ELECTRONEGATIVITY POLAR BONDS MOLECULAR POLARITY Joshua Yeo Ong Han Wee Danny Li.

ELECTRONEGATIVITYELECTRONEGATIVITYPOLAR BONDSPOLAR BONDSMOLECULAR POLARITYMOLECULAR POLARITY

Joshua YeoOng Han WeeDanny Li

Some terms we will be Some terms we will be explainingexplaining

ELECTRONEGATIVITY IN ELECTRONEGATIVITY IN COVALENT AND IONIC COVALENT AND IONIC BONDINGBONDING

ElectronegativityElectronegativity

DefinitionA measure of the tendency of an

atom to attract electrons towards itself.

e-

What happens when two atoms What happens when two atoms of equal electronegativity bond of equal electronegativity bond together?together?

Equally electronegativeSame tendency to attract the bonding pair of

electronsElectrons average half way between the

two atomsA non-polar bond is formed

(To get a bond like this, A and B would usually have to be the same atom.)

A.K.A - a "pure" covalent bond - where the electrons are shared evenly between the two atoms.

What happens if B is slightly What happens if B is slightly more electronegative than A?more electronegative than A?

B end of the bond has more than its fair share of electrons and so becomes slightly negative.

A end, short of electrons, becomes slightly positive.

In the diagram, - (read as "delta") means “slightly negative”, while + means “slightly positive”.

Polar bondsPolar bonds

This is described as a polar bond. A covalent bond in which there is a separation

of charge between one end and the other ◦ One end is slightly positive and the other slightly

negative. Examples: most covalent bonds. The hydrogen-

chlorine bond in HCl or the hydrogen-oxygen bonds in water.

What happens if B is a lot What happens if B is a lot more electronegative than more electronegative than A?A?

ElectronegativityElectronegativity

Pauling’s ScalePauling’s ScaleElectronegativity cannot be directly

measured and must be calculated from other atomic or molecular properties

Most commonly used method of calculation is that originally proposed by Pauling

Commonly referred to as the Pauling scale, on a relative scale running from 0.7 to 4.0

Electronegativity in Pauling units

Pauling’s ScalePauling’s Scale

Explaining the trendsExplaining the trends

1. Number of protons in the nucleus◦ Proton number increases, charge increases

2. Distance from the nucleus◦ Equal distance since bonding electrons are all in

the same valence shell

3. Amount of screening by inner electrons◦ Same valence shell, equal screening effect

Explaining the trendsExplaining the trends

1. Number of protons in the nucleus◦ Proton number increases, charge increases

2. Distance from the nucleus◦ Increase since number of electron shells and

quantum number increase

3. Amount of screening by inner electrons◦ Increase since number of electrons in inner shells

increase

ELECTRON DENSITYELECTRON DENSITY

Electron DensityElectron DensityElectron density is the measure

of the probability of an electron being present at a specific location. (i.e. how likely you are to find an electron at a particular place)

Electron DensityElectron Density

Heisenberg Uncertainty Principle : you can't know with certainty where an electron is and where it's going next

Electron DensityElectron DensityA region of space

is called an orbital is where the electron will be found 95% of the time

Higher electron density (where the dots are thicker) nearer the nucleus

a 2p orbital

POLARITYPOLARITY

Dipole MomentSeparation of positive

and negative chargesFormed when the

electron density of one side of a molecule is higher than the other

Due to a higher electronegativity

A polar bond must be present

Polar MoleculesA molecule would be polar when:

1. It has dipoles

2. It does not have rotational symmetry / dipoles do not cancel one another

Polar Molecules?

Is this a polar molecule?

1. It has dipoles

2. It does not have rotational symmetry


1. It has dipoles



1. It has dipoles


Polar Molecules?


