Key Concepts And Summary
The physical properties of condensed matter can be explained in terms of the kinetic molecular theory. In a liquid, intermolecular attractive forces hold the molecules in contact, although they still have sufficient KE to move past each other.
Intermolecular attractive forces, collectively referred to as van der Waals forces, are responsible for the behavior of liquids and solids and are electrostatic in nature. Dipole-dipole attractions result from the electrostatic attraction of the partial negative end of one dipolar molecule for the partial positive end of another. The temporary dipole that results from the motion of the electrons in an atom can induce a dipole in an adjacent atom and give rise to the London dispersion force. London forces increase with increasing molecular size. Hydrogen bonds are a special type of dipole-dipole attraction that results when hydrogen is bonded to one of the three most electronegative elements: F, O, or N.
First Deputy Managing Director
The managing director is assisted by a First Deputy managing director who, by convention, has always been a citizen of the United States. Together, the managing director and his/her First Deputy lead the senior management of the IMF. Like the managing director, the First Deputy traditionally serves a five-year term.
List of First Deputy Managing Directors
Impact On Access To Food
A number of civil society organisations have criticised the IMF’s policies for their impact on access to food, particularly in developing countries. In October 2008, former United States president Bill Clinton delivered a speech to the United Nations on World Food Day, criticising the World Bank and IMF for their policies on food and agriculture:
We need the World Bank, the IMF, all the big foundations, and all the governments to admit that, for 30 years, we all blew it, including me when I was president. We were wrong to believe that food was like some other product in international trade, and we all have to go back to a more responsible and sustainable form of agriculture.
Former U.S. president Bill Clinton, Speech at United Nations World Food Day, October 16, 2008
The FPIF remarked that there is a recurring pattern: “the destabilization of peasant producers by a one-two punch of IMF-World Bank structural adjustment programs that gutted government investment in the countryside followed by the massive influx of subsidized U.S. and European Union agricultural imports after the WTO‘s Agreement on Agriculture pried open markets.”
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Van Der Waals Dispersion Forces
The weakest intermolecular forces of all are called dispersion forces or London forces. These represent the attraction between instantaneous dipoles in a molecule. Think about an atom like argon. Its an inert gas, right? But if you cool it to 186 °C, you can actually condense it into liquid argon. The fact that it forms a liquid it means that something is holding it together. That something is dispersion forces. Think about the electrons in the valence shell. On average, theyre evenly dispersed. But at any given instant, there might be a mismatch between how many electrons are on one side and how many are on the other, which can lead to an instantaneous difference in charge.
Its a little like basketball. On average, every player is covered one-on-one, for an even distribution of players. But at any given moment, you might have a double-team situation where the distribution of players is lumpy . In the valence shell, this lumpiness creates dipoles, and its these dipoles which are responsible for intermolecular attraction.
The polarizability is the term we use to describe how readily atoms can form these instantaneous dipoles. Polarizability increases with atomic size. Thats why the boiling point of argon is so much higher than the boiling point of helium . By the same analogy, the boiling point of iodine, is much higher than the boiling point of fluorine .
Uneven Distribution Of Electrons
The permanent dipole in water is caused by oxygen s tendency to draw electrons to itself . The 10 electrons of a water molecule are found more regularly near the oxygen atoms nucleus, which contains 8 protons. As a result, oxygen has a slight negative charge . Because oxygen is so electronegative, the electrons are found less regularly around the nucleus of the hydrogen atoms, which each only have one proton. As a result, hydrogen has a slight positive charge .
Dipole-dipole attraction between water molecules: The negatively charged oxygen atom of one molecule attracts the positively charged hydrogen of another molecule.
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Can We Predict The Imf Strength Of Acetone Vs Glycerol
I was recently assigned a lab where I was to observe several properties of the chemicals Acetone and Glycerol then use my observations to predict their overall Intermolecular Force strength.
The properties I observed were:
Surface Tension: Here, I found that Acetone had a much higher surface tension than Glycerol.
