Chemistry Regents - Bonding Theories and Polar Bonds Notes

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Molecular Orbit

When two atoms combine, this model assumes that their atomic orbitals

overlap to produce molecular orbitals,

or orbitals that apply to the entire molecule

Just as an atomic orbital belongs to a

particular atom, a molecular orbital belongs to a molecule as a whole

A

molecular orbital that can be occupied by two electrons of a covalent bond is

called a bonding orbital.

VSEPR Theory

The

valence-shell electron-pair repulsion theory, or VSEPR theory, explains the three-dimensional shape of molecules.

According

to VSEPR theory, the repulsion between electron pairs causes molecular shapes

to adjust so that the valence-electron pairs stay as far apart as possible.

Molecular shapes:

Polar Bonds and Molecules

Bond Polarity

When the atoms in the bond pull equally, the

bonding electrons are shared equally, and the bond is a nonpolar covalent bond

A polar

covalent bond, know also as a polar

bond, is a covalent bond between atoms in which the electrons are shared

unequally

The more

electronegative atom attracts electrons more strongly and gains a slightly

negative charge. The less

electronegative atom has a slightly positive charge

0.0-0.4 --> nonpolar covalent

0.4-1.7 --> polar covalent

1.7 – 4 --> ionic

Polar Molecules

In a polar

molecule, one end of the molecule is slightly negative and the other end is

slightly positive

A molecule that has two poles is called a

dipolar molecule, or dipole

When

polar molecules are placed between oppositely charged plates, they tend to

become oriented with respect to the positive and negative plates

Attractions Between Molecules

Intermolecular

attractions are weaker than either ionic or covalent bonds

The two weakest attractions between molecules

are collectively called van der Waals

forces

Van der Waals forces consist of dipole

interactions and dispersion forces

Dipole

interactions occur when polar molecules are attracted to one another

Dispersion

forces - the weakest of all molecular interactions, are caused by the motion

of electrons

Hydrogen

bonds are attractive forces in which a hydrogen covalently bonded to a very

electronegative atom is also weakly bonded to an unshared electron pair of

another electronegative atom

Intermolecular Attractions and Molecular Properties

A solid in which all of the atoms are covalently

bonded to each other is called a network

solid.

Melting a

network solid would require breaking covalent bonds throughout the solid

Bonding Theories