WEEK 8
16MAR2015
MONDAY
Review quiz
Review ionic bonding
8.1 COVALENT BONDING
Monatomic elements? Non-bonded
Diatomic elements: unlike ionic bonds these elements have the same electronegativity so…
Prefix
co-
together; mutually; jointly
partner or subordinate in an activity
to the same degree
(mathematics) of the opposite, of the counterpart
Valence (defined by the IUPAC):
The maximum number of univalent atoms (originally hydrogen or chlorine atoms) that may
combine with an atom of the element under consideration, or with a fragment, or for which an atom
of this element can be substituted.
SHARING VALENT ELECTRONS.
Molecule: an electrically neutral group of two or more atoms held together by chemical
bonds.
Atoms and complexes connected by non-covalent bonds such as hydrogen bonds or ionic
bonds are generally not considered single molecules.
All other elements are in molecules bonded covalently with themselves. We don’t go to the
chemical store and buy elements and mix them to form compounds. We react preexisting
molecules to form different molecules.
MOLECULAR COMPOUND
Molecular compound: a compound that is made from molecules.
Properties:
Most covalent compounds have relatively low melting points and boiling points. While the ions in an ionic compound are strongly attracted to each other, covalent bonds create molecules that can separate from each other when a lower amount of energy is added to them. Therefore, molecular compounds usually have low melting and boiling points.
Covalent compounds usually have lower enthalpies of fusion and vaporization than ionic compounds. The enthalpy of fusion is the amount of energy needed, at constant pressure, to melt one mole of a solid substance. The enthalpy of vaporization is the amount of energy, at constant pressure, required to vaporize one mole of a liquid. On average, it takes only 1% to 10% as much heat to change the phase of a molecular compound as it does for an ionic compound.
Covalent compounds tend to be soft and relatively flexible. This is largely because covalent bonds are relatively flexible and easy to break. The covalent bonds in molecular compounds cause these compounds to take form as gases, liquids and soft solids. As with many properties, there are exceptions, primarily when molecular compounds assume crystalline forms.
Covalent compounds tend to be more flammable than ionic compounds. Many flammable substances contain hydrogen and carbon atoms which can undergo combustion, a reaction that releases energy when the compound reacts with oxygen to produce carbon dioxide and water. Carbon and hydrogen have comparable electronegativies so they are found together in many molecular compounds.
When dissolved in water, covalent compounds don't conduct electricity. Ions are needed to conduct electricity in an aqueous solution. Molecular compounds dissolve into molecules rather than dissociate into ions, so they typically do not conduct electricity very well when dissolved in water.
Many covalent compounds don't dissolve well in water.
There are many exceptions to this rule, just as there are many salts (ionic compounds) that
don't dissolve well in water. However, many covalent compounds are polar molecules that
do dissolve well in a polar solvent, such as water. Examples of molecular compounds that
dissolve well in water are sugar and ethanol. Examples of molecular compounds that don't
dissolve well in water are oil and polymerized plastic.
Note:
Network solids are compounds containing covalent bonds that violate some of these "rules".
Diamond, for example, consists of carbon atoms held together by covalent bonds in a crystalline
structure. Network solids typically are transparent, hard, good insulators and have high melting
points.
MOLECULAR FORMULA
Ionic formulas
NaCl = Na2Cl2
Covalent (molecular) formulas
OH- ≠ H2O2
The molecular formula shows how many of each element is in the
molecule, but not how they are bonded.
Ex: Structural isomers
CH4
Molecular formula Structural formula Perspective drawing
(Skeletal models and Fisher projections)
Ball and stick model Space filling model
Also:
Ribbon diagrams
schematic diagram (Surface representations)
electron density maps
FIGURE 1.16MOLECULAR REPRESENTATIONS
Comparison of (A) space-filling, (B) ball-and-stick, and (C) skeletal models of ATP.
Figure: Crystal structure of the 2:2 TLR5-flagellin complex. Two basic units of 1:1
heterodimers (TLR5-flagellin and TLR5'-flagellin') assemble into a 2:2 complex, organizing
two TLR5 chains in a tail-to-tail orientation.
Irreducible complexity?
TUESDAY
Go over last night’s homework.
