Polar Covalent Bonds Acids and Bases

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molecules

Slide 39

39

Dispersion Forces

• Occur between all neighboring molecules and arise because the electron distribution within molecules that are constantly changing

Slide 40

40

Hydrogen Bond Forces

• Most important noncovalent interaction in biological molecules

• Forces are result of attractive interaction between a hydrogen bonded to an electronegative O or N atom and an unshared electron pair on another O or N atom

Slide 41

41

Slide 42

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Summary

Organic molecules often have polar covalent bonds as a result of unsymmetrical electron sharing caused by differences in the electronegativity of atoms

The polarity of a molecule is measured by its dipole moment, .

(+) and () indicate formal charges on atoms in molecules to keep track of valence electrons around an atom

Some substances must be shown as a resonance hybrid of two or more resonance forms that differ by the location of electrons.

A Brønsted(–Lowry) acid donates a proton

A Brønsted(–Lowry) base accepts a proton

The strength Brønsted acid is related to the -1 times the logarith of the acidity constant, pKa. Weaker acids have higher pKa’s

Slide 43

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Summary (cont’d)

A Lewis acid has an empty orbital that can accept an electron pair

A Lewis base can donate an unshared electron pair

In condensed structures C-C and C-H are implied

Skeletal structures show bonds and not C or H (C is shown as a junction of two lines) – other atoms are shown

Molecular models are useful for representing structures for study

Noncovalent interactions have several types: dipole-dipole, dispersion, and hydrogen bond forces