Chemical Bonding Chemical compounds A Atoms Combine 1

Chemical Bonding

Chemical compounds A. Atoms Combine 1. To become Stable a. Atoms are stable when they have a full valence energy level • Octet rule: Usually 8 e • Exception: He is stable w/ 2 eb. Atoms gain, lose or share eto achieve a full valence level c. Atoms are held together by a chemical bond

Chemical Bonds, Lewis Symbols, and the Octet Rule • Chemical bond: attractive force holding two or more atoms together. • Ionic bond results from the transfer of electrons from a metal to a nonmetal. • Covalent bond results from sharing electrons between the atoms. Usually found between nonmetals. • Metallic bond attractive force holding pure metals together.

Ionic Compounds A. Ionic Bonds 1. Are formed a. between (+) and (-) ions b. When one atom gains ewhile the other loses e 2. Compounds with ionic bonds are called ionic compounds

Ionic Bonds: One Big Greedy Thief Dog!

Covalent Bonding B. Covalent Bonds 1. Are formed when atoms share e 2. Even sharing results in non-polar covalent bonds 2. Uneven sharing results in polar covalent bonds

Polar Covalent Bonds: Unevenly matched, but willing to share.

Metallic Bonding C. Formed between atoms of metallic elements 1. Electron cloud around atoms 2. Good conductors at all states, lustrous, very high melting points Examples; Na, Fe, Al, Au, Co

Metallic Bonds: Mellow dogs with plenty of bones to go around.

Covalent Bonding B. Covalent Bonds 2. Are formed Between two nonmetals 3. Compounds with covalent bonds are called molecules

Chemical Bonds, Lewis Symbols, and the Octet Rule Lewis Symbols

Learning Check A. X would be the electron dot formula for 1) Na B. 2) K 3) Al X would be the electron dot formula 1) B 2) N 3) P

Drawing Lewis Structures Follow Step by Step Method 1. Total all valence electrons. [Consider Charge] 2. Write symbols for the atoms and guess skeleton structure [ define a central atom ]. 3. Place a pair of electrons in each bond. 4. Complete octets of surrounding atoms. [ H = 2 only ] 5. Place leftover electrons in pairs on the central atom. 6. If there are not enough electrons to give the central atom an octet, look for multiple bonds by transferring electrons until each atom has eight electrons around it.

Exceptions to the Octet Rule • • Central Atoms Having Less than an Octet Relatively rare. Molecules with less than an octet are typical for compounds of Groups 1 A, 2 A, and 3 A. Most typical example is BF 3, with only 6 Formal charges indicate that the Lewis structure with an incomplete octet is more important than the ones with double bonds.

Molecular Shapes: VSEPR • There are five fundamental geometries for molecular shape:

Linear 2 atoms attached to center atom 0 unshared pairs (lone pairs) Bond angle = 180 o Type: AB 2 Ex. : Be. F 2

Trigonal Planar 3 atoms attached to center atom 0 lone pairs Bond angle = 120 o Type: AB 3 Ex. : Al. F 3

Tetrahedral 4 atoms attached to center atom 0 lone pairs Bond angle = 109. 5 o Type: AB 4 Ex. : CH 4

Trigonal Bipyramidal 5 atoms attached to center atom 0 lone pairs Bond angle = • equatorial -> 120 o • axial -> 90 o Type: AB 5 Ex. : PF 5

Octahedral 6 atoms attached to center atom 0 lone pairs Bond angle = 90 o Type: AB 6 Ex. : SF 6

These are for molecules with both paired and unshared (lone) pairs of electrons around the central atom.

Bent 2 atoms attached to center atom 2 lone pairs Bond angle = 104. 5 o Type: AB 2 E 2 Ex. : H 2 O

Trigonal Pyramidal 3 atoms attached to center atom 1 lone pair Bond angle = 107 o Type: AB 3 E Ex. : NH 3

Figure 9. 3 Hyper. Chem

Summary of VSEPR Molecular Shapes e-pairs Notation Name of VSEPR shape Examples 2 AX 2 Linear Hg. Cl 2 , Zn. I 2 , CS 2 , CO 2 3 AX 3 Trigonal planar BF 3 , Ga. I 3 AX 2 E Non-linear (Bent) SO 2 , Sn. Cl 2 AX 4 Tetrahedral CCl 4 , CH 4 , BF 4 - AX 3 E (Trigonal) Pyramidal NH 3 , OH 3 - AX 2 E 2 Non-Linear (Bent) H 2 O , Se. Cl 2 AX 5 Trigonal bipyramidal PCl 5 , PF 5 AX 4 E Distorted tetrahedral (see-sawed) Te. Cl 4 , SF 4 AX 3 E 2 T-Shaped Cl. F 3 , Br. F 3 AX 2 E 3 Linear I 3 - , ICl 2 - AX 6 Octahedral SF 6 , PF 6 - AX 5 E Square Pyramidal IF 5 , Br. F 5 AX 4 E 2 Square Planar ICl 4 - , Br. F 4 - 4 5 6

Learning Check Determine the molecular geometry of each of the following: A. CCl 4 1) tetrahedral 2) pyramidal 3) angular B. SO 3 1) trigonal planar 2) pyramidal 3) angular C. PCl 3 1) trigonal planar 2) pyramidal 3) angular Timberlake Lecture. PLUS 27

Solution Determine the molecular geometry of each of the following: A. CCl 4 1) tetrahedral B. SO 3 1) trigonal planar C. PCl 3 2) pyramidal Timberlake Lecture. PLUS 28

Polarity Molecular Geometries and Bonding

Just as electrons push away from each other, so do molecules HBr is a polar molecule: dipole-dipole forces. There also dispersion forces between HBr molecules. CH 4 is nonpolar: London dispersion forces, caused by “temporary dipoles”. S O O SO 2 is a polar molecule: dipole-dipole forces. There also dispersion forces between SO 2 molecules.

Intermolecular Forces What type(s) of intermolecular forces exist between each of the following molecules? HBr is a polar molecule: dipole-dipole forces. There also dispersion forces between HBr molecules. CH 4 is nonpolar: dispersion forces. S SO 2 O O SO 2 is a polar molecule: dipole-dipole forces. There also dispersion forces between SO 2 molecules.

Intermolecular Forces Hydrogen Bond The hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond an electronegative O, N, or F atom. A H…B or A A & B are N, O, or F H…A

Intermolecular Forces Dispersion Forces Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules ion-induced dipole interaction dipole-induced dipole interaction