12.1.2 Intermolecular Forces Flashcards Preview

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Flashcards in 12.1.2 Intermolecular Forces Deck (13)
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1
Q

Intermolecular Forces

A
  • The types of intermolecular attractions exhibited by a substance yield many clues to the behavior of the substance.
  • Molecules with dipole moments align according to their polar attraction.
  • London forces originate from the instantaneous, uneven distribution of the electron cloud around an atom.
  • Hydrogen bond donors contain hydrogen bonded to a very electronegative atom, and hydrogen bond acceptors have lone pairs electrons.
2
Q

note

A
  • The types of intermolecular attractions exhibited by a
    substance yield many clues to the behavior of the substance.
  • The strongest types of intermolecular attractions are
    ion-ion attractions (or charge-charge attractions), in which
    oppositely charged particles are attracted to one another.
  • In ion-dipole attractions, a charged particle attracts a
    molecule with a dipole moment.
  • Dipole-dipole attractions involve the alignment of molecular dipole moments such that the opposing poles are in proximity.
  • London forces (or dispersion forces) are weak intermolecular attractions between nonpolar molecules.
  • Molecules with dipole moments align according to their polar attraction.
  • Unless there are strong intermolecular attractions, small
    molecules (such as ammonia) will tend to be gases at room temperature. Because of the overall dipole moment of ammonia (NH3), it condenses to the liquid phase at –30 ̊C (compared to –195.8 ̊C for N 2 ).
  • Acetone (CH 3 COCH 3 ) is a liquid at room temperature. Acetone has a strong dipole moment because of the difference in electronegativity between carbon and oxygen.
  • Methylene chloride (CH 2 Cl 2 ) has a strong dipole moment because of the high electronegativity of chlorine.
  • London forces originate from the instantaneous, uneven distribution of the electron cloud around an atom. This causes one side of the atom to be more negative than the other, setting up temporary partial charges.
  • The larger the atom, the stronger the London forces. For example, bromine (Br 2 ) has stronger London forces than chlorine (Cl 2 ), so bromine is a liquid at room temperature, while chlorine is a gas. Likewise, iodine (I 2 ) has stronger London forces than bromine, so iodine is a solid at room temperature.
3
Q

note 2

A
  • Since hydrogen does not have core electrons, the nucleus of a hydrogen atom is partially exposed when it is bonded to an atom with a high electronegativity. This allows for a special form of dipole-dipole interaction called a hydrogen bond.
  • Hydrogen bond donors contain hydrogen bonded to a very electronegative atom. For example, the hydrogen atoms in water (H 2 O) are bonded to oxygen atoms, which are very electronegative.
  • Hydrogen bond acceptors have lone pairs electrons. For example, the oxygen atoms in water have two lone pair electrons.
4
Q

Here is a list of substances and the type of force holding the substance together in the condensed state. What is the order of the substances from lowest boiling point to highest boiling point?

A

He, Cl2, PH3, NaCl

5
Q

Which of the following polar substances does not exhibit strong hydrogen bonding?

A

Ammonia

6
Q

The following table shows the name, formula, and phase at room temperature of three substances. All three are held together by London dispersion forces. What property accounts for the difference in the phase?

A

The electron clouds around bromine and iodine are larger and easier to distort, so it is easier to induce temporary dipole moments

7
Q

Which of the following physical properties of a substance does not depend on intermolecular forces?

A

Density

8
Q

London (dispersion) forces are due to what?

A

temporary dipole moments

9
Q

Which of the following molecules is most likely to be polar?

A

NH3

10
Q

The hydrogen-oxygen bond in water is highly polarized. Which of these diagrams correctly shows the net charge and unshared electron pairs formed of hybrid orbitals in water molecules?

A

-

11
Q

Which of these substances is held together in the condensed state only by London forces?

A

I2

12
Q

Which of the following list the intermolecular forces in the correct order from the weakest to strongest force?

A

London forces, dipole-dipole, ion-dipole, ion-ion

13
Q

What are the two factors that results to stronger hydrogen bonding?

A

A high electronegativity value of the atom bound to hydrogen and an unshared lone pair of electrons in the other molecule.

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