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How are liquids and solids distinguished from gases
by the presence of substantial attractive forces between particles
Explain attractive forces in: liquids
they are strong enough to hold hte particles in close contact while still letting them slip and slide over one another
Explain attractive forces in:
the forces are so strong that they hold the particles in place and prevent their movement
How do we represent a dipole and what is it?
- an arrow with a cross at one end to indicate the direction of electron displacement
- the point of the arrow represents the negative end of the dipole and the crossed end represents the positive end
- a pair of separated electrical changes
The measure of net molecular poliarity is a quantity called the __. Define it.
- dipole moment
- the magnitude of the charge Q at either end of the molecular dipole times the distance r between the charges: u= Q x r
The largest dipole moment listed in Table 10.1 (see txt p. 348) is __.
the ionic compound NaCl
Atoms are held together by __, but some forces that must be in play between molecules to hold them close together at certain temperatures is called __.
- intramolecular forces
- intermolecular forces
Intermolecular forces as a whole are usually called __. These forces are of several different types, including __, __, and __. In addition, __ operate between ions and molecules. All these intermolecular forces are __ in origin and result form the mutual attraction of __ or the mutual __.
- van der Waals forces
- dipole-dipole forces
- London dispersion forces
- hydrogen bonds
- ion-dipole forces
- unlike charges
- repulsion of like charges
If the particles are ions, then __ charges are present and the ion-ion attractions are so strong they give rise to __.
If the particles are neutral, then what?
only partial charges are present at best, but even so, the attractive forces can be substantial
An __ is the result of electrical interactions between an ion and the partial charges on a polar molecule.
The magnitude of the __ depends on the __, on the __, and on the __.
- interaction energy E
- charge on the ion z
- strength of the dipole as measured by its dipole moment u
- inverse square of hte distance r from the ion to the dipole
Neutral but polar molecules experience __ as the result of electrical interactions among dipoles on neighboring molecules.
The forces can be either __ or __, depending on the __ of the molecules and the __ in a large collection of molecules is a summation of many individual interactions of both types. The forces are generally __, with energies on the order of 3-4kJ/mol and are significant only when?
- dipole-dipole forces
- attractive or repulsive
- net force
- molecules are in close contact
Explain attraction and repulsion of polar molecules.
polar molecules attract one another when they orient with unlike charges close together but repel one another when they orient with like charges together
The more polar hte substance is, the __.
greater the strength of its dipole-dipole interactions
The larger the dipole moment, the __, and the __.
Thus, substances with higher dipole moments genearlly have __.
- stronger the intermolecular forces and hte greater the amount of heat that must be added to overcome those forces
- higher boiling points
All atoms and molecules, regardless of structure, experience __, which result form the motion of electrons.
London dispersion forces
__ are generally small and hteir exact magnitude depends on the ease with which a molecule's electron cloud can be distorted by a nearby electric field, a property called __.
- dispersion forces
A smaller molecule or lighter atom is __ and has __ because it has only a few, tightly held electrons.
- less polarizable
- dispersion forces
A larger molecule or heavier atom is __ and has __because it has many electrons, some of which are less tightly held and are farther from the nucleus.
- more polarizable
- larger dispersion forces
__ is also important in determining the magnitude of the dispersion forces affecting a molecule. Explain.
- more spread-out shapes, which maximize molecular surface area, allow greater contact between molecules and give rise to higher dispersion forces than do more compact shapes, which minimize molecular contact
__ cause water to be a liquid rather than a gas at ordinary temperatures.
True or False:
Hydrogen bonds are very minutely polar.
- hydrogen bonds are highly polar, with a partial positive charge on the hydrogen and a partial negative charge on the electronegative atom
What doesn't hydrogen atoms have?
no core electrons to shield its nucleus, and it has a small size so it can be approached closely by other molecules
What is viscosity related to?
the ease with which individual molecules move around in the liquid and thus to the intermolecualr forces present
What is surface tension caused by?
- the difference in intermolecular forces experienced by molecules at the surface of a liquid and those experienced by molecules in the interior
- molecules at the surface feel attractive forces only on one side and are pulled in toward the liquid, while molecules in the interior are surrounded and are pulled equally in all directions
Under what conditions is surface tension higher?
in liquids that have stronger intermolecular forces
Surface tension adn viscotiy are __ because molecules at higher temperatures have more __ to counteract the attractive forces holding them together.
- kinetic energy
Process in which the physical form but not the chemical identity of a substance changes is called __.
- phase change
- changes of state
Every phase change has associated with it a __.
What are the two components of free energy.
- enthalpy (heat flow associated with making or breaking hte intermolecular attractions that hold liquids and solids together
- entropy (differnece in molecular randomness between various phases
__ are more random and have more __ than liquids, which in turn are more random and have more __ than __.
- entropy solids
Melting, sublimation, and vaporization all involve a change from __. They also all __. Thus the deltaS and deltaH are __ for these phase changes.
- aless random phse to a more random one
- absorb heat energy to overcome the intermolecular forces holding particles together
By contrast, freezing, deposition, and condensation all involve a change from __ and all __. Thus, both deltaS and deltaH have __ values.
- a more random phase to a less random one
- release heat energy as intermolecular attractions increase to hold particles more tightly together
Why are deltaH and deltaS larger for the liquid--> vapor change than for the solid--> liquid change?
because many more intermolecular attractions need to be overcome and much more randomness is gained in the change of liquid to vapor
The results of continuously adding heat to a substance can be displayed on a __.
