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When are intermolecular forces the strongest?

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❶These interactions tend to align the molecules to increase attraction reducing potential energy.

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Types of Intermolecular Forces


Steam will assume both the shape and volume of its container and is extremely compressible. Intermolecular forces IMF are the forces which cause real gases to deviate from ideal gas behavior. They are also responsible for the formation of the condensed phases , solids and liquids.

The IMF govern the motion of molecules as well. In the gaseous phase, molecules are in random and constant motion. Each gas molecule moves independently of the others. In liquids, the molecules slide past each other freely.

In solids, the molecules vibrate about fixed positions. The transitions between the phases, phase changes , can be viewed in terms of a Heating Curve , like the one shown below, for water. It is a plot of time versus temperature. The time axis represents the addition of heat as a function of time.

The longer the time span, the more heat has been added to the system. In this Heating Curve, we are starting with ice at o C. As we add heat, we raise the temperature of the ice. In the solid phase, the allowed motions are in vibrational movements within the molecules. In the case of water, the O-H bonds are stretching and bending. The bond lengths and angles are oscillating around the predicted values.

The amount of heat required to raise the temperature of the ice is determined by the heat capacity of ice, the heat required to change the temperature of 1 gram of ice by 1 o C. The heat capacity of each phase of each substance is unique, and depends on the chemical nature of the substance. When the temperature reaches 0 o C, the melting point of ice, further addition of heat does not change the temperature.

At this phase transition temperature , the added energy goes to changing the Potential Energy of the system.

This is the energy associated with the IMF, which are holding the H 2 O molecules in the solid state. It is coulombic in nature, arising from the attraction of charged species. In the case of H 2 O, it is the attraction between the partial positive charges on the H and the partial negative charges on the O. As we discussed earlier in the semester, these are hydrogen bonds , holding the water molecules in the crystalline structure of ice.

At the phase transition temperature, 0 o C, all of the ice will be converted to liquid water. The increase in temperature is, again, an increase in the KE of the system. The movement of the water molecules will increase in the liquid phase. There is still some degree of hydrogen bonding between molecules, but they are no longer in fixed positions in a crystal lattice.

There is a second phase transition at o C. At this temperature, the water, at o C, is converted to steam at o C. The remaining hydrogen bonds are broken, and all of the water molecules are now moving independently of each other, with no remaining hydrogen bonding. The liquid water is converted to steam.

As soon as this happens, addition of heat raises the temperature of the steam and increases the average kinetic energy of the gas molecules, as predicted by the Molecular Kinetic Theory.

The heat of fusion heat required to melt a solid and heat of vaporization heat required to vaporize a liquid are determined by the strength of the Intermolecular Forces. Substances with high IMF will have higher melting and boiling points. It will require more energy to break the IMF. Most IMF are weaker than chemical bonds.

To break the IMF in ice heat of fusion requires 6. All IMF are electrostatic in nature, the interaction of positive and negative charges. The strength of the IMF will, then, depend on the magnitude of these charges. The strongest IMF is ionic bonding. Water, H 2 O Unless, of course, all the covalent bonds are non-polar, in which case there would be no dipoles to begin with. When two polar molecules are near each other, they will arrange themselves so that the negative and positive sides line up.

There will be an attractive force holding the two molecules together, but it is not nearly as strong a force as the intramolecular bonds.

This is how many types of molecules bond together to form large solids or liquids. Certain chemicals with hydrogen in their chemical formula have a special type of intermolecular bond, called hydrogen bonds. Hydrogen bonds will occur when a hydrogen atom is attached to an oxygen, nitrogen, or fluorine atom. This is because there is a large electronegativity difference between hydrogen and fluorine, oxygen, and nitrogen. As a result of the high electronegativities of fluorine, oxygen, and nitrogen, these elements will pull the electrons almost completely away from the hydrogen.

The hydrogen becomes a bare proton sticking out from the molecule, and it will be strongly attracted to the negative side of any other polar molecules. Hydrogen bonding is an extreme type of dipole-dipole bonding. These forces are weaker than intramolecular bonds, but are much stronger than other intermolecular forces, causing these compounds to have high boiling points.

Silicon dioxide forms a covalent network. Unlike carbon dioxide with double bonds , silicon dioxide forms only single covalent bonds. As a result, the individual molecules covalently bond into a large network. These bonds are very strong being covalent and there is no distinction between individual molecules and the overall network. Covalent networks hold diamonds together. Diamonds are made of nothing but carbon, and so is soot.

Unlike soot, diamonds have covalent networks, making them very hard and crystalline. Van der Waals , or London dispersion forces are caused by temporary dipoles created when electron locations are lopsided.

How do intermolecular forces affect evaporation rate? How do intermolecular forces affect freezing point? How do intermolecular forces affect solubility? How do intermolecular forces affect solvation? How do intermolecular forces affect surface tension and viscosity? When do intermolecular forces of attraction occur?


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Intermolecular forces (dipole-dipole, dispersion and hydrogen bonds). These forces are weaker than chemical (covalent) bonds. Therefore molecular solids are s oft, and have a generally low melting temperature.

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Gases have the strongest intermolecular bonds. a. True b. False Get the answers you need, now!5/5(1).

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Start studying Chemistry True/False. Learn vocabulary, terms, and more with flashcards, games, and other study tools. No. The particles are too far apart for the intermolecular attractions to do much good. Lower the energy enough and the intermolecular bonds will strengthen as the molecules get closer together. You will end up with a liquid and then later a solid when they max out.

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False: Surface tension of liquids increase as Intermolecular Force strength increases. Both O2 and Br2 are non-polar molecules, and have only dispersion forces. Those dispersion forces are stronger for Br2, however, since it has many more electrons (70 vs. 16) than does O2. Yes, intermolecular forces are the strongest in solids. solids > liquids > gases "In solids, the intermolecular forces are very strong, and the constituent particles are closely packed. That is why; solids are incompressible and have high density. In liquids, the intermolecular forces are strong enough to keep the particles tied upon to each other .