Viscosity: Here, I found that Glycerol had a much higher viscosity than Acetone.
Boiling Point: Researching online, I found that Glycerol had a much higher boiling point than Acetone.
Glycerol also took much longer than Acetone to evaporate.
However, this seems to be conflicting evidence. I have learned that a higher surface tension is associated with overall stronger IMFs , but the other pieces of evidence seem to suggest that Glycerol has stronger IMFs.
My question is, can anybody tell me if Acetone’s IMFs really are stronger than Glycerol, or is it the other way around? Additionally, if any of my experimental results seem wrong, can somebody please point them out?
What Is The International Monetary Fund
The International Monetary Fund is an international organization that promotes global economic growth and financial stability, encourages international trade, and reduces poverty. Quotas of member countries are a key determinant of the voting power in IMF decisions. Votes comprise one vote per 100,000 special drawing right of quota plus basic votes. SDRS are an international type of monetary reserve currency created by the IMF as a supplement to the existing money reserves of member countries.
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Applications For Hydrogen Bonds
Hydrogen bonds occur in inorganic molecules, such as water, and organic molecules, such as DNA and proteins. The two complementary strands of DNA are held together by hydrogen bonds between complementary nucleotides . Hydrogen bonding in water contributes to its unique properties, including its high boiling point and surface tension.
Water droplets on a leaf: The hydrogen bonds formed between water molecules in water droplets are stronger than the other intermolecular forces between the water molecules and the leaf, contributing to high surface tension and distinct water droplets.
In biology, intramolecular hydrogen bonding is partly responsible for the secondary, tertiary, and quaternary structures of proteins and nucleic acids. The hydrogen bonds help the proteins and nucleic acids form and maintain specific shapes.
Hydrogen Bonding And Dna
Figure 12. Two separate DNA molecules form a double-stranded helix in which the molecules are held together via hydrogen bonding.
Deoxyribonucleic acid is found in every living organism and contains the genetic information that determines the organisms characteristics, provides the blueprint for making the proteins necessary for life, and serves as a template to pass this information on to the organisms offspring. A DNA molecule consists of two parallel chains of repeating nucleotides, which form its well-known double helical structure, as shown in Figure 12.
Each nucleotide contains a sugar bound to a phosphate group on one side, and one of four nitrogenous bases on the other. Two of the bases, cytosine and thymine , are single-ringed structures known as pyrimidines. The other two, adenine and guanine , are double-ringed structures called purines. These bases form complementary base pairs consisting of one purine and one pyrimidine, with adenine pairing with thymine, and cytosine with guanine. Each base pair is held together by hydrogen bonding. A and T share two hydrogen bonds, C and G share three, and both pairings have a similar shape and structure Figure 13.
Figure 13. The geometries of the base molecules result in maximum hydrogen bonding between adenine and thymine and between guanine and cytosine , so-called complementary base pairs.
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The Four Intermolecular Forces And How They Affect Boiling Points
Properties like melting and boiling points are a measure of how strong the attractive forces are between individual atoms or molecules.
It all flows from this general principle: as bonds become more polarized, the charges on the atoms become greater, which leads to greater intermolecular attractions, which leads to higher boiling points.
There are four major classes of interactions between molecules and they are all different manifestations of opposite charges attract.
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The four key intermolecular forces are as follows:
Ionic bonds > Hydrogen bonding> Van der Waals dipole-dipole interactions> Van der Waals dispersion forces.
Lets look at them individually, from strongest to weakest.
Packing Of Molecular Solids
Molecular compounds pack into repeating structures like metals and ionic lattices. Water forms a hexagonal molecular solid shown below. The open circles are oxygen the shaded ones are hydrogen.
- What is the primary intermolecular force is holding this structure together?
Paraffin Waxes are long chain alkanes from petroleum. Paraffin is a crystalline solid used for candle-making and glide wax on skis and snowboards.
