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Covalent Bonding

Covalent Bonding. Sec. 8.4: Molecular shape. Objectives. Discuss the VSEPR bonding theory Predict the shape of and the bond angles in a molecule Define hybridization. VSEPR Model. Molecular shape determines many physical and chemical properties of compounds

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Covalent Bonding

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  1. Covalent Bonding Sec. 8.4: Molecular shape

  2. Objectives • Discuss the VSEPR bonding theory • Predict the shape of and the bond angles in a molecule • Define hybridization

  3. VSEPR Model • Molecular shape determines many physical and chemical properties of compounds • The ValenceShell Electron Pair Repulsion model is used to determine molecular geometry (shape).

  4. VSEPR Model • Molecular shape is determined by the overlap of orbitals that are sharing electrons • Atoms/orbitals assume a shape that minimizes the repulsion of shared and unshared pairs of electrons around the central atom.

  5. VSEPR Model • Shared pairs (covalent bonds) repel one another • Lone pairs also repel one another • In addition, lone pairs repel shared pairs and push shared pairs closer to each other (because of the relatively large orbitals of the lone pairs) • Consider an analogy ...

  6. VSEPR Model • Repulsions of electron pairs for each other results in atoms being at fixed angles to each other. • The angle formed by 2 terminal atoms and the central atom is a bond angle. • Table 6 (pg. 263) summarizes molecular shapes and angles predicted by the VSEPR theory.

  7. Molecular shape: Linear • No lone pairs present on central atom. • 2 bonding pairs present • Maximum separation is attained at a bond angle of 1800 Ex. BeCl2

  8. Molecular shape: Linear • The shape for a central atom with double or triple bonds is linear. These types of bonds are rigid and hold the atoms involved in a linear configuration.

  9. Trigonal Planar • No lone pairs present on central atom. • 3 bonding pairs present. • Maximum separation is attained at bond angles of 1200 Ex. AlCl3

  10. Tetrahedral • No lone pairs present on central atom. • 4 bonding pairs present. • Maximum separation is attained at bond angles of 109.50 Ex. CH4

  11. Trigonal Pyramidal • 1 lone pair present on central atom • 3 bonding pairs present • Lone pair takes up more space than a bonding pair • Bonding pairs are pushed closer together • Bond angles are 107.30

  12. Bent • 2 lone pairs present • 2 bonding pairs present • Lone pairs take up more space than bonding pairs • Bond angles are 104.50

  13. Trigonal Bipyramidal • No lone pairs present • 5 bonding pairs present • Bond angles are 900 vertical to horizontal • Bond angles are 1200 horizontal to horizontal

  14. Octahedral • No Lone pairs present • 6 bonding pairs present • Bond angles are 900

  15. Hybridization • When 2 of the same type of object combine, a hybrid results that has characteristics of both objects. • During bonding, orbitals undergo hybridization. • Hybridization is a process in which atomic orbitals are mixed to form new, identical hybrid orbitals.

  16. CH4 (methane) • Carbon has 4 valence electrons: [He] 2s2 2p2 • The electrons in the s orbital unpair: [He] 2s1 2p3 • Hybrid orbitals - formed in bonding from the 1 “s” and 3 “p” orbitals - are called sp3

  17. Hybridization • Like the carbon in methane, hybridization of orbitals occurs in all covalent compounds. • Depending on exactly which orbitals hybridize, the “name” of the hybridization can vary. Recall it is called “sp3” for methane. • The 5th column of the table on pg. 263 gives the names of the hybridizations associated with each shape.

  18. Practice Problems • Determine the shape, bond angles, and hybridization of • PH3 • BF3 • NH4+ • OCl2 • KrF2

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