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