Today’s homework Read/reread chapter 8.1, 8.2, 8.3; do p247 #54
N2O4
Coordinate covalent bond
Single bonds H2
Double bonds O2
Triple bonds N2
DRAW ON THE WHITE BOARDS
H2O2 Hydrogen peroxide
CO Carbon monoxide
SO2 Sulfur dioxide
SO3 Sulfur trioxide
CF4 Carbon tetrafluoride
O3 Ozone
N2O Nitrous oxide
HCN Hydrogen cyanide
HF Hydrogen fluoride
HCl Hydrogen chloride
H2O Water
H3O+ hydronium
NH4+ ammonium
SO32- sulfite
HSO3- hydrogen sulfite
PO43- phosphate
H2PO4- dihydrogen phosphate
Rule breakers
(if the molecule’s total valance is an odd number)
NO Nitric oxide
NO2 Nitrogen dioxide
PCl5 Phosphorus pentachloride
SF6 Sulfur hexafluoride
RESONANCE
Resonance is a way of describing delocalized electrons within certain molecules or polyatomic ions.
WEDNESDAY
Bonding theories
Yesterday’s Lewis dots
Lab
Today’s homework Read/reread chapter 8.1, 8.2, 8.3; do p247 #54
BONDS
Sigma bonds:
two s orbital overlaps
End to end p orbitals
s and p orbital overlap
Pi bonding
Edge to edge p p orbital overlap
Weaker than sigma bonds
Bond overlap is above and below bond axis
Hybrid orbitals
The mixing of orbitals
Involves the promotion of one s electron to a p orbital
COULOMB'S LAW
The magnitude of the electrostatic force of interaction between two point charges is directly proportional to the scalar
multiplication of the magnitudes of charges and inversely proportional to the square of the distance between them.[12]
The force is along the straight line joining them. If the two charges have the same sign, the electrostatic force between
them is repulsive; if they have different sign, the force between them is attractive.
https://www.youtube.com/watch?v=q9m-hHg0gFk
https://www.youtube.com/watch?v=Vt8NOdINJ1s
https://phet.colorado.edu/en/simulation/molecule-shapes
THURSDAY
Recap yesterday
Homework p.244 32-37
Take home quiz on Friday due Monday. Lewis dot, orbitals, and other lecture slide material.
BONDS 2.0
Lewis dot and VSEPR as a way to determine structure of a molecule.
Bonds… so far
sigma - σ
pi - π
Orbitals overlap to make bonds.
If an orbital has one electron it is free to bond with another orbital that has one electron.
Orbitals and the shape of electron density… so far
s - spherical
p - dumbbell shaped
d - double dumbbell shaped and one crazy one
f - all crazy shapes
sp3 hybridization - one s orbital mixed with three p orbitals
sp2 hybridization - one s orbital mixed with two p orbitals with one regular p left over (for pi
bonding) This is how a double bond is made.
sp hybridization - one s orbital mixed with one p orbitals with two regular p left over (for pi
bonding) This is how a triple bond is made
SP3 ORBITALS
sp3 orbitals overlap with s orbitals and other sp type orbitals to make sigma bonds
makes single bonds
SP2 ORBITALS
sp2 has an extra p orbital left over to be used for pi bonding.
Can make a double bond
SP ORBITALS
sp has 2 p orbitals left for pi bonding
can make a triple bond
8.4 POLARITY
Attractions outside the molecule.
Intramolecular forces (covalent bonds)
Intermolecular forces
Equal sharing of electrons
Diatomic molecules exhibit non-polar characteristics.
They form non-polar covalent bonds.
The electrons are shared equally
non-equal sharing of electrons
Partial positive and partial negative charge
FRIDAY
Take home quiz due Monday. Try it without notes first!
Review sp hybridization
FUN IN THE LAB (WHAT DID THEY MAKE?)
MATERIALS
1. 532.5cm3 -55/45 mixture of gliadin and glutenin; with fill binders
2. 4.91cm3 -NaHCO
3. 4.91cm3 -refined halite (sieve size #40)
4. 236.6cm3 -partially hydrogenated tallow triglyceride
5. 177.5cm3 -crystalline C12H22O11
6. 177.5cm3 -unrefined C12H22O11
7. 4.91cm3 -methyl ether of protocatechuic aldehyde
8. Two - CaCO3 encapsulated avian albumen-coated protein 9. 473.2cm3 -60/40 theobroma cacao solidified extract/ HFCS 42
10. 236.6cm3 -de-encapsulated legume meats (sieve size #10)
METHOD
To a 2-L jacketed round reactor vessel (reactor #1) with an overall heat-transfer coefficient of
about 100 Btu/F-ft2-hr add one, two, and three with constant agitation.
