http://vimeo.com/1041071

Agenda - Introduction to Bonding, Covalent Bonding Lesson: PPT, Demo: Conductivity, Dissolving, Crystal Lattice and Melting Handouts: 1.PPTHANDOUT, 2. Chemical Bonding Worksheet (Covalent Bonding) Text: 1. P. 61-69 - Properties of Molecular Compounds, Lewis Diagrams (O/S), Octet and, Multiple Bonds, (Need-Have Method) HW: 1. Finish all the worksheets 2. P. 65 #1

Covalent Bonding - SHARING ELECTRONS Some elements do not lose or gain electrons easily. For these elements a different type of bonding occurs; Covalent bonding.  Electrons are shared in pairs instead of being transferred. The basis of the bond is still electrostatic attraction with electrons being attracted by two nuclei.  Covalent bonds are formed when a non-metal combines with another non-metal. Since both non-metals have to gain electrons, they achieve this by sharing electrons. No ions are formed!

The non-metals share electrons such that they have 8 outer electrons when counting their own plus those "borrowed" from the atoms bonding with them. They mutually share electrons. Molecule Lewis diagram   H2 OH- NH3 CCl4 H2O HCl

Covalent bonding CCl4 - Covalent HCl - Covalent Cl Cl H H Cl Cl C Cl 04/10/99 CCl4 - Covalent HCl - Covalent Cl Cl H H Cl Cl C Cl NH3 - Covalent NaCl - Ionic Cl [ Cl ]– [Na] + N H H H2O - Covalent H H2 - Covalent O OH– - Covalent H H H H O H

PROPERTIES OF MOLECULAR SUBSTANCES Tend to form small groups of atoms called molecules Exist as solids, liquids or gases at room temperature Solids are often soft and waxy Liquids and solids often are volatile and can evaporate readily [ie. Perfume or mothballs]

PROPERTIES OF COVALENT SUBSTANCES   Low melting and boiling points  Low solubility in water and other polar solvents Soluble in non-polar solvents such as chloroform or ether As solids, liquids or solutions are non conductors of electricity

MULTIPLE BONDS It is common for atoms to share more than one pair of electrons.   a single pair of electrons shared between two atoms forms a single covalent bond a double pair of electrons shared between two atoms forms a double covalent bond a triple pair of electrons between two atoms forms a triple covalent bond

Up to three electrons can be shared between atoms to achieve a stable octet in the valence orbital. Remember an atom can only share the number of valence electrons it has. Representing Molecular Structures - Read pg. 64-67 Write Lewis Dot Diagram for O2 , N2 and C2H2

Multiple bonds CO2 - Covalent HCl - Covalent Na2O - Ionic O C H Cl 04/10/99 Multiple bonds CO2 - Covalent HCl - Covalent Na2O - Ionic O C H Cl [ O ]2– 2[Na]+ H Cl C O NH3 - Covalent I2 - Covalent O2 - Covalent I H N O H N O I O3 - Covalent H C H C Al2O3 - Ionic O 3[ O ]2– 2[Al]3+ O

Need & Have Method - the have/need method will help you determine the number of bonds present in a molecule Show the Lewis dot diagram for the following: CO32-(aq) 1. Find out how many valence electrons are present: Have: 4 e- on Carbon + 3 x 6 e- on Oxygen + 2 e- from charge = 4 + 18 + 2 = 24 e- 2. Find out how many valence electrons are needed to have a stable molecule: Need: 8 e- on Carbon + 3 x 8 e- on Oxygen = 8 + 24 = 32 e- 3. Take the difference of the two numbers and divide by 2 to determine the number of bonds: Difference = 32 -24 = 8 e- # of Bonds = 8 e-/2 e- = 4 BONDS

Always place extra electrons around the central atom. Always remove extra electrons from the central atom. The central atom always has an octet.

Agenda - Non-Octet and Coordinate Covalent Bonds Lesson: PPT, Handouts: 1.PPTHANDOUT, 2. Chemical Bonding Worksheet (Covalent Bonding) Text: 1. P. 61-69 - Properties of Molecular Compounds, Lewis Diagrams (O/S), Octet and, Multiple Bonds, (Need-Have Method) HW: 1. Finish all the worksheets 2. P. 67 #2; P. 69 #1-7

COORDINATE COVALENT BONDS Co-ordinate covalent bonds are those which bond when atoms share pairs of electrons One of the atoms provides one pairs of electrons being shared while the other atom contributes NO electrons to the shared pair Example: Show the Lewis dot diagram for SO3.

Have: 6 e- on Sulfur + 3 x 6 e- on Oxygen = 6 + 18 = 24 e- Need: 8 e- on Sulfur + 3 x 8 e- on Oxygen = 8 + 24 = 32 e- Difference = 32 -24 = 8 e- # of Bonds = 8 e-/2 e- = 4 BONDS

RESONANCE STRUCTURES Electrons are “delocalized” The position of the double bond can vary when the central atom is bonded to identical atoms This allows the double bond to ‘wander’ and the net result is that each bond has the bond strength of 1 1/3 Electrons are “delocalized”

Polyatomic Ions Polyatomic Ions always follow the octet rule. Place the central atom with valance e- Place extra e- around the central atom Place satellite atoms with valance e- Do need/ have calculations Put square brackets and net charge

. Show the Lewis dot diagram for SO42-(aq) Have: 6 e- on Sulfur + 4 x 6 e- on Oxygen + 2 e- from charge = 6 + 24 + 2 = 32 e- Need: 8 e- on Sulfur + 4 x 8 e- on Oxygen = 8 + = 40 e- Difference = 40 - 32 = 8 e- # of Bonds = 8 e-/2 e- = 4 BONDS .

NON-OCTET rule for molecular compounds Many molecular compounds form, that do not follow the simple octet rule. The non- octet rule is applied when the central atom (the element with the lowest electronegativity) has MORE or LESS than eight electrons. In each such case, you will find that it is only the central atom (P or B below) that violates the octet rule. The surrounding atoms always follow the octet rule (8e-). There will be no coordinate covalent or multiple bonds. The central atom will have an even number of electrons around it.  

Example: PCl5 Since the P has to combine with 5 chlorine atoms, simply let it form 5 single covalent bonds, one with each chlorine.  

Example: BF3 Since the B has to combine with 3 fluorine atoms, simply let it form 3 single covalent bonds, one with each fluorine.

How to recognize Molecular Compound that does not follow the octet rule? Involves: Boron (B) Noble Gas, eg. XeF4 2 Halogens in a ratio greater than 1:1, eg. FCl7 4 or more atoms of one kind, eg. PBr5

Which compounds have covalent bonding? Molecular compounds – involve two NON-METALS. These compounds always have covalent bonding. Polyatomic ions (PO4-3, NO-, CN-). These ions are held together with covalent bonds. Example: Show the Lewis dot diagram for compound that forms between elements with these electron configurations: [He]2s22p3 and [Ne]3s23p5

Agenda - MORE Practice of Lewis Dot diagrams Lesson: Take up of all the previous work Handouts: 1.PPTHANDOUT, 2. Chemical Bonding Worksheet (Covalent Bonding) Text: 1. P. 61-69 - Properties of Molecular Compounds, Lewis Diagrams (O/S), Octet and, Multiple Bonds, (Need-Have Method) HW: 1. Finish all the worksheets 2. P. 89 # 36