Why do Atoms Bond?• Stable Arrangement – full outer energy level
What is a Covalent Bond?• Covalent Bond – A chemical bond that results from sharing valence electrons• Molecule – When 2 or more atoms bond covalently – The shared electrons are part of the outer energy level – Generally form between non-metallic elements
Bond Formation• Diatomic Molecules form when TWO atoms form a molecule – Example: N2 , F2 – The sharing of one pair of electrons gives each atom a stable noble gas configuration
Lone Pair Bonding Pair
Single Covalent Bonds• Only one pair of electrons are shared• The shared electrons belong to each atom simultaneously
Lewis Structure• Represent the arrangement of electrons in a molecule• A line or pair of vertical dots between the symbols represent a single covalent bond
Lewis Structures• Group 16 can share 2 electrons and form 2 covalent bonds• Group 15 can form 3 covalent bonds with atoms of nonmetals• Group 14 can form four covalent bonds
Covalent Bonds Continued• Sigma Bond – Single covalent bond – The shared electrons is in an area centered between the two atoms• Double Bonds – Two pairs of electrons are shared between the two atoms – Example: Oxygen• Triple Bonds – 3 paris of electrons are shared between 2 atoms – Example: Nitrogen• Pi Bonds – If bonds have multiple bonds, they have both a sigma and a pi bond. Example: A triple covalent bond has 1 sigma and 2 pi bonds
Strength of Covalent Bonds• Bond Length – The distance between the two bonded nuclei at the position of maximum attraction – As the number of shared electron pairs increases the bond length decreases – The shorter the bond length the stronger the bond • So, the weakest bond is a single covalent bond and the strongest is a triple covalent bond
Bonds and Energy• Energy is released when a bond forms• Energy must be added to break a bond• The amount of energy required to break a covalent bond is called the bond dissociation energy. It is always positive• Endothermic Reaction- a greater amount of energy is required to break the existing bond in the reactants than is released• Exothermic Reaction- more energy is released during broduct bond formation than is required to break bonds in the reactants.
Naming MoleculesWe keep getting smarter….
Basic Rules• Must be a binary molecular compound of 2 NON METALS1. The first element in the formula is named first using the ENTIRE elements name2. The second element in the formula is named using its root and adding the suffix –ide.3. Prefixes are used to indicate the number of atoms of each element that are present in the compound.
Exceptions to the rules • Never use mono when naming the first element• If using a prefix results in two consecutive vowels, drop one to make it easier to sayExample: CO Carbon Monoxide not Monocarbon Monooxide
Lets Practice• CO2• SO2• NF3• CCl4 Your Turn: P 979 Q 2a-f
Common Names• Do you drink Dihydrogen Monoxide?• Do you use Dinitrogen Monoxcide at the dentist?• Some binary molecular compounds have common names• They are water, ammonia, hydrazine, and nitric oxide, and nitrous oxide
Let’s Name Acids• If a compound produces H ions in a compound it is an acid.• 2 types – Binary • H and one other element – Oxyacids • A polyatomic ion containing one or more oxygen atoms
Binary Acids1. The first word has the prefix hydro to name the H part of the compound2. The rest of the 1st word consists of a form of the root of the 2nd element plus the suffix –ic3. The second word is always acid
HCL Hydrogen ChlorineHydrochloric Acid
Exception to rule• Acids containing more than 2 elements with NO OXYGEN• Use the name of the polyatomic ion as the root
Naming Oxyacids1. Root of the oxyacid and the prefix per- or hypo- 1. H are not used as part of the name2. If the name ends with -ate replace it with –ic3. If the name ends with –ite replace it with –ous4. The second word is always acid
You TryP 251 19-24P 979 3
Writing Formulas from Names• The prefixes indicated the number of each atom present• Remember all binary acids contain H and one other element• You will need to know the name of the common oxyanions
Molecular Structures Section 8.3
Structures• Molecular-element symbols and subscripts – Example: PH3• Ball and stick model- atoms are represented by colored spheres• Structural formula- – Most useful – Uses letter symbols and bonds
Lewis Structures Lewis StructuresAnd more Lewis Structures
Resonance Structures• It is possible to have more than one lewis structure• When more than one valid lewis structure can be written for a molecule or ion• Behaves as if it has only one structure• Actual bond length is the average of the bonds in the resonance structures
Exceptions to the Octet• Odd number of valence electrons• Coordinate covalent bond-when one atom donates both of the electrons to be shared with an atom or ion that needs two electrons to form a stable electron arrangement.• Figure 8.16 in your book!• Expanded octets-a central atom with more than 8 valence electrons
Molecular Shapes 8.4
VSEPR Model• The model used to determine the molecular shape• Valence Shell Electron Pair Repulsion• Based on an arrangement that minimizes the repulsion of shared and unshared electron pairs
Bond Angle• The electron pairs in a molecule repel each other like balloons tied together• This causes the atoms to be positioned at a fixed angle to one another• The angle formed by two terminal atoms and the central atom is a bond angle
Hybridization• Occurs when 2 things are combined and the result has characteristics of both• Hybridization is a process in which atomic orbitals mix and form new identical hybrid orbitals.
Hybridization• Hybrid- When two things are combined and the result has characteristics of both• Hybridization- a process in which atomic orbitals mix and form new, identical orbitals