Bonding II

Bonding I – you learned..

Classifying Bonds Calculate the Lattice Energy of Ionic Compounds Write Lewis Structures Formal Charges Drawing Resonance Structures Exceptions to the Octet Rule

The incomplete octet Odd-electron molecules The expanded octet

Using Bond enthalpies to Estimate the Enthalpy of a Reaction

Bonding II – you will learn…

Molecular Geometry – VSEPR models Molecule in which the central atom has NO lone pairs Molecule in which the central atom has lone pairs Molecule in which there is more than one central atom

Predicting Dipole Moments Hybridization of Atomic Orbitals

Hybridization of s and p orbitals Hybridization of s, p and d orbitals Hybridization in molecules containing double and triple bonds.

Molecular Orbital Diagrams

Molecular Geometry - VSEPR models

VSEPR models - Accounts for electron pairs around atoms. Minimizes electron-pair repulsion.

Guidelines for Applying Draw the Lewis Structures Only consider electrons around the central atom

Account for both bonding and non-bonding (lone) pairs Treat double and triple bonds as single bonds, Ex: CO2 .. O=C=O.

Look at table 10.1 for overall arrangement of electrons. In predicting bond angles

Lone pairs repel lone pairs and shared pairs more strongly than bond pairs of electrons.

There is no accurate way to predict exact bond angles when the central atom possesses one or more lone pairs.

Molecular Geometry - atom has NO lone pairs

General formula ABx where A is the central atom, B is/are the surrounding atoms and x is a number between 2 and 6…… most of the time.

Table 10.1 shows five possible arrangements of electron pairs around the central atom A.

Table 10.1 shows number of electron pairs, arrangement and molecular geometry.

Predict the geometry of CO2, SnCl4 and NO3-1, PF5

Problems 10.8, 10.10, 10.12

Molecular Geometry – atom has lone pairs

General formula ABxEy where A is the central atom, B is/are the surrounding atoms, E is the number of lone pairs and x is a number between 2, 3.. and y 1,2,3, …...

Approach.. Count all electron pairs on the central atom The number of electron pairs around the central atom determines the electron

arrangement around the central atom HOWEVER, the molecular geometry will NOT be the same as the electron

arrangement. Geometry is based on atoms alignment, leaving out the lone pairs.

Table 10.2 – lone pair configuration Class of molecule, i.e. ABxEy

# of electron pairs Number of bonding pairs Arrangement Number of lone pairs Molecular geometry.

Practice - Predict the geometry of O3, XeF2, IF5

Problems 10.14

Molecular Geometry - more than one

central atom

A Central Atom Bonded to two or more atoms

Many molecules have more than one central atom.

Solve by making each of the central atoms the central atom. Multi-step determination C2H8 and C2 H4 are examples

H4C-CH4

H2C=CH2

Predicting Dipole Moments

Two factors determine the if a molecule has a dipole moment.

Are the bonds in the molecule polar? Electron negativity determine if the bonds are polar. Shift in electron density is symbolized by

Is the molecule polar? Bond moment is a vector quantity and magnitude and direction. Vector is the sum of the bond moment. Check out the following; CO2 CCl4, CCl2H2

Problems 10.20, 10.22, 10.24

Valence Bond Theory (VB)

Introduced to explain chemical bond formation. Describes covalent bonding as overlapping atomic orbitals Orbitals share common regions of space. VB uses the concept of hybridization

Blending/combining of two or more non-equal atomic orbits such as s and p to make a new hybrid sp orbit.

Hybrid orbitals overlap to create a covalent bond. Hybrid orbitals allow paired electrons to become unpaired for bonding

Unpaired valence electrons do the bonding.

Steps for determining type of hybrid orbitals Draw Lewis structures Use VSPRE to determine electron pair arrangement (Table 10.1, 10.2) Use Table 10.4 to determine hybrid state of central atom.

Valence Bond Theory – sp hybridization

sp hybrid orbit Combines the s orbital and one p-orbital to form two equal obitals called sp-

orbital, i.e. BeCl2 Linear

sp2 hybrid orbit Combines the s orbital and two p-orbital to form two equal obitals called sp-

orbital, i.e. BCl3 Trigonal planar – 120o angles

sp3 hybrid orbit Combines the s orbital and three p-orbital to form two equal obitals called

sp-orbital, i.e. CH4

Tetrahedron – 109.5o

Problems 10.32, 10.34, 10.36

Valence Bond Theory – sp hybridization

sp3d hybrid orbit 5 equivalent hybrid orbitals Trigonal bipyramid, 120o, 90o

sp3d2 hybrid orbit 6 equivalent hybrid orbitals octahedral, 90o

Hybrid double and triple bonds

Determine the bonds that overlap with double and triple bonds

Two types of bonds Sigma σ bond – end-to-end overlap Pi bonds – side-to-side overlap