Chemical Bonds: the attractive (intramolecular) forces, ie.“ the glue”, strong enough to maintain a group of atoms together for an indefinite amount of time. There are three basic types of bonds: Ionic, Covalent, & Metallic.

IonicCovalentMetallic Bonding  e- transfer   EN > 1.6  Crystal lattice  ions  Na + Cl Na + 3s 1 3s 2 3p 5 Cl -  “salts”  very strong bonds generally between metals and non metals.  Solids at room temp.  Poor conductors of electricity in a solid state +-  sharing  1.6 >  EN > 0  “molecules”  hypothetical charge  H + H H H 1s 1 1s 1 1s 2  orbital overlap  Bonding e- are localized between two atoms  Formed between two nonmetals  “sea” of e-  e- are delocalized. “glue” Bonds

DIPOLE MOMENT & POLARITY Polarity is a term that describes the charge distribution about either a bond or a molecule. POLAR covalent bond If the electrons involved in a bond are unequally distributed along the bond axis and the electrons reside closer to the more electronegative atom, this bond is refered to as a POLAR covalent bond. NONPOLAR covalent bonds If the electrons are equally distributed (shared) along the bond axis then this type of bond is called NONPOLAR covalent bonds. dipole moment A dipole moment can be used to visualize the polarity of the bond and is represented by an arrow pointing towards the more electronegative atom and a “+” on the tail.

POLARITY OF A BOND +  +  +  H-Cl S - N C - O  = 0.9  = 0.5  = 1.0 polar covalent bond. If bonds were formed between any of the above examples, the bond would be refered to as a polar covalent bond. A dipole moment can be drawn in each case because the difference in electronegativity is greateer than zero. The example below has zero difference in electronegativity and no dipole can be drawn. nonpolar covalent bond S - C nonpolar covalent bond  = 0

POLARITY OF MOLECULES Molecules can also be described as either polar or nonpolar. nonpolar molecule polar When the individual dipole moments associated with each bond in the molecule cancel out due to symmetry or if no dipole moment exist, the molecule can be classified as a nonpolar molecule. Nonpolar molecules have no overall dipole moment. Otherwise, if an overall dipole moment exist, the molecule is polar.

Practice Problems 1. Draw the VSEPR sketch for each of the following showing the polarity of each bond. Describe each molecule as either polar or nonpolar. a) PH 3 b) CH 2 Oc) NO 2 - d) CBr 4 e) C 2 H 6 I) O 2 2. Why would NH 3 have a larger dipole moment than NF 3 ? Trigonal pyramidal, polar Trigonal planar, polar bent, polar Tetrahedral, nonpolarTrigonal planar, nonpolar linear, nonpolar Ammonia has a trigonal pyramidal geometry with the dipoles along each N-H bond pointing inwards to the N-atom & the overall dipole is in one direction up through the lone pair of electrons of N. NF 3 has the dipoles pointing outward to each F-atom and out to the lone pair of electrons thus each dipole counteracts the other reducing the overall effect.

Group Study Problems 1. Draw the VSEPR sketch for each of the following showing the polarity of each bond. Describe each molecule as either polar or nonpolar. a) H 2 Sb) GaH 3 c) CF 4 d) CH 2 FCle) C 2 H 2 f) O 3 2. Why would CF 2 H 2 have a larger dipole moment than CCl 2 F 2 ?