02 - Lewis Structures - Notes PDF

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2 - Lewis Structures

SCH3UE – Chemical Bonding and Structure

Date: ______________________________________________

Lewis Structures Drawing Bohr Rutherford Diagrams Recall Bohr’s model of the atom

Only a certain number of electrons can fit into each energy level ______ in the first level ______ in the second level ______ in the third level Example: Nitrogen Has 7 electrons Fill the orbitals using Hund’s rule Each electron goes by itself unless there is no more space

Drawing Lewis Dot Diagrams Drawing Bohr Rutherford diagrams can get difficult as we get to the larger atoms We want to find a short cut Lewis Dot Diagrams are only interested in the _______________________________________________ These are the electrons that are involved in ___________________________________________ We use the ______________________________________________ to represent the inner non-bonding electrons and the nucleus Use ________________________ around the elemental symbol to represent the electrons Recall the Bohr Rutherford Diagram for Sodium

Examples Carbon

Calcium

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2 - Lewis Structures

SCH3UE – Chemical Bonding and Structure

Lewis Structures Procedure: Locate the ____________________ atom in the molecule. In simple molecules, the _____________ atom will likely be the one which is the only one of its kind in the molecule Draw the kernel of the ___________________ atom then place the _______________________________ of the atom around the kernel using dots Draw the _____________________________________ of the other atoms involved in the compound The atoms should be arranged around the central atom in such a manner as to complete the ___________________________ of the central atom Add or subtract electrons as necessary for ____________________________________________ Examples: Methane, CH4

Draw OF2

Ammonium ion

Hydroxide ion

Formal Charges A Lewis structure shows how electrons are _________________________________ in a molecule For some chemical compounds, more than ___________________________________________________ can be drawn Example: SCN-

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2 - Lewis Structures

SCH3UE – Chemical Bonding and Structure

Which of the Lewis Structures is correct? We use __________________________________________ to determine the correct structure Formal Charge is the ____________________________ an atom would have if all the atoms in the molecule had the same _____________________________________________ This is a _____________________________________ charge for each atom in the molecule

Calculating formal charge 1) All ____________________________ electrons are assigned to the atom on which they are found 2) For any _______________, ___________________________________ electrons are assigned to each atom in the bond

Criteria used to select most probable Lewis structure: 1) Lewis structure in which the atoms bear formal charges closest to ________________________ 2) Lewis structure in which any ________________________________ charges reside on the more ______________________________________________ atom Examples: SCN-

OCN-

Recall that in past years, the maximum number of electrons in any given orbital was ________________ This still holds true for periods __________________________ We recently learned that the maximum number of electrons in an orbital is given by ________________________ This expanded valence comes into play when we are drawing Lewis structures _____________________________ and _____________________ can reach into the ________ orbital and accommodate up to ____________ electrons in the outer shell SO42-

PO43-

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