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Rohan Kumar posted an Question
June 21, 2020 • 15:19 pm 30 points
  • CSIR NET
  • Chemical Sciences

3. the molecular formula, cash2sno2, of compound a is the same as that of molecule b. it is found that the melting point of b is higher than that of a. explain.

3. The molecular formula, CasH2sNO2, of compound A is the same as that of molecule B. It is found that the melting point of B is higher than that of A. Explain. Discuss the various intermolecular forces of attraction that may influence the difference in their melting points.

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    Shivaji khadake Best Answer

    Hello Student example, hydrogen bonding. Hydrogen bonding occurs when a hydrogen atom combines with either nitrogen, oxygen, or fluorine (H2O). Hydrogen bonding results in the strongest intermolecular forces, and therefore will always have the highest mo and bp. Intermolecular forces are the bonds which adjacent molecules form. There can be many types of intermolecular forces (NOTICE: these are NOT INTRAmolecular forces, i.e. Covalent or ionic!). Some types of intermolecular forces are ion:ion, ion:dipole, hydrogen bonds, dipole:dipole, induced dipole:dipole, and induced dipole:induced dipole. These have been ordered from highest strength to lowest strength. Therefore, the melting/boiling points of these would go from highest to lowest as well. This is because melting/boiling requires the disruption of intermolecular forces (to varying degrees, melting less so than boiling). To disrupt or break an intermolecular force, energy needs to be added (endothermic). Therefore, if a bond has a lot of energy (e.g. ion:ion) it takes a lot of energy to input to break, therefore the temperature of the melting/boiling point is higher than a weaker intermolecular force (e.g. dipole:dipole). Types of force of force of attraction s lonic Forces Hydrogen Bonding Van Der Waals Dipole-Dipole Interactions Van der Waals Dispersion Forces (“London forces”) Hydrogen bonding occurs in molecules containing the highly electronegative elements F, O, or N directly bound to hydrogen. Since H has an electronegativity of 2.2 (compare to 0.9 for Na and 0.8 for K) these bonds are not as polarized as purely ionic bonds and possess some covalent character. However, the bond to hydrogen will still be polarized and possess a dipole. Other groups beside hydrogen can be involved in polar covalent bonding with strongly electronegative atoms. For instance, each of these molecules contains a dipole: These dipoles can interact with each other in an attractive fashion, which will also increase the boiling point. However since the electronegativity difference between carbon (electronegativity = 2.5) and the electronegative atom (such as oxygen or nitrogen) is not as large as it is for hydrogen (electronegativity = 2.2), the polar interaction is not as strong. So on average these forces tend to be weaker than in hydrogen bonding. The weakest intermolecular forces of all are called dispersion forces or London forces. These represent the attraction between instantaneous dipoles in a molecule. Think about an atom like argon. It’s an inert gas, right? But if you cool it to –186 °C, you can actually condense it into liquid argon. The fact that it forms a liquid it means that something is holding it together. That “something” is dispersion forces. Think about the electrons in the valence shell. On average, they’re evenly dispersed. But at any given instant, there might be a mismatch between how many electrons are on one side and how many are on the other, which can lead to an instantaneous difference in charge. thank you for asking this question you can check attached image for intermolecular hydrogen bonding of both the structures.

    cropped8490721141124999703.jpg
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    thanks sir

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    you are welcome

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    Lingareddy 1

    intramolecular hydrogen bonding decreases the melting and boiling point. Intramolecular hydrogen bonding occurs in two atoms of same molecule. It decreases the melting and boiling point because of chelation.

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    Lingareddy 1

    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. Most molecular substances are insoluble (or only very sparingly soluble) in water.

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    explain what is the difference between them. in which compound hygrogen bonding present and why

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    compound A have intra molecular hydrogen bond so decreases the melting point

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