Bonding and Chemical Interactions

MCAT Prep: General Chemistry Part 2

Octet rule

• an atom will bond until it has a full outermost shell

• an atom wants to have a configuration similar to that of Group VIII (noble gases)

Expectations

some elements are stable with fewer than 8 electrons. Atoms found in or beyond the third period can have more than eight valence electrons because some of the valence electrons may occupy d-orbitals. These atoms can have more than four bonds in Lewis structures.

H, He, Li

What elements only need 2 electrons to be stable?

Be

What element only need 4 electrons to be stable?

B

What element only need 6 electrons to be stable?

Lewis structure

the chemical symbol of an element surrounded by dots, each representing one of the s or p valence electrons of the atom

Formal charge

the charge an atom would have if all the electrons in bonds were shared equally

Polar covalent bond

bonding electron pair is not shared equally, but pulled toward more electronegative atom

Polarity of molecules

depends on the polarity of the constituent bonds and on the shape of the molecule

always nonpolar

a molecule with nonpolar bonds

polar or nonpolar

a molecule with polar bonds

shape

The overall ________ of the molecule determines whether the molecule is in fact polar or not

Linear

Regions of electron density: 2

Angle between electron pairs: 180 degrees

Trigonal planar

Regions of electron density: 3

Angle between electron pairs: 120 degrees

Tetrahedral

Regions of electron density: 4

Angle between electron pairs: 109.5 degrees

Trigonal bipyramidal

Regions of electron density: 5

Angle between electron pairs: 90, 120, and 180 degrees

Octahedral

Regions of electron density: 6

Angle between electron pairs: 90 and 180 degrees

Complex ion (coordination compound)

a Lewis acid-base adduct with a cation bonded to at least one electron pair donor (including water)

Ligands

donor molecules that use coordinate covalent bonds

Chelation

a process where the central cation can be bonded to the same ligand multiple times

Hydrogen bonding

the partial positive charge of the hydrogen atom interacts with the partial negative charge located on the electronegative atoms (F, O, N) of nearby molecules

Dipole-dipole interactions

polar molecules orient themselves such that the positive region of one molecule is close to the negative region of another molecule

Dispersion forces

the bonding electrons in covalent bonds may appear to be equally shared between two atoms, but at any particular point in time they will be located randomly throughout the orbital. This permits unequal sharing of electrons, causing transient polarization and counterpolarization of the electron clouds of neighboring molecules, inducing the formation of more dipoles