Presentation on theme: "Objectives I can draw simple Lewis structures of molecules."— Presentation transcript:
Objectives I can draw simple Lewis structures of molecules.
Lewis Dot Structures Lewis Dot Structures show how valence electrons are arranged in atoms and molecules Lewis dot structures for single atoms 1e-2e-3e-4e- 5e-6e-7e-8e- NaMgAlC NO FNe
Rules for covalent bonding Each bond is made up of 2 electrons Each atom wants to reach the same configuration as the noble gases Duet rule: Hydrogen wants 2 valence electrons Octet rule: All other atoms want 8 valence electrons Atoms will share electrons with other atoms so that both get a full valence shell
Drawing Lewis Dots for Compounds Steps: 1. Draw Lewis Dot structures for the individual atoms Double check your numbers of valence e- 2. Put central atom in the center 3. Put other atoms around 4. Draw 2 dots between each pair 5. Fill in other dots up to 8 (except for H) 6. Replace all bonded pairs with lines CH 4 Central atom C H H HH
Practice Lewis Dots NH 3 H 2 O HH H N Total electrons:NH 3 H3H3H3H3 = 3 x 1 = 3 N = 5 = 5 8
Lewis Dot Structures: Part 2 In a covalent bond, atoms share electrons.
Lewis Dot Structures: Part 2 A covalent bond in which two atoms share two pairs of electrons is called a double bond.
Lewis Dot Structures: Part 2 A covalent bond in which two atoms share three pairs of electrons is called a triple bond.
Double and Triple Bonds What happens when the total electrons do not match up with the Lewis structure? Example:O 2 Draw the Lewis dot structure: OO Total valence electrons: O2O2O2O2 = 2 x 6 = 12 Single bonded structure uses too many electrons!
Double Bonds If the structure has too many dots, remove lone pairs from two atoms and replace with a double bond In a double bond, the atoms share 4 electrons Replace the bonded pairs with 2 lines OO Lone pairs
Double Bonds Some atoms can have more than one double bond Example: CO 2 Total valence electrons: O2O2O2O2 = 2 x 6 = 12 C = 4 = 4 16COO