1. It has dipoles

2. Dipoles do not cancel one another


1. It has dipoles



1. It has dipoles


Acetic Acid

Acetone

Physical PropertiesPhysical PropertiesSolvent

◦ Non-polar solutes are soluble in non-polar solvents (eg. Hexane)

◦ Most organic molecules are relatively non-polar

◦ Polar solutes are soluble in polar solvents (eg. Water the universal solvent)

◦ Mineral salts and most sugars are highly polar

Applications◦ To dissolve certain materials for usage◦ Liquid-liquid separation

Purification and separation of solutes

Na+Cl-

Na+

Na+

Cl-Cl-

Cl- Na+Na+

Na+ Cl-Cl-

Cl-

Cl-

Na+

Na+

Na+Cl-

Na+

Na+

Cl-Cl-

Cl- Na+Na+

Na+ Cl-Cl-

Cl-

Cl-

Na+

Na+

Solvent Chemical formulaBoiling point

[7]

Dielectric constant

[8]

Density Dipole moment

Non-polar solvents

PentaneCH3-CH2-CH2-CH2-

CH3

36 °C 1.840.626

g/ml

0.00 D

Cyclopentane C5H10 40 °C 1.970.751

g/ml

0.00 D

HexaneCH3-CH2-CH2-CH2-

CH2-CH3

69 °C 1.880.655

g/ml

0.00 D

Cyclohexane C6H12 81 °C 2.020.779

g/ml

0.00 D

Benzene C6H6 80 °C 2.30.879

g/ml

0.00 D

Toluene C6H5-CH3 111 °C 2.380.867

g/ml

0.36 D

1,4-Dioxane/-CH2-CH2-O-CH2-

CH2-O-\101 °C 2.3

1.033 g/m

l0.45 D

Chloroform CHCl3 61 °C 4.811.498

g/ml

1.04 D

Diethyl ether CH3CH2-O-CH2-CH3 35 °C 4.30.713

g/ml

1.15 D

Polar aprotic solvents

Dichloromethane (DCM)

CH2Cl2 40 °C 9.11.3266

g/ml

1.60 D

Tetrahydrofuran (THF)

/-CH2-CH2-O-CH2-

CH2-\66 °C 7.5

0.886 g/m

l1.75 D

Ethyl acetateCH3-C(=O)-O-CH2-

CH3

77 °C 6.020.894

g/ml

1.78 D

Acetone CH3-C(=O)-CH3 56 °C 210.786

g/ml

2.88 D

Dimethylformamide (DMF)

H-C(=O)N(CH3)2 153 °C 380.944

g/ml

3.82 D

Acetonitrile (MeCN) CH3-C≡N 82 °C 37.50.786

g/ml

3.92 D

Dimethyl sulfoxide (DMSO)

CH3-S(=O)-CH3 189 °C 46.71.092

g/ml

3.96 D

Polar protic solvents

Formic acid H-C(=O)OH 101 °C 581.21

g/ml

1.41 D

n-Butanol CH3-CH2-CH2-CH2-OH 118 °C 180.810

g/ml

1.63 D

Isopropanol (IPA) CH3-CH(-OH)-CH3 82 °C 180.785

g/ml

1.66 D

n-Propanol CH3-CH2-CH2-OH 97 °C 200.803

g/ml

1.68 D

Ethanol CH3-CH2-OH 79 °C 300.789

g/ml

1.69 D

Methanol CH3-OH 65 °C 330.791

g/ml

1.70 D

Acetic acid CH3-C(=O)OH 118 °C 6.21.049

g/ml

1.74 D

Water H-O-H 100 °C 801.000

g/ml

1.85 D


[7]

Dielectric constant

[8]


