DIFFERENT TYPES OF INTEMOLECULAR FORCES INTERMOLECULAR FORCES

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1 DIFFERENT TYPES OF INTEMOLECULAR FORCES Do all the exercises in your studyguide COMPARISON OF THE THREE PHASES OF MATTER. Matter is anything that occupy space and has mass. There are three states of matter: Solid Liquid Gas COMPARISON OF THE THREE PHASES OF MATTER. Matter has three classes THREE STATES OF MATTER. Solid 0 0 C liquid 100 o C gas ICE WATER STEAM H 2O melting freezing evaporating condensation H2 O The intermolar force is the force of attraction between the molecules or between formula units or between formula unit and molecules. For example: The force of attraction between/among the water molecules. The force of attraction between/among the sodium chloride formula units. The force of attraction between/among the sodium chloride and water molecules. The example below shows the different between/among the intermolecular and intramolecular forces on the hydrogen iodide molecule (HI). INTERMOLECULAR FORCE ᵟ- ᵟ- H I H I INTRAMOLECULAR FORCES DIFFERENT TYPES OF THE There are three main types of intermolecular forces. Namely: Dipole-dipole interaction Hydrogen bonding London dispersion force These are collectively called Van der Waals forces. 1

2 DIPOLE DIPOLE INTERACTION This is the force of attraction between the polar molecules; except NOF. Examples are: The force of attraction between HCl molecules DIPOLE-DIPOLE INTERACTION ᵟ- ᵟ- H Cl H Cl DIPOLE DIPOLE INTERACTION The name of the above-mentioned intermolecular force is dipole-dipole interaction. POLAR COVALENT BOND Hydrogen bonding is a bonding between the hydrogen atom of one molecule and a highly electronegative atom of another molecule. Those highly electronegative atoms must be: Nitrogen Oxygen Fluorine (NOF) Hydrogen bonding is a strong dipole-dipole interaction. Example of hydrogen bonding is the bonding between HF molecules. ᵟ- ᵟ- H F H F POLAR COVALENT BONDS Another example of hydrogen bonding is the bonding between molecules. See the figure below. 2

3 INTERACTION ON THE BOILING POINTS OF HYDROCARBONS INTERACTION ON THE BOILING POINTS OF HYDROCARBONS The effect of dipole-dipole interaction on the boiling points of different hydrocarbon is shown below. The boiling point of a substance increase linearly with the molar mass of that substance. C 2 H 6 C 3 H 8 C 4 H 10 This relationship is shown below for the boiling points of different hydrocarbons. CH 4 INTERACTION AND The above-mentioned relationship does not hold for the hydrogen containing compounds that have NOF. The Figure below shows the comparison among the boiling points of the hydrogen containing compounds of group 4A, 5A,6A and 7A. INTERACTION AND The general trends shows that the boiling points increase when the molecular mass increase; except in the molecules containing NOF. This shows that there is a strong intermolecular force between the molecules containing NOF. INTERACTION AND On the figure below; name all the intermolecular forces: Do all the exercises in your studyguide 3

4 INTERMOLECULAR FORCE INVOLVING NON-POLAR MOLECULES These are induced intermolecular forces. The following are examples of the intermolecular forces involving non-polar molecules: Dipole induced dipole interaction. London dispersion forces. DIPOLE -INDUCED DIPOLE INTERACTION This is an interaction between the polar and the non-polar molecules. In the non-polar molecules, the polarity must be induced. The following molecules are examples of some of non-polar molecules: N 2 H 2 Cl 2 DIPOLE INDUCED- DIPOLE The polarity of the above-mentioned molecules can be induced by the distortion of their electron-clouds. For an example: If the electron-cloud of N-N is distorted, it becomes polar at that moment. This can then interact with a polar molecule. For an example: N-N can form dipole induced dipole interaction with H-Cl, as it is shown below: DIPOLE INDUCED-DIPOLE INTERACTION Dipole induced-dipole interaction between HCl and N 2 : DIPOLE INDUCED-DIPOLE INTERACTION ᵟ- H Cl N N This is an interaction between the two non-polar molecules. This is called induced dipole-induced dipole interaction. It is again called LONDON DISPERSION FORCE. In this case, both molecule are non-polar molecules and the polarity is induced. Polar covalent bond Pure covalent bond 4

5 The following molecules are examples of nonpolar molecules: N 2 H 2 CH 4 London dispersion force can be formed between the same or different non-polar molecules. Example of this is the formation of liquid nitrogen; as it is shown below: Example of this is the formation of liquid nitrogen; as it is shown below: N N N N This is the force of attraction between an ionic compound and a polar molecule. Example is the interaction between the water molecule and sodium chloride. In this process, the Na + and the Cl - are solvated by the water molecules. This is called hydration. PURE COVALENT BOND Another example is the interaction between NaCl and HCl: This is shown schematically on the next slide. Ion -dipole interaction between two NaCl and HCl ᵟ- Na + Cl H Cl Ionic bond Polar covalent bond 5

6 BOILING The figure below shows the relationship between the solubility of different gases in water at constant temperature. BOILING The molar masses of different substances are compared with their vap H o and the boiling points of those substances. The figures below show these relationships. 6

7 Do all the exercises in your studyguide 7