Bellwork Friday Draw Lewis structures for atoms of magnesium and sulfur. Show how these atoms could combine to form a compound using the Lewis structures you drew.

Chapter 8 Covalent Bonding Unit 11 Part 3 Chapter 8 Covalent Bonding

8.1 Covalent Bonds Covalent bond – Occurs when a pair of electrons is shared between two atoms. Often between two nonmetals. Single covalent bond – two atoms share a single pair of electrons Double covalent bond – two atoms share two pairs of electrons Triple covalent bond – two atoms share three pairs of electrons H H O O N N

Covalent Bonds H H Cl Cl O O N N Lewis dot structures can be useful for representing covalent bonds between elements in a covalent compound. H + H  Cl + Cl  O + O  N + N  H H Cl Cl O O N N

Rules for writing electron dot structures: (use pencil!!!) 1. Add up the valence electrons from all the atoms in the compound. Don’t try to keep track of which electrons come from which atoms. If you are working with an ion, you must add or subtract electrons to account for the charge. H2O (2)H + (1) O (2)(1e-) + (1) (6e-) = 8e-

Rules for writing electron dot structures: 2. Put the element that you have the fewest of as the central element. (Make it symmetrical) Put the elements in spatial order. H2O (2) H + (1) O H O H

Rules for writing electron dot structures: 3. Use a pair of electrons to form a bond between each pair of atoms. H O H

Rules for writing electron dot structures: 4. Arrange the remaining electrons to satisfy the duet rule for hydrogen and the octet rule for all remaining atoms. H O H

Rules for writing electron dot structures: 5. Count the number of electrons represented in the drawn molecule. If two too many electrons are represented: draw a double bond between two elements remove a pair of electrons from each element taking place in the bond. H O H 1 2 3 4 5 6 7 8

EXAMPLES: CH4 1. (1) C + (4) H (1)(4e-) + (4)(1e-) = 8e- 2. Spatial order 3. Draw bonds 4. Octet rule satisfied? 5. # of e- match? H H C H H

EXAMPLES: O C O CO2 1. (1) C + (2) O (1)(4e-) + (2)(6e-) = 16e- 2. Spatial order 3. Draw Bonds 4. Octet rule satisfied? 5. # of e- match? O C O

EXAMPLES: H N H H NH3 1. (1) N + (3)H (1)(5e-) + (3)(1e-) = 8e- 2. Spatial order 3. Draw bonds 4. Octet rule satisfied? 5. # of e- match? H N H H

EXAMPLES: CCl4 1. (1) C + (4) Cl (1)(4e-) + (4)(7e-) = 32e- 2. Spatial Order 3. Draw bonds 4. Octet rule satisfied? 5. # of e- match? Cl Cl C Cl Cl

[ ]+ (1)(5e-)+ (4)(1e-) - (1)(1e-) = 8e- EXAMPLES: NH4+ 2. Spatial order 3. Draw bonds 4. Octet rule satisfied? 5. # of e- match? H [ ]+ H N H H

[ ] EXAMPLES: SO42- 1. (1) S + (4) O + (2)(-) (1)(6e-)+ (4)(6e-) + (2)(1e-) = 32e- 2. Spatial Order 3. Draw bonds 4. Octet rule satisfied? 5. # of e- match? [ ] O 2- O S O O

[ ]- (1)(4e-) + (1)(5e-)+ (1)(1e-) = 10e- EXAMPLES: C N CN- 2. Spatial order 3. Draw Bonds 4. Octet rule satisfied? 5. # of e- match? [ ]- C N

[ ] EXAMPLES: CO32- 1. (1) C + (3) O + (2)(-) (1)(4e-)+ (3)(6e-) + (2)(1e-) = 24e- 2. Spatial Order 3. Draw bonds 4. Octet rule satisfied? 5. # of e- match? [ ] 2- O C O O

Exceptions to the Octet Rule: Elements that can have extra electrons! F B F Boron Trifluoride 3 bonds on B(6e-) F F F F S F F F Cl Cl Phosphorous Pentachloride 5 bonds on P (10 e-) Sulfur Hexafluoride 6 bonds on S (12 e-) P Cl Cl Cl

“P B S” bonded to ANY halogen can be an exception! REMEMBER: “P B S” bonded to ANY halogen can be an exception!

[ ] [ ] [ ] Resonance Structures 2- 2- 2- O C O O C O O C O O O O Structures that can occur when it is possible to write two or more valid electron dot structures that satisfy the octet rule. EXAMPLES: CO32- [ ] [ ] [ ] 2- 2- 2- O C O O C O O C O O O O

[ ] [ ] [ ] Resonance Structures - - - O N O O N O O N O O O O NO3- EXAMPLE: NO3- [ ] - [ ] - [ ] - O N O O N O O N O O O O