Section 8.2Section 8.2

The Nature of Covalent BondingThe Nature of Covalent Bonding

The Octet RuleThe Octet RuleAtoms share electrons so they have a Atoms share electrons so they have a

filled valence shell.filled valence shell.Most want 8 electrons in the outer shell-Most want 8 electrons in the outer shell-

like the noble gases. like the noble gases. Hydrogen and Helium are exceptions!Hydrogen and Helium are exceptions!

Who is likely to form covalent Who is likely to form covalent bonds?bonds?

Non-metallic atoms in Groups 4A, 5A, 6A, Non-metallic atoms in Groups 4A, 5A, 6A, and 7A and 7A

Types of Covalent BondsTypes of Covalent BondsSingleSingleDoubleDoubleTripleTriple

Single Covalent BondsSingle Covalent BondsFormed when a pair of electrons (two total Formed when a pair of electrons (two total

electrons) are shared between atoms.electrons) are shared between atoms.Showed by two dots in an electron dot Showed by two dots in an electron dot

diagramdiagram

Showed by a dash in a structural diagramShowed by a dash in a structural diagram

Unshared electron pairsUnshared electron pairs Indicated by dotsIndicated by dotsAlso called lone pairs or non-bonding pairsAlso called lone pairs or non-bonding pairs

Double and Triple Covalent BondsDouble and Triple Covalent Bonds

A double bond is formed when two A double bond is formed when two electron pairs are shared between atoms.electron pairs are shared between atoms.

A triple bond is formed when three A triple bond is formed when three electron pairs are shared between atoms.electron pairs are shared between atoms.

Why do polyatomic ions have a Why do polyatomic ions have a charge?charge?

If the charge on a polyatomic ion is If the charge on a polyatomic ion is negative, there are extra electrons added negative, there are extra electrons added to the valence electrons:to the valence electrons:

ResonanceResonanceA way to envision bonding in certain A way to envision bonding in certain

molecules.molecules.A resonance structure: one that occurs A resonance structure: one that occurs

when it is possible to draw two or more when it is possible to draw two or more valid electron dot structures that have the valid electron dot structures that have the same number of electron pairs for a same number of electron pairs for a molecule or ion.molecule or ion.

Ozone: Example of ResonanceOzone: Example of Resonance

VSEPR TheoryVSEPR Theory Molecules are three dimensionalMolecules are three dimensional VESPR Theory accounts for thisVESPR Theory accounts for this Stands for:Stands for:

VValence alence SShell hell EElectron lectron PPair air RRepulsion epulsion

VSEPR ContinuedVSEPR ContinuedThis theory states that unshared electron This theory states that unshared electron

pairs push away from each other so they pairs push away from each other so they stay as far away from each other as stay as far away from each other as possible.possible.

The result: the bonds “bend” to form The result: the bonds “bend” to form angles with the central atom and give angles with the central atom and give molecules three-dimensional shapesmolecules three-dimensional shapes

# # atomsatoms

ShapeShape AngleAngle ExampleExample

22 Linear Linear diatomicdiatomic

180180ºº NN22

33 Linear Linear triatomictriatomic

180180ºº COCO22

33 Bent Bent triatomictriatomic

105105ºº HH22OO

44 Trigonal Trigonal PlanarPlanar

120120⁰⁰ AlClAlCl33

44 PyramidalPyramidal 107107ºº NHNH33

55 TetrahedralTetrahedral 109.5109.5ºº CHCH44