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77 Cards in this Set
- Front
- Back
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The forces that exist BETWEEN molecules are called...
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Intermolecular forces
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What state of matter:
Assumes both volume and shape of its container Is compressible Flows readily Has fast diffusion |
Gas
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What state of matter:
Assumes the shape of the portion of the container it occupies Does not expand to fill the container Is virtually incompressible Flows readily Has slow diffusion |
Liquid
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What state of matter:
Retains its own shape and volume Is virtually incompressible Does not flow Has extremely slow diffusion |
Solid
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T/F: The kinetic energy BETWEEN gas molecules is low, while their overall movement and kinetic energy (temperature) is high, allowing them to fill any container they're in.
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True
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Solids and liquids are not very compressible because...
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They have stronger intermolecular forces that hold the molecules together, so there is less space between each molecule for compression to occur (solids and liquids are sometimes called "condensed phases")
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Solids that possess highly ordered three dimensional structures are said to be...
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Crystalline
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T/F: The state of a substance depends largely on the balance between the kinetic energies of the particles and the interparticle energies of attraction.
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True
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What does compressing a gas do to the intermolecular forces?
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It makes them stronger
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Why do the molecules of something like HCl remain entact when changing phases?
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Because intermolecular forces are what determine a molecule's state at room temperature, and intermolecular forces are much weaker than covalent bonds, so it takes much less energy to break them. So, when melting or boiling, the covalent bond remains intact.
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T/F: In boiling a liquid, the strong the attractive forces are, the higher the temperature at which the liquid boils is.
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True
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Discuss ion-dipole forces and give an example.
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They are the attractions between ions (cations (+) or anions (-)) and polar molecules, which have a positive and a negative end due to different electronegativities. A good example is NaCl (ionic substance) in water (a polar liquid).
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The attraction of one positive end of a polar MOLECULE (covalent bonds) to the negative end of a polar molecule is an example of...
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Dipole-dipole forces
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What creates a net "attraction" in dipole-dipole forces?
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The two like-charged ends of a polar molecule spend less time together than the two oppositely-charged and attractive ends do, so the overall result is attraction between the oppositely charged poles of molecules.
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T/F: In various liquids, for molecules of approximately equal size and mass, the strengths of intermolecular attractions increase with increasing polarity.
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True
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T/F: As the dipole moment of a liquid increases, the boiling point increases.
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True
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When the motion of electrons in a non polar molecule create and instantaneous/momentary dipole moment, this is an example of...
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London Dispersion Forces
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T/F: Dispersion forces really only occur when molecules are closer together, like dipole-dipole forces
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True
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The ease with which the electron distribution in a molecule is distorted (so that dispersion forces can work and interact) is called...
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Polarizability
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T/F: More polarizable molecules have larger dispersion forces.
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True
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Dispersion forces tend to increase in strength with molecular weight. Why?
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Because the larger the molecule, the more electrons there are, and the less pull the nucleus has on them, so they are more likely to disperse and experience an instantaneous dipole moment.
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How do the shapes of molecules affect the strength of intermolecular forces?
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Even in molecules with the same molecular formula, the molecule that is more linear (versus circular) allows for more interaction among the atoms, so the boiling point is much higher and the intermolecular forces between them are much stronger.
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T/F: Even in polar molecules, London dispersion forces are responsible for most of the intermolecular forces, not dipole-dipole forces.
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True
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When two molecules are of the same relative weight, what forces determine which molecule has the greater intermolecular force?
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Dipole-dipole forces, because molecules with the same molecular weight generally have the same strength of London dispersion forces
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When two molecules are of different molecular weights then, which forces determine the the molecule with the stronger intermolecular force?
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Dispersion forces
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The hydrogen in hydrogen bonds bond with _, _, or _ in their own molecule and in those surrounding,
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O, F, N
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Discuss the strength of hydrogen bonds in relativity to other bonds.
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Hydrogen bonds are stronger than van der waals forces but not as strong as ionic or covalent bonds.
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Why do the hydrogen bonds in water make ice more spaced out and therefore less dense?
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Because the H2O molecules in ice optimize their hydrogen bonding by forming 4 other H bonds with H2O molecules, making them very wide open.
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The resistance of a liquid to its flow is called...
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Viscosity
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The greater a liquid's viscosity,...
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The more slowly it flows
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Viscosity _ with molecular weight, and _ with increasing temperature.
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Increases with molecular weight, decreases with increasing temperature
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A measure of the inward forces an object must overcome to expand the surface area of a liquid is given by...
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Surface tension, and insects on water do not have enough force to break this surface tension.
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The energy required increase the surface area of a liquid a given amount is...
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Surface tension (measured in J/m^2)
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Explain why mercury forms an upward meniscus in a glass tube while water's is downward.
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Because the COhesive forces of mercury are stronger than its ADhesive forces to the glass, so it sticks to itself in the tube. Water, however, has a stronger adhesive force to the glass which overcomes its cohesive forces to itself.
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The rise of liquids up very narrow tubes is called...
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Capillary action
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What is the phase change from a gas directly BACK to a solid called?
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Deposition
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The increased freedom of molecules the increases the average separations of the molecules is made by heat, measured in the...
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Enthalpy of fusion
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T/F: Vapor pressure increases with increasing temperature, until it equals the external pressure over the liquid (usually 1 ATM), at which point it boils.
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True
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The energy required to cause the phase change from a liquid to a gas is called...
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The heat of vaporization
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What is the name if the energy required to turn a solid directly into a gas? How is it found?
