CHEM 130 Lecture Notes - Lecture 10: Lone Pair, Electronegativity, Covalent Bond

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16 Sep 2016

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Dipoles: polar molecules: polar molecules with 3+ atoms: Shape f molecule determines whether the dipoles cancel or not. H2o; dipoles do not cancel, molecule is + at one end and - at the other. Determining polarity of a molecule: determine if bonds are polar or non polar, if bonds are polar covalent, draw electron-dot formula and determine if the dipoles cancel. Dipole-dipole attractions and hydrogen bonds: in covalent compounds, polar molecules: Form strong dipole attractions called hydrogen bonds between hydrogen atoms bonded to very electronegative atoms f, o, or n and a lone pair on f, o, or n. Hydrogen bonds are the strongest intermolecular attractive forces except ionic bonds. Dispersion forces: weak attractions between non polar molecules, caused by temporary dipoles that develop when molecules bump into each other, weak, but make it possible for non polar molecules to form liquids and solids.

Related Questions

Choose the wrong statement about intermolecular forces.

Choose an answer

A. The attractions due to the induced dipoles and instantaneous dipole results in London dispersion forces.

B. The weakest force of attraction among the intermolecular forces is van der Waal's forces.

C. Dipole dipole attractions are seen in polar molecules.

D. Hydrogen bond is not an intermolecular attractive force in which hydrogen atom bonds to electronegative atoms of same or different molecules.

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* Circle the intermolecular force(s) that is/are present in each of the following species. [Hint: there may be more than one correct answer.]

Ar (hydrogen bonding, dipole-dipole forces, dispersion forces)

CH4 (hydrogen bonding, dipole-dipole forces, dispersion forces)

HBr (hydrogen bonding, dipole-dipole forces, dispersion forces)

HF (hydrogen bonding, dipole-dipole forces, dispersion forces)

CHCl3 (hydrogen bonding, dipole-dipole forces, dispersion forces)

* For the following pairs of atoms/molecules, circle the species that has the higher boiling point.

Ne or Xe

Cl2 or F2

HBr or HF

HCl or HI

H2O or H2S

* Phase changes always associate with change of enthalpy. For the following situations, name the phase

transition and indicate whether the process is exothermic or endothermic.

(a) Dry ice (solid carbon dioxide) turns to gaseous carbon dioxide.

Answer:

(b) Water vapor turns to liquid water.

Answer:

(d) Iodine vapor turns to solid iodine.

Answer:

(e) Liquid helium turns to helium gas.

Answer:

* True or false

1. Intermolecular forces are stronger than ionic and covalent bonds. Answer:

2. For molecules with similar size and molar mass, those with higher polarity would have higher boiling

point. Answer:

3. Ion-dipole forces exist between ionic potassium bromide and polar water.

Answer:

4. Dispersion forces exist between argon and helium. Answer:

5. Instantaneous dipoles exist in all molecules and atoms. Answer:

6. The strength of dispersion forces depends on the molar mass but the shape of the molecules have no effect on dispersion forces. Answer:

7. Ice has a higher density than water because ice has an ordered cagelike structure. Answer:

8. Liquids with weaker intermolecular interactions have lower viscosity. Answer:

9. Viscosity decreases with increasing temperature. Answer:

10. For any molecules, the heat of vaporization is always lower than the heat of fusion because it takes more energy to make molecules to move past one another in a solid lattice. Answer:

CHEM 130 Lecture Notes - Lecture 10: Lone Pair, Electronegativity, Covalent Bond

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