1)   Using the observed textures and relative melting points for KI, Salol, citric acid and silicon dioxide, compare the strength of: ionic bond, London force, dipole-dipole forces/hydrogen...

1)   Using the observed textures and relative melting points for KI, Salol, citric acid and silicon dioxide, compare the strength of: ionic bond, London force, dipole-dipole forces/hydrogen bonding forces, and covalent network bonds.

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mathewww | High School Teacher | (Level 1) Honors

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Melting points of solids are determined by the strength of the forces that bind them together. Texture of solid compounds is also a measure of the strength of the forces between the units that form the compound. Stronger the bond, harder is the substance and its appearance and vice versa. Weakly bonded compounds are soft in appearance.

Potassium iodide, KI is an ionic compound, having hard salt like texture, m. p. `681^oC` . The crystals are held together by the electrostatic force of attraction between alternate, closely packed ordered layers of `K^+` and `I^-` ions.

Salol is a molecular solid, having a soft texture, m. p. `41^oC` . The molecules are held together in their crystal lattice by London dispersion forces.

Citric acid is a solid organic compound held together by hydrogen bonds which is a particularly strong interaction of the dipole-dipole type, involving hydrogen. It has a salt like appearance, m. p. `153^oC` .

Silicon dioxide is a covalently bonded network solid, very hard and brittle, m. p. `gt 1600^oC` . The molecules are held together in their crystal lattice by pure covalent bonds.

A glance of the relative melting points and textures of the given solid compounds reflect that the weakest forces are intermolecular London dispersive forces found in molecular solids like salol. Next comes the hydrogen bonding forces found in citric acid molecules. Ionic bonds such as in KI are relatively strong and the strongest forces are the covalent forces that bind atoms in covalent network soilds like SiO2.

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