​Lewis Structures (Structural Formulas

• ​Formulas in which

  • atomic symbols=nuclei and inner shell electrons

  • dot pairs & dashes= electron pairs in covalent bonts

    • ​Single bond: a covalent bond where one pair of electrons are shared with each other

  • ​Dots next to one atomic symbol=unshared electrons

​How to Draw Lewis Structures

• ​Start with the electron dot structures for each part of the molecule

• ​Determine the total number of valence electrons available

• ​Arrange the atoms to form a skeleton

  • ​Carbon is always the central atom when present, otherwise the least electronegative atom is

• ​Connect the skeleton with bond pairs

• ​Place the remaining valence electrons around the remaining atoms until they all have 8

  • ​Except for Hydrogen

​Sample Problem On the Board

​Draw the Lewis Structure of iodomethane, CH₃I

• ​Step 1: ​Start with the electron dot structures for each part of the molecule

​Sample Problem On the Board

​Draw the Lewis Structure of iodomethane, CH₃I

• ​Step 1: ​Start with the electron dot structures for each part of the molecule

​Sample Problem On the Board

​Draw the Lewis Structure of iodomethane, CH₃I

• ​Step 1: ​Start with the electron dot structures for each part of the molecule

• ​Step 2: Determine the total number of valence electrons available

​Sample Problem On the Board

​Draw the Lewis Structure of iodomethane, CH₃I

• ​Step 1: ​Start with the electron dot structures for each part of the molecule

• ​Step 2: Determine the total number of valence electrons available

  • ​4+3+7=14

• ​​Arrange the atoms to form a skeleton

​Sample Problem On the Board

​Draw the Lewis Structure of iodomethane, CH₃I

• ​Step 1: ​Start with the electron dot structures for each part of the molecule

• ​Step 2: Determine the total number of valence electrons available

  • ​4+3+7=14

• ​​Arrange the atoms to form a skeleton

  • ​Carbon is Present so it goes in the Middle

​Sample Problem On the Board

​Draw the Lewis Structure of iodomethane, CH₃I

• ​Step 1: ​Start with the electron dot structures for each part of the molecule

• ​Step 2: Determine the total number of valence electrons available

  • ​4+3+7=14

• ​​Arrange the atoms to form a skeleton

• ​​Connect the skeleton with bond pairs

• ​Place the remaining valence electrons around the remaining atoms until they all have 8

​In Class Practice

• ​Do Numbers 1-3 on page 186. You Have 5 Minutes. Turn in at the end of Class.

  • ​If you have time, do Number 4 for Extra Credit

​Multiple Covalent Bonds

• ​Some Elements can share more than one electron pair

  • ​Big three: Carbon, Nitrogen, Oxygen

• ​Double Bond: a covalent bond in which two pairs (4 total) of electrons are shared between two atoms

  • ​All four electrons in a double bond belong to both atoms

• ​Triple Bond: a covalent bond in which three pairs (6 total) of electrons are shared between two atoms

  • ​Carbon and Nitrogen

​Every additional bond added increases the bond energy and makes the bond shorter

​Resonance Structures

• ​Some Molecules can be drawn multiple ways

  • ​Which way is correct? Both of them

• ​Resonance: Bonding in Molecules that can't be represented by a single Lewis Structure