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Questions and Answers
In a polar covalent bond, the shift of electrons is towards the atom with:
What type of bond results from unequal sharing of electrons?
Which type of bond involves the sharing of electrons in a way that results in a separation of electric charge?
A coordinate covalent bond forms when:
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What characteristic of a molecule leads to the formation of polar covalent bonds?
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Which chemical property influences the dominance of dispersion forces in a molecule?
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What is the term used to describe the ease with which a dipole can be induced in an atom or molecule?
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Which type of dipole exists in all polar molecules due to the difference in electronegativity values of bonded atoms?
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In a polar substance, how do molecules align in relation to dipoles?
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Which type of dipole is created temporarily due to the influence of a neighboring dipole?
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What dominates the properties of higher molecular weight alcohols in terms of determining solubility?
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Why does ethanol (C4H9OH) have higher O-H bond dipole moment compared to n-pentane (C5H12)?
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What is the term for the intermolecular force of attraction resulting from the displacement of electrons and the formation of an instantaneous dipole?
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Which type of attraction involves the ease with which electron charge density is distorted by an external electric field?
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Which process involves the displacement of electrons in a nonpolar species to form an instantaneous dipole, followed by the induction of a dipole in a neighboring atom or molecule?
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What term describes the attraction between two molecules due to an instantaneous dipole in one molecule inducing a dipole in another molecule?
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Which statement accurately describes dispersion forces?
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What property determines the strength of dispersion forces between molecules?
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Study Notes
Polar Covalent Bond
- A polar covalent bond is a separation of electric charge in a covalent bond, involving a shift of electrons toward the atom with the more negative electron affinity.
- This bond results from unequal sharing of electrons due to differences in electronegativity values of the two atoms.
- Example: H+ → Cl-
Polar Molecules
- Water is a polar molecule, with covalent bonds between hydrogen and oxygen atoms being polar covalent bonds.
- The shared electrons spend more time near the oxygen nucleus, giving it a small negative charge, and near the hydrogen nuclei, giving them small positive charges.
Coordinate Covalent Bond
- A coordinate covalent bond is formed when the lone or non-bonding pairs of electrons in an atom take part in a form of bonding.
- The two electrons being shared by the two atoms are supplied by only one of the participating atoms.
- The atom accepting the electron must have an empty orbital to accommodate the two electrons.
- Example: The bond between ammonia (NH3) and hydrogen ion (H+) to give ammonium (NH4+).
Polarizability
- Polarizability is the ease with which a dipole can be induced in an atom or molecule.
- Polarizability increases with an increased number of electrons in a species.
Dipole-Dipole Interactions
- Permanent dipole: exists in all polar molecules due to differences in electronegativity values of bonded atoms.
- Instantaneous dipole: temporary dipole that exists as a result of fluctuation in the electron cloud.
- Induced dipole: temporary dipole created due to the influence of a neighboring dipole (permanent or instantaneous).
Dipole-Dipole Attractions
- In a polar substance, molecules try to line up with the positive end of one dipole directed toward the negative ends of neighboring dipoles.
- This additional partial ordering of molecules causes a substance to persist as a solid or liquid at temperatures higher than otherwise expected.
- Example: Ethanol and n-pentane, with different molecular masses, but differing O-H bond dipole moments and C-H bond dipole moments.
Van der Waals Forces
- Van der Waals forces result from fluctuations in charge density of particles.
- Examples of van der Waals forces include hydrogen bonding, dispersion forces, and dipole-dipole interactions.
- Properties of Van der Waals forces:
- They are weaker than either ionic or covalent chemical bonds.
- They are not directional.
- They act only over a very short range.
- The interaction is greater when molecules draw closer.
- They are independent of temperature, with the exception of dipole-dipole interactions.
Instantaneous and Induced Dipoles
- The displacement of electrons causes a normally non-polar species to become polar, forming an instantaneous dipole.
- Following this, electrons in a neighboring atom or molecule may be displaced, also producing a dipole, called an induced dipole.
- These two events lead to an intermolecular force of attraction called an instantaneous dipole-induced dipole attraction or dispersion force or London force.
- Dispersion forces exist between all molecules and are much weaker than covalent bonds within molecules.
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Description
Learn about polarizability, dipole-dipole interactions, permanent dipoles, instantaneous dipoles, and induced dipoles in atoms and molecules. Understand how the ease of inducing a dipole is related to polarizability and electron distribution.
