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

Some terms we will be explaining Electronegativity Electron density Polarity Dipole moment Hydrogen bonding Etc…

ELECTRONEGATIVITY IN COVALENT AND IONIC BONDING

Electronegativity Definition A measure of the tendency of an atom to attract electrons towards itself. e-e-

What happens when two atoms of equal electronegativity bond together? Equally electronegative Same tendency to attract the bonding pair of electrons Electrons average half way between the two atoms A 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 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 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 more electronegative than A? Ions have been formed. A has lost control of its electron, and B has complete control over both electrons. Electron pair is dragged right over to B's end of the bond.

Electronegativity Attraction that a bonding pair of electrons feels for a particular nucleus depends on: Number of protons in the nucleus Distance from the nucleus Amount of screening by inner electrons

Pauling’s Scale Electronegativity 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 Scale

Explaining 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 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 DENSITY

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

Electron Density A 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

POLARITY

Dipole Moment Separation of positive and negative charges Formed 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 Molecules A 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 Is this a polar molecule? 1. It has dipoles 2. It does not have rotational symmetry Is this a polar molecule? 1. It has dipoles 2. It does not have rotational symmetry

Polar Molecules? Is this a polar molecule? 1. It has dipoles 2. Dipoles do not cancel one another Is this a polar molecule? 1. It has dipoles 2. Dipoles do not cancel one another Is this a polar molecule? 1. It has dipoles 2. Dipoles do not cancel one another Acetic Acid Acetone

Physical Properties Solvent ◦ 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 + Cl - Na + Cl - Na + Cl -

Na + Cl - Na + Cl - Na + Cl - Na + Cl -

SolventChemical formula Boiling point [7 ] Dielectric constant [8] Density Dipole mome nt Non-polarNon-polar solvents Pentane CH 3 -CH 2 -CH 2 -CH 2 - CH 3 36 °C g/m l 0.00 D CyclopentaneC 5 H °C g/m l 0.00 D Hexane CH 3 -CH 2 -CH 2 -CH 2 - CH 2 -CH 3 69 °C g/m l 0.00 D CyclohexaneC 6 H °C g/m l 0.00 D BenzeneC6H6C6H6 80 °C g/m l 0.00 D TolueneC 6 H 5 -CH °C g/m l 0.36 D 1,4-Dioxane /-CH 2 -CH 2 -O-CH 2 - CH 2 -O-\ 101 °C g/m l 0.45 D ChloroformCHCl 3 61 °C g/m l 1.04 D Diethyl etherCH 3 CH 2 -O-CH 2 -CH 3 35 °C g/m l 1.15 D PolarPolar aprotic solventsaprotic Dichloromethane Dichloromethane (DCM) CH 2 Cl 2 40 °C g/m l 1.60 D Tetrahydrofuran Tetrahydrofuran (THF) /-CH 2 -CH 2 -O-CH 2 - CH 2 -\ 66 °C g/m l 1.75 D Ethyl acetate CH 3 -C(=O)-O-CH 2 - CH 3 77 °C g/m l 1.78 D AcetoneCH 3 -C(=O)-CH 3 56 °C g/m l 2.88 D Dimethylformamide Dimethylformamide (DMF) H-C(=O)N(CH 3 ) °C g/m l 3.82 D AcetonitrileAcetonitrile (MeCN)CH 3 -C≡N82 °C g/m l 3.92 D Dimethyl sulfoxide Dimethyl sulfoxide (DMSO) CH 3 -S(=O)-CH °C g/m l 3.96 D Polar protic solventsprotic Formic acidH-C(=O)OH101 °C g/m l 1.41 D n-Butanol CH 3 -CH 2 -CH 2 -CH 2 - OH 118 °C g/m l 1.63 D IsopropanolIsopropanol (IPA)CH 3 -CH(-OH)-CH 3 82 °C g/m l 1.66 D n-PropanolCH 3 -CH 2 -CH 2 -OH97 °C g/m l 1.68 D EthanolCH 3 -CH 2 -OH79 °C g/m l 1.69 D MethanolCH 3 -OH65 °C g/m l 1.70 D Acetic acidCH 3 -C(=O)OH118 °C g/m l 1.74 D WaterH-O-H100 °C g/m l 1.85 D

