Greetings,
Intermolecular forces are electrostatic attractions between molecules. They are at the heart of a myriad of properties observable on our macroscopic level! There are two types of intermolecular forces - (1) London Dispersion - weak and always present and (2) Dipole-Dipole - much stronger and only present for compounds consisting of molecular dipoles.
When we have an asymmetrical molecule consisting of polar-covalent bonds we also have a molecular dipole (indicated in the diagram below with Greek-Delta symbols representing partial charges). Compounds with these properties tend to be solids and liquids at room temperature. Even very low molecular weight compounds will have properties greatly affected by dipole-dipole interactions. A good example is water.
When we have a symmetrical molecule such as carbon tetrachloride, polar-covalent bonds are present but the molecule itself will not have an overall dipole moment. In this case, London Dispersion Forces will dominate. If the molecule outer atoms are heavy enough (such as chlorine), then the compound will tend to be a liquid at room temperature.
The following diagram shows examples of both types of intermolecular forces.
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The London Dispersion Forces come about by a shifting concentration of electrons (indicated by a cluster of blue 'minus signs') to one side of an atom. When this happens, electrons in an adjacent atom shift away from the increased negative charge density and this shifting continues across and between molecules. Very small electrostatic charges are set up by the resulting formation of partial charges across all of the affected atoms. It should be pointed out, that the cascading electron shifts are very short lived and rare compared to the total number of atoms which could be affected. Even so, because of the immense total number of atoms present, it is statistically probable that London Dispersion Forces will be occurring at very many locations within a sample of carbon tetrachloride; and within a sample of any other element or compound in the liquid state.
The Hydrogen-bonding example of water is the strongest type of dipole-dipole intermolecular attractions and is responsible for the very interesting properties of water, such as high density and high surface-tension. Within the water example, the London Dispersion forces are still 'at play', but are very-much dominated by the Hydrogen Bonding effects.
That's all for this post. My next post will focus on intermolecular forces within solutions!
Have a good one!
"Parent" Site; ExcellenceInLearning.biz
Intermolecular forces are electrostatic attractions between molecules. They are at the heart of a myriad of properties observable on our macroscopic level! There are two types of intermolecular forces - (1) London Dispersion - weak and always present and (2) Dipole-Dipole - much stronger and only present for compounds consisting of molecular dipoles.
When we have an asymmetrical molecule consisting of polar-covalent bonds we also have a molecular dipole (indicated in the diagram below with Greek-Delta symbols representing partial charges). Compounds with these properties tend to be solids and liquids at room temperature. Even very low molecular weight compounds will have properties greatly affected by dipole-dipole interactions. A good example is water.
When we have a symmetrical molecule such as carbon tetrachloride, polar-covalent bonds are present but the molecule itself will not have an overall dipole moment. In this case, London Dispersion Forces will dominate. If the molecule outer atoms are heavy enough (such as chlorine), then the compound will tend to be a liquid at room temperature.
The following diagram shows examples of both types of intermolecular forces.
.png)
The London Dispersion Forces come about by a shifting concentration of electrons (indicated by a cluster of blue 'minus signs') to one side of an atom. When this happens, electrons in an adjacent atom shift away from the increased negative charge density and this shifting continues across and between molecules. Very small electrostatic charges are set up by the resulting formation of partial charges across all of the affected atoms. It should be pointed out, that the cascading electron shifts are very short lived and rare compared to the total number of atoms which could be affected. Even so, because of the immense total number of atoms present, it is statistically probable that London Dispersion Forces will be occurring at very many locations within a sample of carbon tetrachloride; and within a sample of any other element or compound in the liquid state.
The Hydrogen-bonding example of water is the strongest type of dipole-dipole intermolecular attractions and is responsible for the very interesting properties of water, such as high density and high surface-tension. Within the water example, the London Dispersion forces are still 'at play', but are very-much dominated by the Hydrogen Bonding effects.
That's all for this post. My next post will focus on intermolecular forces within solutions!
Have a good one!
"Parent" Site; ExcellenceInLearning.biz
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