Chapter VII

7.1. Types of bonding

7.2. Lewis structures, the octet rule Lewis Structure: Representation of a molecule that shows how the valence electrons are arranged among the atoms in the molecule. Bonding involves the valence electrons of atoms. Example: Na●

Lewis structures of elements Dots around elemental symbol Symbolize valence electrons Thus, one must know valence electron configuration

Rules for Lewis structures of molecules Write out valence electrons for each atom Connect lone electrons because lone electrons are destabilizing Become two shared electrons Called a “bond” Check to see if octet rule is satisfied Recall electron configuration resembling noble gas In other words, there must be 8 electrons (bonded or non-bonded) around atom Non-bonded electron-pair Called “lone pair”

Let’s do some examples on the board Duet rule H2 Octet rule F2 O2 N2

Lewis structures Example Write the Lewis Structure for the following molecules: H2O CCl4 PH3 H2Se C2H6

Lewis structures continued C2H4 C2H2 SiO2

7.3. Valence shell expansion and deficiency A hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements formally bearing more than eight electrons in their valence shells.

Let us apply the rules to this case: Step 1: . Example 1 6 Let us apply the rules to this case: Step 1: Total valence electrons = 6 + 6 7 = 48 Step 2: Total electrons needed for octets = 7 8 = 56 Step 3: Total shared/bonding electrons = 56 - 48 = 8.

For the next example, consider the ion ClO Now, if we follow the rules of Lewis structures, we would obtain Step 1: Number of valence electrons  . Step 2: Number of electrons for octets  . Step 3: Number of shared electrons  .

7.4. Resonance structure Inchemistry, resonance or mesomerism  is a quantum superposition of wave functions built from Lewis structures as a way of describing delocalized electrons within certain molecules or polyatomic ions. A molecule or ion with such delocalized electrons is represented by several contributing structures  (also called resonance structures or canonical forms).

7.5. Formal charge calculations

7.5. Molecular geometry and hybridization All theory for explaining bonding Valence bond theory Valence Shell Electron Pair Repulsion Theory Theory and Orbital Hybridization Molecular Orbital (MO) Theory

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Table 11.1 Composition and Orientation of Hybrid Orbitals.

7.5. Molecular geometry and hybridization

7.6. Polarity of molecules