do now: what are the three types of bonds? compare them. which compounds contain which bonds? why?
TRANSCRIPT
Do Now:What are the three types of bonds?Compare them. Which compounds contain which bonds?Why?
Metallic Bond
•Properties of metals? High electrical and thermal conductivity, luster (shiny), malleable, ductile
Valence electrons are delocalized. The bond results from the electrostatic attraction between the delocalized electrons and the metallic ions.
Positive ions (cations) in a "sea"
of delocalized electrons.
Ionic Bond
•Transfer of electrons•Metals lose elelctron(s) to form positive ions (cations)
•Nonmetals gain electron(s) to form negative ions (anions)
Li. :Cl:
:
. Li+ :Cl:
:
..-
Lower IE More negative EA
Ionic Compounds
•Properties???Brittle, crystalline substances with high melting points, most soluble in water, conduct electricity when melted and in solution,
Lattice Energy
Molecular Compounds - Covalent Bonding
• Gas, Liquid,Solid with generally low melting points, brittle, do not conduct electricity• Looking at hydrogen molecule, H2
• High electron density between nuclei. The atoms are held together because the two positive nuclei are attracted to the concentration of negative charge between them. The shared
pair in a covalent bond acts as “glue”
Lewis Structures
• Use Lewis Dot Diagrams• Lone pairs (nonbonding pairs – unshared)
• Bonding Pairs –shared between two nuclei
Draw Lewis structures for N2, O2, and F2•Compare bond length and bond enthalpy, enthalpy change H to break bond
•Estimate H for synthesis of ammonia
Energy Calculations•Estimate Hf
o for potassium chloride provided with:
•Lattice energy of KCl: -690 kJ/mol•First IE for K: 419 kJ/mol•Electron affinity of Cl: -349 kJ/mol•Bond Energy of Cl2: 239 kJ/mol•Enthalpy of sublimation for K: 64 kJ/mol
Ionic and Covalent Bond are on the extremes, what about HCl•Polar covalent bond
•Dipole moment – measure of is the measure of net molecular polarity, tell us about the charge separation in a molecule.
Electronegativity – ability of atom to attract electrons. Explain trend
•H and O•S and S•Li and Cl
-
What type of bond exists between…
Lewis Structures
•Type of structural formula that uses dots or dashes to indicate bonds
Bromine molecule, Br2
Water, H2O
Ethyne, C2H2
Methane, CH4
DO NOW
•Draw the Lewis Structure for NCl3 and HCN
•Indicate the shared and unshared pairs of electrons
•What is another term for shared electrons?
alencehelllectronairepulsion
VSEPR
This theory states that pairs of valence electrons are arranged as far apart from each
other as possible
Draw Lewis Structures for
• H2, C2H2, BH3, NH3, H2O, PCl5, SF6
• In the last two examples, will you satisfy the octet rule? Explain
Example Shape Angle
H2 and C2H2 Linear 180º
BH3 Trigonal Planar 120º
Methane Tetrahedral~109.5º
Ammonia Trigonal Pyramidal ~107º
Water Bent (V-shaped) ~104.5º
Phosphorus Pentachloride
Trigonal Bipyramidal
90º, 120º
Sulfur hexafluoride
Octaheral 90º
?
A molecule’s attractive forces impacts its melting and boiling points as well as many other properties.
•Will a molecule that is highly attracted to another molecule of its kind have a high boiling point or a low boiling point? In which state will the substance typically be found at room tempterature?
Polarity of Molecule•Polar Molecule (Dipoles) – have a positive end and a negative end
•Nonpolar Molecule - has an equal distribution of electrons and therefore no positive or negative ends
First let’s review: Distinguish between polar and nonpolar bonds. What do those terms mean and how do you make this determination?
Polar or Nonpolar Molecules…
•H2
•CO2
•H2O
Shape of molecule and polarity of bonds determines polarity of molecule.
Valence Bond Theory
• Covalent bonds form when a pair of electrons is shared by overlapping atomic orbitals on adjacent atoms.
Consider HF, draw the valence electron configuration for H and F
2p __ __ __H 1s__ F 2s__
X XX
Methane, CH4
•Draw the valence electron configuration for C and H
Carbon’s four sp3 hybrid orbitals
Add four hydrogen s orbitals
Boron Trihydride, BH3
•Draw the valence electron configuration for B
Boron’s three sp2 hybrid orbitals, has 1 empty p orbital
Add three hydrogen s
orbitals
Ethyne, C2H2
•Draw the valence electron configuration for C
Add two hydrogen s
orbitals
Each carbon has two sp orbitals and two p orbitals
• Sigma () bond – results from end to end overlap of atomic orbitals• Pi ()bond – side be side overlap of atomic orbitals
Which bonds are
Try C2H4
Summary of Valence Bond Theory
Hybridization VSEPR theory shape Example
sp Linear (2) C2H2
sp2 Trigonal planar ( 3) BH3
sp3 Tetrahedral, bent(2 shared, 2 unshared), pyramidal (4)
CH4
Trigonal bipyramidal (5) PCl5Octahedral (6) SF6
sp3d
sp3d2