At the melting point and boiling point, what occurs?
the two phases coexist in equilibrium as molecules break free from the phase and enter the next
At equilibrium and at a constant temperature, the pressure increase has a constant value called the __ of a liquid.
Evaporation and vapor pressure are both explained on a molecular level by the __.
As more and more molecules pass from the liquid to the vapor, the chances increase that __ will cause __.
- random motion
- some of them to return occasionally to the liquid
Ultimately, the number of molecules returning to the liquid and the number escaping become __, at which point a __ exists.
Although __ are constantly passing back and forth from one phase to the other, the __ of molecules in both liquid adn vapor phases remain __.
- total numbers
The numerical value of a liquid's vapor pressure depends on what?
the magnitude of the intermolecular forces present and on the temperature
The smaller the intermolecular forces, the __. Why?
The higher the temperature, the __. Why?
- higher the vapor pressure, because loosely held molecules escape more easily
- higher vapor pressure is, because a larger fraction of molecules have sufficient kinetic energy to escape
Although vapor pressure and temperature are not linear, a linear relationship is found when __.
the natural logarithm of the vapor pressure , ln Pvap, is plotted against inverse of Kelvin, called the Clausius Clapeyron equation
What happens when the vapor pressure of a liquid rises to the point where it becomes equal to the external pressure?
the liqui boils and changes into vvapor
The most fundamental distinction between kinds of solids is that some are __ and others __
What are crystalline solids?
those whose constituent particles--atoms, ions, or molecules-- have an ordered arrangement extending over a long range
those whose constiuent particles are randomly arranged and have no ordered long-range structure
What are the classifications of crystalline solids?
- covalent network
solids whose constituent particles are ions
thsoe whose constiuent particles are molecuels ehld together by intermolecular forces
Covalent network solids
those whose atoms are linked togethr by covalent bonds into a giant 3D array
consists of large arrays of atoms, but their crystals have metallic properties like electrical conductivity
brittle, hard, high melting
solf, low-melting, nonconducting
variable hardness and melting point, conducting
When does diffraction of electromagnetic radiation occur?
when a bean is scattered by an object containing regularly spaced lines or points
What is diffraction due to?
interference between two waves passing through the same region of space at the same time
if the waves are in-phase, peak to peak and trough to trough, the interference is constructive and the combined wave is increased in intensity
If the waves are desetructive...
if the waves are out-of-phase, the interference is destructive and the wave is canceled
simple cubic packing
orderly rows and stacks with spheres in one layer sitting directly on top of those in the previous layer, each sphere is touched by six neighbors, giving a coordination number of 6
body-centered cubic packing
- the spheres in layer a are separated slightly and the spheres in layer b are offset so they fit into the depressions between atoms in layer a; the third layer is the same as hte first
- coordination number of eight
Hexagonal closest-packed arrangement
- two alternating layers, a-b-a-b
- each layer has a heaxagonal arrangement of touching spheres, which are offset so that spheres in a b layer fit into small triangular depressions between spheres in an a layer
- coordination number of 12
Cubic closest packed arrangement
- three alternating layers
- ab layers are identical to those in the hexagonal closest-packed arrangment
- third layer is offset from both a and b layers
- coordination number of 12
How many unit cell geometries occur in crystalline solids?
- all are parallelepipeds--6 sided geometric solids whose faces are parallelograms
Three kinds of cubic uit cells
- primitive cubic
- body centered cubic
- face centered cubic
an atom at each of its eight corners, where its shared with seven neighboring cubes that come together at some point
Body centered cubic unit cell
eight corner atoms plus an additional atom in the center of hte cube
Face centered cubic unit cell
eight corner atoms plus an additional atom in the center of each of its six faces, where it is shared with one other neighboring cube
How do simple ionic solids differ from metals?
the spheres are not all the same size--anions have larger radii than cations, leading ionic solids to adopt a variety of different unit cells depending on size and charge of the ions
TRUE OR FALSE:
It's necessary that the unit cell of an ionic substance be electrically neutral, with equal numbers of positive and negative charges
Carbon exists in more than forty known structural forms, or __, several of whicha re __but most of which are __.
__, the most common allotrope of carbon and the most stable under normal conditions, is a crystalline covalent network solid that consists of two-dimensional sheets of fused six-membered rings.
Tje __ form of elemental carbon is a covalent network solid in which each carbon atom is sp3-hybridized and is bonded with tetrahedral geometry to four other carbons.
A third crystalline allotrope of carbon called __ was discovered as a constituent of soot.
Closely related to both graphite and fullerene are a group of carbon allotropes called __-- tubular structures madeof repeating six membered carbon rings
The dramatic difference in properties between CO2 and SiO2 is due primarily to the difference in __ between carbon and silica.
What does a typical phase diagram show?
which phase is stable at different combinations of pressure and temperature
WHat do points on a phase diagram represent?
pressure/ temperature combos at which they are in equilibrium in a closed system and a direct phase transition between solid ice and gaseous water vapor occurs
What is a triple point?
the solid/ liquid/ gas intersection at which all three phases coexist in equilibrium
A gas at the critical point is under such high pressure, and its molecules are so close together, that it becomes __
- indistinguishable from a liquid
- Same goes for liquid: molecuels are so far apart, they become indistinguishable from a gas--> supercritical fluid that is neither true liquid or true gas