- What intermolecular force is holding this structure together?
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Impact On Public Health
A 2009 study concluded that the strict conditions resulted in thousands of deaths in Eastern Europe by tuberculosis as public health care had to be weakened. In the 21 countries to which the IMF had given loans, tuberculosis deaths rose by 16.6%. A 2017 systematic review on studies conducted on the impact that Structural adjustment programs have on child and maternal health found that these programs have a detrimental effect on maternal and child health among other adverse effects.
In 2009, a book by Rick Rowden titled The Deadly Ideas of Neoliberalism: How the IMF has Undermined Public Health and the Fight Against AIDS, claimed that the IMF’s monetarist approach towards prioritising price stability and fiscal restraint was unnecessarily restrictive and has prevented developing countries from scaling up long-term investment in public health infrastructure. The book claimed the consequences have been chronically underfunded public health systems, leading to demoralising working conditions that have fuelled a “brain drain” of medical personnel, all of which has undermined public health and the fight against HIV/AIDS in developing countries.
Bond Dipoles And Dipole Moments
Polar bonds form between atoms of different electronegativity. This is described as a bond dipole and is represented using an arrow to indicate the direction of
Draw in the partial charges on both NF3 and NH3.
Draw the molecule H2O, with its correct geometry, and show the bond dipoles and partial charges.
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Iondipole And Ioninduced Dipole Forces
Iondipole and ioninduced dipole forces are similar to dipoledipole and dipoleinduced dipole interactions but involve ions, instead of only polar and non-polar molecules. Iondipole and ioninduced dipole forces are stronger than dipoledipole interactions because the charge of any ion is much greater than the charge of a dipole moment. Iondipole bonding is stronger than hydrogen bonding.
An iondipole force consists of an ion and a polar molecule interacting. They align so that the positive and negative groups are next to one another, allowing maximum attraction. An important example of this interaction is hydration of ions in water which give rise to hydration enthalpy. The polar water molecules surround themselves around ions in water and the energy released during the process is known as hydration enthalpy. The interaction has its immense importance in justifying the stability of various ions in water.
An ioninduced dipole force consists of an ion and a non-polar molecule interacting. Like a dipoleinduced dipole force, the charge of the ion causes distortion of the electron cloud on the non-polar molecule.
Example Question #1: Intermolecular Forces
Covalent bonding and ionic bonding
Hydrogen bonding and van der Waals forces
van der Waals forces and metallic bonding
Metallic bonding and covalent bonding
Hydrogen bonding and metallic bonding
Hydrogen bonding and van der Waals forces
There is a key difference between atomic bonds and intermolecular forces. Metallic bonds, ionic bonds, and covalent bonds are all atomic bonds. This means that they are generally stable and relatively irreversible. An atomic bond will change the identity of a compound by adding an atom to the structure.
Intermolecular forces, in contrast, are more transient and less stable. These attractions are constantly broken and reformed as molecules move around. Hydrogen bonds, dipole-dipole interactions, and van der Waals forces are some common examples of intermolecular forces. Intermolecular forces will never change the identity of the molecule and cannot be used to add atoms to a compound.
There is a key difference between atomic bonds and intermolecular forces. Ionic bonds and covalent bonds are atomic bonds, meaning they are intramolecular. This means that they are generally stable and relatively irreversible. An atomic bond will change the identity of a compound by adding an atom to the structure.
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Symmetrical Molecules With No Overall Dipole Moment
Molecules often contain polar bonds because of electronegativity differences but have no overall dipole moment if they are symmetrical. For example, in the molecule tetrachloromethane , the chlorine atoms are more electronegative than the carbon atoms, and the electrons are drawn toward the chlorine atoms, creating dipoles. However, these carbon-chlorine dipoles cancel each other out because the molecular is symmetrical, and CCl4 has no overall dipole movement.
Interactive: Polarity and Attractive Strength: Attractions between polar molecules vary. Choose a pair of molecules from the drop-down menu and pull on the star to separate the molecules. Why does polarity have an effect on the strength of attraction between molecules?
