Molecular Geometry

Molecules of different subtances have diverse shapes. Atoms attach to one another in various geometric arrangements. The overall molecular shape of a molecule is determined by its bond angles in three dimensions. The shape of a molecule is very important for its physical and chemical properties. Molekül geometrisini açıklamak için farklı kuramlar mevcuttur. modeller

VSEPR Valence Bond Theory

Molecular Orbital Theory

Valence Shell Electron Pair Repulsion

(VSEPR) Theory

It is a method for predicting the shape of a molecule from the

knowledge of the groups of electrons around a central atom.

Electron pairs (bonding and nonbonding electrons) repel one another, as a result , the electron pairs remain as far apart as possible from another as possible to minimize the repulsion.

• Two electron pairs in the valence orbital are arranged linearly • Three electron pairs are organized in a trigonal planar arrangement • Four electron pairs are organized in a tetrahedral arrangement • Five electron pairs are arranged in a trigonal bipyramid • Six electron pairs are organized in an octahedral arrangement

The repulsion of lone pair electrons is grater than the repulsion of bond pair electrons

Electron pairs assume orientations about an atom to minimize repulsions.

Applying the VSEPR theory.

• draw a plausible Lewis structure of the molecule or polyatomic ion.

• Determine the number of unshared electron pairs and numbers of bonds around the central atom ( multiple bonds count as a single bond)

• B + No• Establish the geometrical orientation of the electron pairs

around the central atom as linear, trigonal planar, tetrahedral,, trigonal bipyramid or octahedral

• Describe the molecular geometry

question: predict the shape of CO2 HCN CH4, NH3 SO2 PCl5,

SF6 and H2O by using VSEPR theory.

question: predict the shape of CO2 HCN CH4, NH3 SO2 PCl5,

SF6 and H2O by using VSEPR theory.

The nonbonding electron pairs are as important as bonding electron pairs in determining the structure.

Nonbonding electrons take up more space in the valence shell than the bonding electrons.

If one or more of the electron pairs are lone pairs, the distribution of electron pair and the geometrical shape of the molecule must be different.

The bond angles decrease as the number of nonbonding electron pairs increases

Repulsion strengths

lone pair -lone pair lone pair e-bond pair bond pair-bond pair

Valence bond theoryThe covalent bonds are formed by overlap of atomic orbitals each of which

contains one electron of opposite spin.

The valence bond method predicts molecule shapes from the shapes and orientation of the atomic orbitals and their overlap regions when two atoms approach.

In most cases the orbitals that overlap are reconfigured orbitals, called hybrid orbitals, having different shapes and orientations than pure orbitals.

The process of hybridization corresponds to a mathematical mixing of the valence-shell atomic orbitals.

Bonding in Methane

Valence Electron Pair Geometry

Number of Orbitals

Hybrid Orbitals

Linear 2 sp

Trigonal Planar 3 sp2

Tetrahedral 4 sp3

Trigonal Bipyramidal 5 sp3d

Octahedral 6 sp3d2

question : find the hybridazation type and geometry of CH4, PCl5, SF6. NH3 BeF2

Multiple Covalent Bonds

Molecular Orbital Theory

A molecular orbital describes a region of space in a molecule where electrons are most likely to be found.

Molecular orbitals are formed by combining atomic orbitals on different atoms.

Combining Atomic Orbitals

Bond Order = No. e- in bonding MOs - No. e- in antibonding MOs

2

Bonding in Metals

Electron sea model Band theory.

12-7 Bonding in Metals

• Electron sea model

Bonding in Metals

Band theory.

Band Theory

Semiconductors

Photovoltaic Cells