Bonding Day 3

Please answer the following on your own piece of paper Draw the Lewis structure for: CaI2 OCl2 Indicate whether the compounds in number 1 are ionic or covalent and describe what is happening with the electrons in the compounds (who is giving, who is taking and who is sharing).

Bond Strength and Length Strength, in general: Triple bonds are stronger than double which are stronger than single. See Table 16.3 on page 448 Usually listed in kJ/mol Example C2H2 Length, in general: Triple bonds are shorter than double which are shorter than single.

Resonance Structures which occur when two or more equally valid Lewis structures can be written for the same molecule, yet neither is correct. Example: O3 (ozone) Since both of these structures imply that one bond is shorter than the other, neither is correct. Actual evidence indicates that both bonds are the same length. Connecting both structures by a double-headed arrow implies that the actual structure is a kind of hybrid of the two possibilities.

Polyatomic Ions Multiple atoms with a charge. Usually contain covalent bonds. Example: CN- Show brackets and charges to indicate change in electron number.

Coordinate Covalent Bond When both electrons in bond pair come from one atom. Example:NH4+ Most polyatomic cations and anions contain covalent and coordinate covalent bonds. Can be shown as an arrow in the structural formula pointing away from the atom where the electrons originated.

Two types in molecules: (both are different from ferromagnetism) Magnetisms? Two types in molecules: Diamagnetic – all electrons are paired slightly repelled by a magnet Paramagnetic – one or more unpaired electrons attracted to a magnet Mass will appear greater in a magnetic field (both are different from ferromagnetism)

When the octet rule does not work. Molecules with odd # of electrons Exceptions When the octet rule does not work. Molecules with odd # of electrons NO

Some molecules complex with others to complete an octet BF3NH3

Some have expanded octets When there are more than an octet and it is obvious, turn the dots on the central atom into bonds. Then place the lone pairs on the terminal atoms. PCl5 and SF6 (expanded since after the 3rd energy level “d” is there)

Overview of Exceptions Phosphorus can make 5 bonds Sulfur can make 6 bonds Boron can make 3 bonds Beryllium can make 2 bonds

Shape Theory Ways to explain the shape of molecules. Hybridization (Next week’s discussion) VSEPR Theory (Today and Monday)

VSEPR Theory Stands for: Valence Shell Electron Pair Repulsion Theory Electron pairs repel each other, whether they are in chemical bonds (bonding pairs) or unshared (lone pairs). Electron pairs assume orientations about an atom to minimize repulsions

Applying the VSEPR Theory Draw a possible Lewis structure of the molecule. Determine the number of bonding pairs and lone pairs on the central atom. Find shape on handout and establish the geometry of the molecule about the central atom. If there is more than one central atom shape is described about all of the central atoms.