Chemical Bonds:

1. 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.

2. Bonding Bonds “glue” Ionic Covalent Metallic • e- transfer • DEN > 1.6 • Crystal lattice • ions • Na + Cl Na+ 3s1 3s23p5Cl - • “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 > DEN > 0 • “molecules” • hypothetical charge • H + H H H 1s1 1s1 1s2 • orbital overlap • Bonding e- are localized between two atoms • Formed between two nonmetals • “sea” of e- • e- are delocalized. + -

4. DIPOLE MOMENT & POLARITY Polarity is a term that describes the charge distribution about either a bond or a molecule. 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. If the electrons are equally distributed (shared) along the bond axis then this type of bond is called NONPOLAR covalent bonds. 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.

5. POLARITY OF A BOND +++ H-Cl S - N C - O 2.1 - 3.0 2.5 - 3.0 2.5 - 3.5 D = 0.9 D = 0.5 D = 1.0 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. S - C nonpolar covalent bond 2.5 - 2.5 • D = 0

6. POLARITY OF MOLECULES Molecules can also be described as either polar or nonpolar. 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.

7. 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) PH3 b) CH2O c) NO2- d) CBr4 e) C2H6 I) O2 2. Why would NH3 have a larger dipole moment than NF3? Trigonal planar, polar Trigonal pyramidal, polar bent, polar linear, nonpolar Tetrahedral, nonpolar Trigonal planar, 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. NF3 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.

8. 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) H2S b) GaH3 c) CF4 d) CH2FCl e) C2H2 f) O3 2. Why would CF2H2 have a larger dipole moment than CCl2F2?