SolventChemical formula Boiling point [7 ] Dielectric constant [8] Density Dipole mome nt Non-polarNon-polar solvents Pentane CH 3 -CH 2 -CH 2 -CH 2 - CH 3 36 °C g/m l 0.00 D CyclopentaneC 5 H °C g/m l 0.00 D Hexane CH 3 -CH 2 -CH 2 -CH 2 - CH 2 -CH 3 69 °C g/m l 0.00 D CyclohexaneC 6 H °C g/m l 0.00 D BenzeneC6H6C6H6 80 °C g/m l 0.00 D TolueneC 6 H 5 -CH °C g/m l 0.36 D 1,4-Dioxane /-CH 2 -CH 2 -O-CH 2 - CH 2 -O-\ 101 °C g/m l 0.45 D ChloroformCHCl 3 61 °C g/m l 1.04 D Diethyl etherCH 3 CH 2 -O-CH 2 -CH 3 35 °C g/m l 1.15 D PolarPolar aprotic solventsaprotic Dichloromethane Dichloromethane (DCM) CH 2 Cl 2 40 °C g/m l 1.60 D Tetrahydrofuran Tetrahydrofuran (THF) /-CH 2 -CH 2 -O-CH 2 - CH 2 -\ 66 °C g/m l 1.75 D Ethyl acetate CH 3 -C(=O)-O-CH 2 - CH 3 77 °C g/m l 1.78 D AcetoneCH 3 -C(=O)-CH 3 56 °C g/m l 2.88 D Dimethylformamide Dimethylformamide (DMF) H-C(=O)N(CH 3 ) °C g/m l 3.82 D AcetonitrileAcetonitrile (MeCN)CH 3 -C≡N82 °C g/m l 3.92 D Dimethyl sulfoxide Dimethyl sulfoxide (DMSO) CH 3 -S(=O)-CH °C g/m l 3.96 D Polar protic solventsprotic Formic acidH-C(=O)OH101 °C g/m l 1.41 D n-Butanol CH 3 -CH 2 -CH 2 -CH 2 - OH 118 °C g/m l 1.63 D IsopropanolIsopropanol (IPA)CH 3 -CH(-OH)-CH 3 82 °C g/m l 1.66 D n-PropanolCH 3 -CH 2 -CH 2 -OH97 °C g/m l 1.68 D EthanolCH 3 -CH 2 -OH79 °C g/m l 1.69 D MethanolCH 3 -OH65 °C g/m l 1.70 D Acetic acidCH 3 -C(=O)OH118 °C g/m l 1.74 D WaterH-O-H100 °C g/m l 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)

SolventChemical formula Boiling point [7 ] Dielectric constant [8] Density Dipole mome nt Non-polarNon-polar solvents Pentane CH 3 -CH 2 -CH 2 -CH 2 - CH 3 36 °C g/m l 0.00 D CyclopentaneC 5 H °C g/m l 0.00 D Hexane CH 3 -CH 2 -CH 2 -CH 2 - CH 2 -CH 3 69 °C g/m l 0.00 D CyclohexaneC 6 H °C g/m l 0.00 D BenzeneC6H6C6H6 80 °C g/m l 0.00 D TolueneC 6 H 5 -CH °C g/m l 0.36 D 1,4-Dioxane /-CH 2 -CH 2 -O-CH 2 - CH 2 -O-\ 101 °C g/m l 0.45 D ChloroformCHCl 3 61 °C g/m l 1.04 D Diethyl etherCH 3 CH 2 -O-CH 2 -CH 3 35 °C g/m l 1.15 D PolarPolar aprotic solventsaprotic Dichloromethane Dichloromethane (DCM) CH 2 Cl 2 40 °C g/m l 1.60 D Tetrahydrofuran Tetrahydrofuran (THF) /-CH 2 -CH 2 -O-CH 2 - CH 2 -\ 66 °C g/m l 1.75 D Ethyl acetate CH 3 -C(=O)-O-CH 2 - CH 3 77 °C g/m l 1.78 D AcetoneCH 3 -C(=O)-CH 3 56 °C g/m l 2.88 D Dimethylformamide Dimethylformamide (DMF) H-C(=O)N(CH 3 ) °C g/m l 3.82 D AcetonitrileAcetonitrile (MeCN)CH 3 -C≡N82 °C g/m l 3.92 D Dimethyl sulfoxide Dimethyl sulfoxide (DMSO) CH 3 -S(=O)-CH °C g/m l 3.96 D Polar protic solventsprotic Formic acidH-C(=O)OH101 °C g/m l 1.41 D n-Butanol CH 3 -CH 2 -CH 2 -CH 2 - OH 118 °C g/m l 1.63 D IsopropanolIsopropanol (IPA)CH 3 -CH(-OH)-CH 3 82 °C g/m l 1.66 D n-PropanolCH 3 -CH 2 -CH 2 -OH97 °C g/m l 1.68 D EthanolCH 3 -CH 2 -OH79 °C g/m l 1.69 D MethanolCH 3 -OH65 °C g/m l 1.70 D Acetic acidCH 3 -C(=O)OH118 °C g/m l 1.74 D WaterH-O-H100 °C g/m l 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 Properties

Applications - 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

Dirt

Common Examples Polar ◦ 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

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