Effects Of The Quota System
The IMF’s quota system was created to raise funds for loans. Each IMF member country is assigned a quota, or contribution, that reflects the country’s relative size in the global economy. Each member’s quota also determines its relative voting power. Thus, financial contributions from member governments are linked to voting power in the organization.
This system follows the logic of a shareholder-controlled organization: wealthy countries have more say in the making and revision of rules. Since decision making at the IMF reflects each member’s relative economic position in the world, wealthier countries that provide more money to the IMF have more influence than poorer members that contribute less nonetheless, the IMF focuses on redistribution.
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Imf And Vapor Pressure
When a substance boils, small bubbles rise to the surface and leave the liquid. These bubbles contain vaporized liquid molecules that have acquired enough energy to enter the vapor phase.
- Draw a cartoon of this process in the beaker.
The vapor pressure of a liquid is the pressure created by any molecules that leave the liquid phase and enter the gas phase.
If the external pressure is greater than the vapor pressure, it will push molecules back into the liquid phase.
If the pressure inside the bubbles is the same or greater than the external pressure, boiling will occur.
A high vapor pressure means:
Lots of the molecules are in the vapor phase
Not many of the molecules are in the vapor phase
Molecules with low boiling points typically have:
high vapor pressures
low vapor pressures
Explain what happens to vapor pressure as a liquid is heated.
Assume that a liquid has a very high vapor pressure. Would you expect the intermolecular forces between the molecules between the liquid molecules to be strong or weak? Explain.
Effect On The Behavior Of Gases
Intermolecular forces are repulsive at short distances and attractive at long distances . In a gas, the repulsive force chiefly has the effect of keeping two molecules from occupying the same volume. This gives a real gas a tendency to occupy a larger volume than an ideal gas at the same temperature and pressure. The attractive force draws molecules closer together and gives a real gas a tendency to occupy a smaller volume than an ideal gas. Which interaction is more important depends on temperature and pressure .
In a gas, the distances between molecules are generally large, so intermolecular forces have only a small effect. The attractive force is not overcome by the repulsive force, but by the thermal energy of the molecules. Temperature is the measure of thermal energy, so increasing temperature reduces the influence of the attractive force. In contrast, the influence of the repulsive force is essentially unaffected by temperature.
When a gas is compressed to increase its density, the influence of the attractive force increases. If the gas is made sufficiently dense, the attractions can become large enough to overcome the tendency of thermal motion to cause the molecules to disperse. Then the gas can condense to form a solid or liquid, i.e., a condensed phase. Lower temperature favors the formation of a condensed phase. In a condensed phase, there is very nearly a balance between the attractive and repulsive forces.
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Geckos And Intermolecular Forces
Geckos have an amazing ability to adhere to most surfaces. They can quickly run up smooth walls and across ceilings that have no toe-holds, and they do this without having suction cups or a sticky substance on their toes. And while a gecko can lift its feet easily as it walks along a surface, if you attempt to pick it up, it sticks to the surface. How are geckos able to do this? Although this phenomenon has been investigated for hundreds of years, scientists only recently uncovered the details of the process that allows geckos feet to behave this way.
Geckos toes are covered with hundreds of thousands of tiny hairs known as setae, with each seta, in turn, branching into hundreds of tiny, flat, triangular tips called spatulae. The huge numbers of spatulae on its setae provide a gecko, shown in Figure 7, with a large total surface area for sticking to a surface. In 2000, Kellar Autumn, who leads a multi-institutional gecko research team, found that geckos adhered equally well to both polar silicon dioxide and nonpolar gallium arsenide. This proved that geckos stick to surfaces because of dispersion forcesweak intermolecular attractions arising from temporary, synchronized charge distributions between adjacent molecules. Although dispersion forces are very weak, the total attraction over millions of spatulae is large enough to support many times the geckos weight.