Non-polar solvents


CH3

36 °C 1.840.626

g/ml

0.00 D


g/ml

0.00 D


CH2-CH3

69 °C 1.880.655

g/ml

0.00 D


g/ml

0.00 D

Benzene C6H6 80 °C 2.30.879

g/ml

0.00 D

Toluene C6H5-CH3 111 °C 2.380.867

g/ml

0.36 D


CH2-O-\101 °C 2.3

1.033 g/m

l0.45 D


g/ml

1.04 D


g/ml

1.15 D



CH2Cl2 40 °C 9.11.3266

g/ml

1.60 D


/-CH2-CH2-O-CH2-

CH2-\66 °C 7.5

0.886 g/m

l1.75 D


CH3

77 °C 6.020.894

g/ml

1.78 D


g/ml

2.88 D


H-C(=O)N(CH3)2 153 °C 380.944

g/ml

3.82 D


g/ml

3.92 D


CH3-S(=O)-CH3 189 °C 46.71.092

g/ml

3.96 D



g/ml

1.41 D


g/ml

1.63 D


g/ml

1.66 D


g/ml

1.68 D


g/ml

1.69 D


g/ml

1.70 D


g/ml

1.74 D

Water H-O-H 100 °C 801.000

g/ml

1.85 D

These bind to positively charged solutes well due to the highly electronegative atom at one side of the solvent molecule (usually O)


[7]

Dielectric constant

[8]


Non-polar solvents


CH3

36 °C 1.840.626

g/ml

0.00 D


g/ml

0.00 D


CH2-CH3

69 °C 1.880.655

g/ml

0.00 D


g/ml

0.00 D

Benzene C6H6 80 °C 2.30.879

g/ml

0.00 D

Toluene C6H5-CH3 111 °C 2.380.867

g/ml

0.36 D


CH2-O-\101 °C 2.3

1.033 g/m

l0.45 D


g/ml

1.04 D


g/ml

1.15 D



CH2Cl2 40 °C 9.11.3266

g/ml

1.60 D


/-CH2-CH2-O-CH2-

CH2-\66 °C 7.5

0.886 g/m

l1.75 D


CH3

77 °C 6.020.894

g/ml

1.78 D


g/ml

2.88 D


H-C(=O)N(CH3)2 153 °C 380.944

g/ml

3.82 D


g/ml

3.92 D


CH3-S(=O)-CH3 189 °C 46.71.092

g/ml

3.96 D



g/ml

1.41 D


g/ml

1.63 D


g/ml

1.66 D


g/ml

1.68 D


g/ml

1.69 D


g/ml

1.70 D


g/ml

1.74 D

Water H-O-H 100 °C 801.000

g/ml

1.85 D

These bind to negatively charged solutes well using hydrogen bonding from the singular outward H atom(s)

Hydrophilic VS Hydrophobic◦ Hydrophilic likes water◦ Hydrophobic dislike water◦ Polar molecules are hydrophilic◦ Non-polar molecules are hydrophobic◦ Certain molecules have non-polar and

polar ends of the molecule, displaying both non-polar and polar characteristics

◦ This would result in a hydrophobic end and a hydrophilic end

Physical PropertiesPhysical Properties

Applications - SoapApplications - Soap

Soap contains a hydrophilic head and a hydrophobic hydrocarbon tail

Hydrophobic tail is attracted to dirt particles or soap surfaces

Hydrophilic head is attracted to water This forms a link between water and the

dirt molecules When water is run through a soaped dirt

layer the soap will “pull” the dirt off the surface

Common ExamplesPolar

◦Water◦Ammonia

Non-polar◦Carbon dioxide◦Methane

Intermolecular Bonding Van der Waal’s Force

1. Hydrogen bonds: formed between molecules which have a strongly electronegative atom and a hydrogen atom, with the hydrogen gaining a partial positive charge.

2. Permanent Dipole (PD) - PD: one atom of a molecule is distinctly more electronegative than the other. This results in one side having a permanent partial positive charge and the other side having a permanent negative charge

3. Induced Dipole (ID) - ID: random movement of the electrons in the molecule. At any point in time, the electron cloud at one part of the molecule may be more dense than another side of the atom

Thank youThank you

ELECTRONEGATIVITY POLAR BONDS MOLECULAR POLARITY Joshua Yeo Ong Han Wee Danny Li.

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