In a second 2-L reactor vessel with a radial flow impeller operating at 100 rpm add four, five,
six, and seven until the mixture is homogeneous.
To reactor #2 add eight (remove calcium carbonate) followed by three equal portions of the
homogeneous mixture in reactor #1. Additionally, add nine and ten slowly with constant
agitation. Care must be taken at this point in the reaction to control any temperature rise that may
be the result of an exothermic reaction.
Using a screw extrude attached to a #4 nodulizer place the mixture piece-meal on a 316SS sheet
(300 x 600 mm). Heat in a 460K oven for a period of time that is in agreement with Frank &
Johnston's first order rate expression (see JACOS, 21, 55), or until transmittance values equal
430, 550, 600 and 670 nm.
Once the reaction is complete, place the sheet on a 25°C heat-transfer table allowing the product
to come to equilibrium with the surrounding air.
PROPERTIES OF IONIC BONDS AND COVALENT BONDS
Covalent Bonds Ionic Bonds
Polarity Low High
Formation
A covalent bond is formed between two non-
metals that have similar electronegativities.
Neither atom is "strong" enough to attract
electrons from the other. For stabilization,
they share their electrons from outer
molecular orbit with others.
An ionic bond is formed between a
metal and a non-metal. Non-metals(-ve
ion) are "stronger" than the metal(+ve
ion) and can get electrons very easily
from the metal. These two opposite ions
attract each other and form the ionic
bond.
Shape Definite shape No definite shape
What is it?
Covalent bonding is a form of chemical
bonding between two non metallic atoms
which is characterized by the sharing of pairs
of electrons between atoms and other
covalent bonds.
Ionic bond, also known as electrovalent
bond is a type of bond formed from the
electrostatic attraction between two
oppositely charged ions in a chemical
compound. These kinds of bonds occur
mainly between a metallic and a non
metallic atom.
Melting
point low High
Examples Methane (CH4), Hydro Chloric acid (HCl),
NaCl, LiF, MgO
Sodium chloride (NaCl), Sulphuric
Acid (H2SO4 )
Occurs
between Two non-metals One metal and one non-metal
Boiling point Low High
State at room
temperature Solid, Liquid or gaseous Solid
ELECRTONEGATIVITY AND POLARITY
Bonding is dictated by electronegativity
CsF vs NO 3.98-0.79 vs 3.44-3.04
0 is non-polar
from 0 to 1.7 is covalent
Above 1.7 is ionic
Polarity is dictated by bond angle and electronegativity
if the molecule is symmetrical with a central atom surrounded equally by atoms of similar
electronegativity then the molecule will be non-polar.
if there is a difference in electronegativity around the molecule then it is polar.
POLAR MOLECULES
Attractions outside the molecule.
Intramolecular forces (covalent bonds) sigma & pi, polar, nonpolar.
Intermolecular forces (outside of the molecule)
Is it easier to break an intermolecular or an intramolecular force?
Types of intermolecular forces (outside)
1. Van der Waals Forces
a. Dipole interactions (like ionic bonds only much weaker)
b. Dispersion forces (motion of electrons)
2. Hydrogen bonds
a. Special type of dipole interaction
b. 5% power of a covalent bond
PROPERTIES DUE TO INTERMOLECULAR FORCES
Melting and boiling points
Molecular substances tend to be gases, liquids or low melting point solids, because the
intermolecular forces of attraction are comparatively weak.
You don't have to break any covalent bonds in order to melt or boil a molecular substance.
As ionic nature increases melting temperature increases
The size of the melting or boiling point will depend on the strength of the intermolecular
forces.
The presence of hydrogen bonding will lift the melting and boiling points.
The larger the molecule the more van der Waals attractions are possible - and those will also
need more energy to break.
Network solids made from covalent bonds act like ionic compounds (unusually high melting
point)
Some have intermolecular forces that are so strong they break at the same temperatures as
the molecular bonds and therefore just vaporize. Diamond.
In the nonpolar diatomic molecules, the intermolecular attractions between one molecule and its neighbor are van der
Waals dispersion forces. (weakest) They should all be a gas. But….
http://www.chem1.com/acad/webtext/solut/solut-7.html
http://www1.lsbu.ac.uk/water/icosahedral_water_clusters.html