Ch. 11 FLASHCARDS (Intermolecular forces, Physical Properties, Solids)

The principal source of the difference in the normal boiling points of ICl (97 C; molecular mass 162 amu) and Br2 (59 C; molecular mass 160 amu) is __________.

Br2 has a lower boiling point because the Dispersion Forces among the Br2 molecules are weaker than the dipole/dipole interactions among similarly massed ICl molecules

Which one of the following substances will NOT have hydrogen bonding as one of its intermolecular forces? A) HF B) NH3 C. H2S D. H2O

C. H2S (not polar enough to form H bonds)

The reason that CH4, has much lower boiling point than SnH4 is because

CH4 has smaller electron clouds, so is less polarizable (its induced dipole forces are weaker)

This IMF occurs in polar molecules. Positive end of one molecule is attracted to the negative end of an adjacent molecule.

Dipole/Dipole Interaction

Strong intermolecular forces in a substance are manifested by __________. A) high critical temperatures (the highest temp. that a substance can be found as a liquid) B) high boiling point C) low vapor pressure D) high heats of fusion and vaporization E) all of the above

E - all of these

Which one of the following should have the lowest boiling point? A) HCl B) H2S C) PH3 D) H2O E) SiH4

E. SiH4

For hydrogen bonding to occur between two molecules, the hydrogen atom in each molecule must be bonded to a very electronegative atom such as _____, _____, or _______.

Fluorine, Oxygen or Nitrogen

A substance has a relatively high melting point, dissolves in water, and behaves as an electrolyte in solution. The bonding must be ____________________.

Ionic

A liquid begins to boil when its __________________equalizes or overcomes the surrounding ___________________.

vapor pressure..........atmospheric pressure

Elemental iodine (I2) is a solid at room temperature. What is the major attractive force that exists among different I2 molecules in the solid?

Relatively strong London Dispersion Forces (due to large atoms)

The predominant intermolecular force in (CH3)2NH is __________. A) ion-dipole forces B) hydrogen bonding C) ionic bonding D) dipole-dipole forces E) London dispersion forces

(B) hydrogen bonding

Why does water have a lower boiling point above sea level?

Above sea level, surrounding atmospheric pressure is lower, so water's vapor pressure can equalize with surrounding AP at a lower temperature.

CH3CH2OH boils at 78 °C and CH3OCH3 boils at − 24 °C, although both compounds have the same composition. This difference in boiling points may be attributed to a difference in...

Hydrogen Bonding

The melting point of MgO is higher than that of NaF. Explain this fact.

In terms of Coulomb's Law, the charges are higher in MgO (2+, 2-) AND the radii of Mg and O are smaller. Thus the ionic bond is stronger in the MgO.

Polar ICl has a boiling point of 92 C. Nonpolar octane C8H18 has a boiling point of 125 C. How would you account for this observation?

In this case, the London Dispersion Forces of the octane are actually stronger (due to the large size of the molecule) than the dipole/dipole interactions of the ICl.

ALL atoms and molecules have _____________ because they have electrons. There is random movement of electrons in a cloud which produce a temporary dipole or dispersal of electrons in a neighboring molecule

Induced Dipole Forces (London Dispersion Forces)

The intermolecular force(s) present in CH4, SiH4, GeH4, SnH4 is/are __________.

London Dispersion Force (Induced dipole)

What IMF is (are) present in methanol CH3OH?

London Dispersion Forces, dipole/dipole interactions and Hydrogen Bonding. (Hydrogen Bonding is the strongest however)

What is the relationship between the melting point (or boiling point) of a substance and the strength of the IMF?

The stronger the IMF, the higher the melting point or boiling point

The enthalpy change for converting 10.0 g of water at 25.0 C to steam at 135.0 C is ________ kJ. The specific heats of ice, water, and steam are 2.09 J/g-C, 4.18 J/g-C, and 1.84 J/g-C, respectively. For H2O, ∆Hfus = 6.01 kJ/mol, and ∆Hvap = 40.67 kJ/mol. (Hint, sketch a segmented heating curve to guide your calculations and watch units!!!)

[10.0 g x .00418 kJ/g C x 75 C] + [ 40.67 kJ x .55 mol] + [10.0 g x 0.00184 kJ/g C x 35.0 C] = 26.2 kJ

A substance conducts in its solid state, has a high melting point, and does not dissolve in water. The solid has a. metallic bonds b. molecular c. ionic bonds d. covalent network

a. metallic (delocalized electron sea electrostatic ally attracted to positive fixed nuclei)

Silicon dioxide (SiO2) is very hard, has a very high melting point, is insoluble in water, and is a nonconductor. It is a(n) a. metallic solid b. molecular solid c. ionic solid d. covalent network solid

d. covalent network solid- like graphite, diamond, silicon

In general, the vapor pressure of a liquid increases as the strength of the intermolecular forces ________________. So you would expect butane C4H10 to have a _____________vapor pressure than water, and a _______________boiling point than water.

decrease............higher..........lower

All bonds and intermolecular forces are ________________in nature.

electrostatic

Salt dissolves in water because the Na+ and Cl- ions form ______________________ interactions with the surrounding water molecules

ion/dipole