Today’s Do Now 1. Write the formula for chlorine trifluoride. 2. Write the name of NO 2 3. Draw the Lewis dot diagram for Hydrogen. 4. Draw the Lewis dot diagram for Oxygen.

By the end of class today, we will be able to… Draw Lewis structures representing the sharing of electrons in covalent bonds

Fancy Chemistry

Lewis Dot Diagrams Another way to show how many electrons are in an atom Only shows valence electrons One on each side, then double up! X The element symbol Dots indicate valence electrons

Covalent Bonding Vocabulary Review Bond : the force holding a group of atoms together Atoms bond to achieve noble gas configuration (8 v.e. and sometimes 2 v.e.) Ionic: electrons are transferred; between metal and nonmetal Covalent: electrons shared; two nonmetals What is the definition of ‘bond’? Why do atoms bond? What is the difference between an ionic and a covalent bond?

Lewis Dot Diagrams Lewis Dot Diagrams can be used to depict the electrons in a molecule What is the Octet rule??

Octet Rule Chemical compounds tend to form so that each atom has an octet of electrons in its highest energy level (In a Lewis Dot Diagram, all atoms must have 8 electrons. 2 electrons in the case of hydrogen)

Step 1 Determine the type and number of atoms in the molecule H2OH2O 2 Hydrogen atoms 1 Oxygen atom Our subscripts tell us how many atoms of each element exist in the molecule. No subscript? ?? Means 1 atom

Step 2 Determine the total number of valence electrons in the atoms to be combined H2OH2O

Step 3 Arrange the atoms to form a skeleton structure for the molecule H2OH2O O H H Each bond represents 2 electrons: These electrons are shared by both atoms

Hints for creating a skeleton structure: 1.The least-electronegative atom is central 2. If Carbon is present, it is the central atom 3. Hydrogen is NEVER central What is the trend in electronegativity on the periodic table??

Electronegativity: the tendency of an atom to attract shared electrons toward itself

Step 4 Add unshared pairs of electrons so each atom has an octet (except H) H2OH2O O H H

Step 5 Check # of valence electrons used equals the number available. Check that all atoms have 8 v.e.

One More Class Example: CH 3 Cl

Individual Guided Practice Write the following answers on your desk Every person will complete every problem! 100%!

Question #1 How many valence electrons are in the molecule Cl 2 O ?

Question #1 How many valence electrons are in the molecule Cl 2 O ? 20

Question #2 Draw the Lewis Dot Diagram for the molecule Cl 2 O

Question #3 Draw the Lewis Dot Diagram for the molecule CH 3 Br

Question #4 Draw the Lewis Dot Diagram for the molecule NH 3

Question #5 Draw the Lewis Dot Diagram for the molecule N 2 O

Same Process with added steps… Let’s Go Through the Steps of Drawing Lewis Dot Diagrams with the molecule CO 2

Step 1 Determine the type and number of atoms in the molecule CO 2 1 Carbon atom 2 Oxygen atoms

Step 2 Determine the total number of valence electrons in the atoms to be combined CO 2

Step 3 Arrange the atoms to form a skeleton structure for the molecule CO 2 C O O Each bond represents 2 electrons: These electrons are shared by both atoms

Hints for creating a skeleton structure: 1.The least-electronegative atom is central 2. If Carbon is present, it is the central atom 3. Hydrogen is NEVER central What is the trend in electronegativity on the periodic table??

Step 4 Add unshared pairs of electrons so each atom has an octet (except H) CO 2

Step 4.5 (This is NEW for Today!!) Start with single bonds between the bonded atoms and add multiple bonds as needed

Step 5 Check # of valence electrons used equals the number available. Check that all atoms have 8 v.e. (except H)

Let’s Try Another… HCN

Resonance Structures Resonance: a molecule shows resonance when more than one Lewis structure can be drawn for the molecule

Question #1 Draw the Lewis Dot diagram for the molecule O 2

Today’s Homework Naming covalent compounds and drawing Lewis Dot Diagrams worksheet