Chemistry Chapter 12

Front 1

Atomic solid

Back 1

Atomic solids are solids whose composite units are individual atoms. Diamond, iron, and solid xenon are good examples of atomic solids.

Front 2

Boiling point.

Back 2

the temp at which the vapor pressure of a liquid is equal to the pressure above it.

Front 3

condensation

Back 3

condensation is the opposite of evaporation. It is an exothermic reaction--heat is released when a gas condenses to a liquid.

Front 4

Covalent atomic solids

Back 4

Covalent atomic solids such as diamond, are held together by covalent bonds. In diamoinds each carbon atom forms 4 covalent bonds to 4 other carbon atoms in a tetrahedral geometry. They have a high melting point.

Front 5

Dipole-dipole force

Back 5

This exists in all polar molecules. Polar molecules have permanent dipoles that interact with the permanent dipoles of neighboring molecules. The positive end of one dipole force is attracted to the negative end of another. This attraction is the dipole dipole force. Polar molecules have higher melting and boliing points than nonpolar of similar molar mass.

Front 6

Dispersion force

Back 6

The default intermolecular force present in all molecules and atoms is dispersion force. These are caused by fluctuations in the electron distribution within molecules or atoms. the dipoles are responsible for the dispersion force constantly appearing and disappearing in response to fluctuations in molecular clouds.

Front 7

Dynamic equilibrium

Back 7

At the point where the rates of condensation and evaporation become equal, dynamic equilibrium is reached and the number of gaseous water molecules above the liquid remains constant.

Front 8

evaporation

Back 8

Evaporation is endothermic, heat is absorbed when a liquid is converted into a gas because energy is required to break a molecule away from the rest of the liquid. As the water evaporates the fastest moving molecules break away leaving the slowest moving ones behind

Front 9

Heat of fusion

Back 9

The amount of heat required to melt 1 mol of a substance is called the heat of fusion.

Front 10

Hydrogen bond

Back 10

Polar molecules containing hydrogen atoms directly bonded to fluorine, oxygen, or nitrogen exhibit an additional intermolecular force called a hydrogen bond. It is a sort of super dipole-dipole force. the large electronegativity difference between hydrogen and these electronegative elements, as well as the small size of these atoms gives rise to a strong attraction.

Front 11

instantaneous dipole

Back 11

The fleeting charge separation is an instantaneous dipole. an instantaneous dipole on one helium atom induces an instantaneous dipole on its neighboring atoms because the positive aend of the instantaneous dipole attracts electrons in the neighboring atoms. This constantlyu appears and dsappears in response to fluctuations in electron clouds.

Front 12

Intermolecular forces

Back 12

Attractive forces that exist between molecules.

Front 13

ionic solid.

Back 13

Ionic solids are solids whose composite units are formula units. The smallest electrically neutral collection of cations and anions that compose the compound. NaCl, table salt and CaF2, calcium flouride are good examples of ionic solids. They are held together by electrostatic attractions between the cations and anions. The forces are actual ionic bonds. Since ionic bonds are much stronger than any of the intermolecular bonds ionic solids have higher meltiong points than molecular solids.

Front 14

Melting point

Back 14

At the melting point, atoms and molecules have enough thermal energy to overcome the intermolecular forces that hold them at their stationary points, the the solid turns into a liquid.

Front 15

Metallic atomic solids

Back 15

Such as iron, have variable melting points, they are held together by metallic bonds that consist of positively charged ions in a sea of electrons. These bonds are of various strength.

Front 16

Miscibility

Back 16

The ability to mix without separating into two phases. in general polar liquids are miscible with other polar liquids byt are not miscible with nonpolar liquids. Example water, polar is not miscible with pentane a on polar liquid.

Front 17

Molecular solids

Back 17

Solids whose composite units are molecules. Ice and dry ice are examples of molecular solids. They are held together by intermolecular forces--dispersion, dipole dipole, and Hydrogen bonding.

Front 18

Nonbonding molecular solid

Back 18

Such as solid Xenon held together by relatively weak dispersion forces. Xenon atoms have stable electron configurations and therefore do not form covalent bonds with each other so they have a very low melting point.

Front 19

nonvolatile

Back 19

liquid that do not vaporize easily.

Front 20

normal boiling point

Back 20

water's normal boiling point is its boiling point at a pressure of 1 atm.

Front 21

Sublimation

Back 21

A physical change in which a substance is converted from its solid form directly to its gaseous form. When this happens molecules leave the surface of the solid where they are held less tightly than in the interior and become gaseous.

Front 22

Surface tension

Back 22

The tendency of liquids to minimize their surface area. This tendency causes liquids to have a sort of "skin" that resists penetration. This is why a paper clip will float on water.

Front 23

Thermal energy

Back 23

The molecules and atoms that compose matter are in constant random motion that increases with increasing temp. The energy associated with this motion is called thermal energy. The weaker the intermolecular forces relative to thermal energy, the more likely the sample will be gaseous.

Front 24

vapor pressure

Back 24

The partial pressure of a gas in dynamic equilirbium with its liquid.

