IIIIIIIV Chemical Bonding Chapter 6 Section 1 & 2 Pages

Chemical Bond  Attractive force between atoms or ions that binds them together as a unit.(valence e - of one atom attracted to the nucleus of another atom).  Bonds tend to form to decrease potential energy or increase stability.  Types are ionic or covalent.

Ionic Bond A cation is attracted to an anion Cation = positively charged ion Anion = negatively charged ion Octet Rule is followed!

Ionic Compounds Tend to form a crystal lattice. Highly ordered Repeating pattern

Ionic Compound metal-nonmetal Two or more elements are combined in a chemical bond by gaining or losing electrons that achieves the octet rule.

Covalent Bonding nonmetal-nonmetal A covalent bond is formed by a shared pair of electrons between two atoms.

Electronegativity zUsing Electronegativity values one can determine the % ionic character. zNonpolar-covalent, equal sharing of electrons. Bonds having 0% to 5% ionic character. Electronegativity differences of 0 to 0.3. zPolar-covalent, unequal sharing of electrons. Bonds having 5% to 50% ionic character. Electronegativity differences between 0.3 to 1.7. zIonic bonding, is a complete transfer of electrons. >50% ionic character. Electronegativity differences of 1.7 to 3.3

Molecule; nonmetal-nonmetal A group of atoms united by covalent bonds. ( polar or non-polar covalent). Diatomic Molecule

Molecular Substances Substance made of molecules DNADNA

*The law of Octet Octet Rule: Atoms tend to gain, lose, or share electrons in order to get a full set of valence electrons. (usually 8 electrons)

Bond Length zIncreases as you go down a group, because the atomic radius increases. zShorter for multiple bonds.

Multiple Bond Length zTriple bond is shorter than double bond, which is shorter than single bond. zWhy? The more electrons in a bond, the stronger the attraction to the positively charged nuclei of the bonding atoms.

Bond Energies KJ/mol zBond Energies- The amount of energy required to break a chemical bond and form neutral isolated atoms. zIn general the higher the bond energy required the stronger the attraction, the shorter the chemical bond. (Data table on page 182)

Exceptions to the Octet Rule zExceptions are those that form bonds that either have less than 8e - or more than 8e - Less than eight: z Hydrogen can form one bond that has 2e- z Boron forms three bonds that contains 6e- More than eight: z Sulfur can form 6 bonds containing 12e- z Phosphorus can form 5 bonds containing 10e-

Lewis Dot Diagrams Lewis Structures zThe use of dots or other symbols to represent bonded and unshared electrons.

2 shared electrons make a bond. Lines show the bond between atoms in a compound. Structural (lines= 2e - )

How to Draw Lewis Structures: Step 1 (N) determine the number of electrons Needed for each atom in the compound. Grp’s 14,15,16,17 all need 8. Hydrogen needs 2. Step 2 (A)determine the number of electrons Available, which is determined by the grp #. Step 3 N – A = e - Shared (S) Step 4 A - S = Unshared (U)

Example: Methane CH 4 4(2) + 1(8) = 16e - Step 1 = Electrons Needed N

C Carbon goes in the middle because it is the singular atom. Step 2 = Electrons Available A 1(4) + 4(1) = 8e- H H H H

C Bonds go between atoms Each bond uses up 2 electrons Step 2 = N – A = S 16 – 8 = 8e - Shared H H H H 4 Bonds use up 8 electrons (4 x 2 = 8) Unshared ? 8 – 8 = 0

Step 1 determine N Step 2 determine A Step 3 N – A = S Step 4 A – S = U Step 1: Ammonia NH 3

N Nitrogen goes in the middle because it is the singular atom. Arrange Atoms H H H

N Bonds go between atoms (6e - ) Each bond uses up 2 e - Step 2:Form Bonds H H H

N  N = 14  A = 8  S = 6  A – S = 2  Used up 6e - with bonds 2 unshared to complete the octet  You’re done! complete the octet H H H

Step 1 N Step 2 A Step 3 N – A = S Step 4 A – S = U Example Formaldehyde CH 2 O

C You would have to guess whether C or O goes in the middle? It is Carbon, because it can form the most bonds, and least electronegative! Arrange Atoms H H O

C Bonds go between atoms Each bond uses up 2 electrons Form Bonds H H O

C  Had total of 20e - from step 1  Used up 6e - with bonds  Need 2 more e - on C  Need 6 more e - on O  NOT ENOUGH TO GO AROUND NEED DOUBLE BOND. Step 3:Distribute remaining electrons H H O Need 2 more e - on carbon to complete octet!

C  Remember the Octet Rule !  Carbon & Oxygen both need 8e -.  They get 8 by sharing 4 e - between them. Double Bonds H H O

C  Represent double bond with a double line.  You are done! Double Bonds H H O

 Double bonds occur in these molecular compounds; Oxygen, Carbon Dioxide  Triple Bonds: Nitrogen Multiple Bonds

Resonance Structures  Molecules that can’t be correctly represented by a single Lewis diagram.  Actual structure is an average of all the possibilities.  Show possible structures separated by a double-headed arrow.

Example: SO 3 O O S O O O S O O O S O