3: N [He] 2s2 2p3 H 1s1N 2s2 2p3 −−−−−→

hybridizesp3

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Valence Bond (VB) Theory

Angular GeometryH2O: O [He] 2s2 2p4 H 1s1O 2s2 2p4 −−−−−→

hybridizesp3

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Valence Bond (VB) Theory

Trigonal Bipyramidal GeometryPF5: P [Ne] 3s2 3p3 F [He] 2s2 2p5P 3s2 3p3 −−−−−→

hybridizesp3d

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Valence Bond (VB) Theory

Octahedral GeometrySF6: S [Ne] 3s2 3p4 F [He] 2s2 2p5S 3s2 3p4 −−−−−→

hybridizesp3d2

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Valence Bond (VB) Theory

Double BoundsA double consists of one sigma and one pi bond. A sigma bondresulting from head-on overlap of atomic orbitals. A pi bondresulting from side-on overlap 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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