Front 25

viscoscity

Back 25

The resistance of a liquid to flow. Viscoscity is greater in substances with stronger intermolecular forces because molecules can't move around each other as freely, hindering flow. Example--maple syrup.

Front 26

volatile

Back 26

liquids that evaporate easily.

Front 27

Explain what causes a substance to taste bitter

Back 27

The bitter taste is due to the interaction of molecules with receptors on the surface of specialized cells on the tongue.

Front 28

Why are intermolecular forces important?

Back 28

Because they allow us to taste and also help us determine shapes of protein molecules. They are also central to DNA.

Front 29

What is the determines whether a substance is a solid, liquid, or a gas?

Back 29

The magnituted of intermolecular forces relative to the amount of thermal energy in the sample determines the state of the matter.

Front 30

What are the properties of liquids?

Back 30

high densities in comparison to gases, indefinite shape, they assume the shape of their container, and definite volume; they are not easily compressed.

Front 31

Properties of solids

Back 31

high densities in comparison to gases, definite shape; they don't assume the shape of their container, definite volume; they are not easily compressed, may be crystalline ordered or amorphous (disordered).

Front 32

Explain the properties of solids in terms of the molecules or atoms that compose them.

Back 32

Properties of solids explained:
a. Solids have high densities in comparison to gases because the solid particles are in close contact, whereas gas particles are not.
b. Solids have definite shapes. The particles of a solid are in fixed positions.
c. Solids have a definite volume. The particcles of a solid are in close contact.
d. Solids may be crystalline or amorphus A crystalline solid is a well ordered three dimensional array of solid particles.

Front 33

What is the difference between a crystalline solid and an amorphous solid?

Back 33

Crystalline--atoms or molecules that compose them arrange themselves in a well ordered three dimensional array or amorphous in which the atoms or molecules that compose them have no long range order.

Front 34

What iss surface tension? How does it depend on intermolecular forces?

Back 34

Surface tension is the tendency of liquids to minimize their surface area. Molecules at teh surface have few neighbors to interact with via intermolecular forces.

Front 35

What is evaporation? Condensation?

Back 35

Evaporation is a physical change in which a substance is converted from its liquid form to its gaseous form. Condensation is a physical change in which a substance is converted from its gaseous form to its liquid form.

Front 36

Explain the difference between evaporation below the boiling point of a liquid and evaporation at the boiling point of a liquid.

Back 36

Evaporation below the boiling point occurs because molecules on the surface of the liquid experience fewer attractions to the neighboring molecules and can therefore break away. At the boiling point, evaporation occurs faster because more of the molecules have sufficient therefaster because more of the molecules have sufficient thermal energy to break away.

Front 37

cetone evaporates more quickly than water at room temp. What can you say about the relative strength of the intermolecular forces i nthe two compounds? Which is more volatile?

Back 37

Acetone has weaker intermolecular forces than water. Acetone is more volatile than water.

Front 38

How is the vapor pressure of a substance defined? How does it depend on temp and strength of intermolecular forces?

Back 38

VApor pressure is the partial pressure of a gas in dynamic equilibrium with its liquid. It increases with increasing temp, and it also increases with decreasing strength of intermolecular forces.

Front 39

Explain why a steam burn from gaseous water at 100 degrees C is worse than a water burn involving the same amount of liquid water at 100 degrees C

Back 39

A steam burn is worse than a water burn at the same temp because when the steam condenses on the skin it releases large amounts of additional heat.

Front 40

Explain why simply placing a cup of water in a small ice chest (without a refrigeration mechanism) initially at -5 degrees C will NOT result in the freezing of the cup of water.

Back 40

As teh first molecules freeze, they release heat, making it harder for other molecules to freeze without the aid of a refrigeration mechanism, which would draw heat out.

Front 41

Is the melting of ice endothermic or exothermic? What is the sign of change in H for the melting of ice? For the freezing of water?

Back 41

The melting of ice is endothermic change in h for melting is positive. Change in H for freezing is negative.

Front 42

What are dispersion forces? What can you say about the strength of dispersion forces as a function of molar mass?

Back 42

Dispersion forces are the default intermolecular force present in all molecules and atoms. Dispersion forces are caused by fluctuations in the electron distribution within molecules or atoms. they are the weakest type of intermolecular bonds and increase with increasing molar mass.

Front 43

What are dipole dipole forces? How can you tell whether a compound has dipole dipole forces?

Back 43

The positive end of one dipole is attracted to the negative end of another this is the dipole dipole force. If the molecule is polar there are dipole dipole forces.

Front 44

What is hydrogen bonding? How can you tell if a compound has hydrogen bonding?

Back 44

Hydrogen bonding is an intermolecular force and a sort of super dipole dipole force. Hydrogen bonding occurs in compounds containing hydrogen atoms bonded directly to flourine, oxygen or nitrogen.

Front 45

What can you say about the melting points of molecular solids relative to those of other tyoes of solids.

Back 45

Molecular solids have a moderately low melting point relative to other types of types of solidsl however, strong molecular forces can increase their melting points relative to each other.

Front 46

in what ways is water unique?

Back 46

Water is unique because it has a low molar mass, yet it is still liquid at room temp and has a relatively high boiling point. Unlike other substances which contract when they freeze, water expands.