Upload
petula
View
37
Download
0
Embed Size (px)
DESCRIPTION
Chapter 16 Notes, part II. More on Covalent Bonding. Drawing Line Diagrams. A line diagram replaces the circled shared pair of electrons with a line. Lines must be straight and short; double bonds should look like an equal sign. Draw line diagrams for: H 2 O CO 2 HCN. Resonance. - PowerPoint PPT Presentation
Citation preview
Chapter 16 Notes, part IIMore on Covalent Bonding
Drawing Line Diagrams
• A line diagram replaces the circled shared pair of electrons with a line.
• Lines must be straight and short; double bonds should look like an equal sign.
• Draw line diagrams for:
H2O
CO2
HCN
Resonance• If you draw the covalent bonding diagram
of some compounds—nitrite for example—there is not only one way to draw it.
• There are two valid ways to show the structure of nitrite. The real structure is an average of the two, and this is called a resonance structure. It is shown by:
Resonance, cont.• Earlier chemists thought the compound
just quickly flipped back and forth between the two structures (or resonated).
• This is proven to be untrue now using bond lengths.
Coordinate Covalent Bonding
• A coordinate covalent bond occurs when one atom gives both electrons to a shared pair between them.
• In a line diagram, instead of a straight line showing a shared pair, the coordinate covalent bond is shown as an arrow.
Sigma and Pi Bonds• How do covalent bonds form between two
elements?
• By the combining of their p orbitals.
Sigma and Pi Bonds• The first bond between two atoms is a
sigma bond () and it forms because of end-to-end overlap of p orbitals.
• Any other bonds between the same atoms would be a pi bond () and they form because of side-to-side overlap of p orbitals.
Sigma and Pi Bonds• Single bond = 1 sigma bond
• Double bond = 1 sigma + 1 pi bond
• Triple bond = 1 sigma + 2 pi bonds
Sigma and Pi Bonds• How many sigma and pi bonds do the
following compounds have?
H2O HCN CS2
NH3 CH2O
SiO2
So, then how…
• If bonding occurs only with p orbitals, how does carbon make 4 bonds?
• By forming hybrid orbitals!
Hybrid Orbitals
• The s-orbital, which is not normally used for bonding, combines with the p-orbitals to make 4 equal energy bonding orbitals.
Hybrid Orbitals
• Some bigger elements will also form hybrid orbitals using their d-sublevel’s orbitals.
• This allows for compounds that wouldn’t normally be able to form—compounds that break the octet rule.
Exceptions to the Octet Rule
• PCl5• SF6
• BF3