Chemistry Regents - Bonding Theories and Polar Bonds Notes

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 covalent1.7 – 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