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Heat of sublimation; found by adding heats of fusion and vaporization
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When you remove heat from a liquid and cool it below its freezing point without forming a solid, it is called...
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Supercooling
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Explain critical temperature.
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When a gas is in a piston at 100 degrees, it takes a certain amount of pressure to condense it, and when the temperature is raised it takes even more pressure, and at some point the temperature is too great for the pressure to overcome it and the highest temperature at which condensation can occur is the critical temperature, and the pressure that causes this phase change is critical pressure.
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T/F: The weaker the intermolecular forces, the larger the numberif molecules that escape, so the higher the vapor pressure.
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True
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T/F: At a constant temperature the rate of liquid molecules vaporizing into a gas and vice versa is equivalent. So, the VAPOR PRESSURE of a liquid is the pressure exerted by its vapor when the liquid and vapor states are in dynamic equilibrium.
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True (closed container. In an open container, rarely do vapor molecules get turned back into a liquid, which is why water in a bowl evaporates.)
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Liquids that evaporate readily are said to be...
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Volatile
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T/F: Vapor pressure increases nonlinearly with increasing temperature, of course.
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True
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In a phase diagram, the state of the substance beyond the critical point is called the...
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Supercritical fluid
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T/F: The melting point and the freezing point of a substance are the same value but only differ in the direction in which they are going
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True
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How can you tell if an unlabeled phase diagram is water?
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Because the line for its melting point (between a solid and a liquid) will be a negative slope instead of a positive slope because
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Because the triple point of the phase diagram of CO2 is so high, at 1 ATM (regular air pressure), CO2...
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Sublimes
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Which solid is regular and which solid is irregular?
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Crystalline and amorphous, respectively.
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How can crystalline quartz (SiO2) be converted from crystalline to amorphrous?
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When it is melted at extremely high temperatures, some of the covalent bonds are broken, and if it is cooled quickly, then the bonds don't have enough time to reform and an amorphous solid forms.
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What is the building block of a crystalline solid?
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The unit cell
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What is the 3-D array of points called that represents a crystalline solid?
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Crystal lattice
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What are the main 3 types of unit cells and their descriptions?
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Primitive cubic (lattice points only in corners), body-centered cubic (lattice points in corners around one centered lattice point, and face-centered cubic (each face of the lattice-cornered cube has its own lattice point).
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What are the four types of crystalline solids?
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Molecular, covalent-network, ionic, and metallic
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Diamond (C) and quartz (SiO2 are examples of...
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Covalent-Network crystalline solids
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Ar, methane, sucrose, and CO2 (dry ice) are all examples of...
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Molecular crystalline solids
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What are the simples, strong forces between ionic particles?
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Electrostatic attractions, of course
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What are the forces between the particles of metallic crystalline solids?
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Metallic bonds
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What makes molecular solids relatively soft?
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They are only held together by INTERmolecular forces (dipole-dipole, London dispersion, H bonds) and so they are pretty weak.
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What does "packing efficiency" have to do with melting points in molecular solids?
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The better backed the molecule is (with less molecules hanging off), the more energy it requires to undergo a phase change (melting). [in contrast, when both molecules are a liquid, the less compact one will have a higher boiling point bc it has more mass!)
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Why would a molecular crystalline solid with an OH- group on the end have a higher melting and boiling point?
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Because it is capable of forming hydrogen bonds
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What is the difference between molecular crystalline solids and covalent network solids if all the molecules have covalent bonds themselves??!
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Molecular solids have molecules with INTRAmolecular forces holding atoms together with covalent bonds, as do covalent network solids. HOWEVER, the atoms of molecular solids only interact with intermolecular forces, while those of covalent networks actually form hundreds upon hundreds of covalent bonds with EACHOTHER, forming a network. Hence the name.
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What does the strength of ionic bonds in ionic solids depend on?
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The charges of the ions. NaCl (+1, +1) has a much weaker ionic bond than do ions of +2, +2 charge.
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Bonding in which there is an array of positive ions immersed in a sea of delocalized valence electrons is called...
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Metallic bonding
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What is a general rule for the strength of metallic bonding?
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The more valence electrons, the stronger the bond. [the displaced valence electrons probably account for the good head conductbility of metallic crystalline solids]
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NOTES: Why do London dispersion forces last longer at lower temperatures?
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Because the temporary dipole moment lasts longer
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The term "polarizability" is ONLY referring to...
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London dispersion forces and their ability to have a dipole moment
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What is Dr. Kemp's reasoning for why linear molecules have stronger dispersion forces than circular molecules?
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Because they have more surface area
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T/F: The stronger the hydrogen bond, the longer the bond between hydrogen and it's original molecule becomes.
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True
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Why don't hydrogen bonds occur very well at higher temperatures?
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Because the preferred orientation of H bonds (110 to 180) can rarely be achieved at such temperatures (thus H bonding is maximized at freezing temps, which is why ice is so spaced out and thus less dense)
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T/F: Ionic crystalline solids are good conductors and POOR insulators
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True
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Different chemical structures of the same element in the same physical state are called...
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Allotropes
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T/F: Metallic crystalline solid bonds do not have enough electrons to fly valence shells, so one electron is shared by many atoms.
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True
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What does the size of a molecule have to do with viscosity?
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If they are longer and more complex, they will get more tangled up and become more viscous
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"If stress is applied to a system at equilibrium, the system will tend to readjust so that the stress is reduced," is...
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Le Chatelier's Principle
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