# Objectives  I can draw simple Lewis structures of molecules.

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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

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