Chapter 7 :States of Matter and Their Attractive Forces: Gas Laws, Solubility, and Applications to the Cell Membrane (7.1-7.5)

CHEM 109: General, Organic, and Biological Chemistry

Gases and Pressure base on

Pressure, temperature, volume, moles.

To illustrare the concept of pressure,

imagine an oral medicine syringe with no needle attached.
- If the plunger of the syringe is drawn all the way out, the syringe fills with
air.
- If you place your finger firmly over the open tip of the syringe and depress the plunger, the sample of air is "squeezed."
- The particles of a gas are usually far apart; a sample of gas is mostly empty space.
- When the air in the syringe is squeezed, the space between the particles
is decreased and the particles of air are forced closer together.

Pressure

Is a force exerted against a given area.

Air pressure is often measured in the unit

Atmosphere (atm).

The SI unit of pressure is the

Pascal (Pa).

Pounds per square inch (psi)

measures pressure as the force (measured in pounds) applied to an area of 1 square inch. The pressure of the atmosphere at sea level is about 14.7 psi.

The unit of millimeters of mercury (mmHg)

Comes from the mercury barometer which measures the pressure of the earth's atmosphere. The unit mmHg is used when measuring blood pressure. (120 over 80)

If the tube is long enough, a column of
mercury

760 millimeter high (29.92 inch) will
remain inside the tube at sea level.

All gases, such as oxygen gas (O2), nitrogen gas (N2),
carbon dioxide gas (CO2), and other gases, behave

similarly.

The kinetic molecular theory of gases explains the

unique
behaviors of gases.

A gas that perfectly adheres to the kinetic molecular theory of gases is said to be

an ideal gas.

The assumptions of the kinetic molecular theory:

-Gas particles are far apart from each other; most of the volume of a gas is empty space.
-Gas particles are in constant, random motion, having a range of speeds.
-Gas particles have no attractive forces between them. -Gas particles are moving and therefore have kinetic energy. This energy is directly proportional to the absolute temperature.
-Gas particles move more quickly at higher temperatures.

Boyle's Law

Pressure and Volume— pressure increases, decreases the volume. Pressure decreases, increase in volume.

Boyle discovered that that when
the pressure on a gas was
doubled, the volume of the
gas was

reduced to half of its
initial volume.

Boyle found that

the volume of a fixed amount of gas at
constant temperature is inversely proportional to the
pressure.

Boyle's Law and Breathing

-When you breathe in, the muscles of your rib cage and your diaphragm contract to cause the volume of your chest cavity to increase. The air pressure inside your lungs decreases.
-The higher pressure of the atmosphere causes air to rush into your lungs to equalize the internal and external pressures.
-When the muscles relax, the volume of your chest cavity
decreases, increasing the pressure in your lungs, and air
flows out to the lower pressure (atmosphere).
-Breathing is an everyday application

Charles found that if the pressure and amount of a gas are not allowed to change, the volume of the gas is

directly proportional to its absolute temperature. When the absolute temperature of a gas is doubled, the volume of the gas is also doubled.

Charles's law states that

the volume of a fixed amount of gas at
constant pressure is directly proportional to its absolute
temperature.

Gay-Lussac's Law

-This law can be used to determine what will happen to a
sample of gas of known pressure and temperature if we
make changes to either pressure or temperature.
-When the temperature increases, the gas particles move
faster and hit the walls of their container more frequently,
increasing the pressure.

Charles's, Boyle's, and Gay-Lussac's laws can be
combined since

pressure, volume, and temperature hold
the same relationship even if all three change for the
same amount of gas.

The Combined Gas Law

Temperature, Pressure, and Volume

Knowing the ideal gas law,

PV = n R T, can assist in remembering all the previously noted gas laws.
-If the number of moles of gas present, n, is held constant, and R is the ideal gas constant, the ideal gas law becomes PV/NT=constant(R)

Changes of state

As a substance is heated, the particles begin to move faster and the interactions between them become less important.
-These include freezing and melting (between liquids and
solids), evaporation and condensation (between liquids
and gases), and sublimation and deposition (between
solids and gases).

A physical equilibrium is reached.

In a closed container, some water molecules
become water vapor.

The pressure of the molecules above the
liquid is called

vapor pressure.
-Every substance has a characteristic vapor pressure, which varies with temperature.
-The boiling point is the temperature at which
the vapor pressure of the liquid equals the
atmospheric pressure.
-stronger attraction forces, vapor less

During boiling, all the molecules in a liquid must have enough

energy to push back the gas molecules at the surface of the liquid, allowing gas molecules of the liquid to escape.

Each liquid molecule must also overcome the attractive forces to the other neighboring molecules and move into the gas phase as

a single molecule.

When the boiling point is reached, the molecules have enough

energy to change from a liquid to a gas.
-The boiling point is the temperature at which the vapor pressure of the liquid equals the atmospheric pressure.

We can predict the vapor pressure and boiling point of one molecule versus another by

examining the attractive forces present.

Attractive forces are caused by the

attraction of an electron-rich area of one compound to an electron-poor area of another compound.

If the attraction is between two molecules, it is called an

intermolecular force.

Stronger attractive forces predict

higher boiling points and lower vapor pressures at a given temperature.

Weakest to Strongest attractive forces

London forces
Dipole-dipole
Hydrogen bonding
Ion-dipole
Ionic attraction

London forces

These attractive forces occur momentarily between all molecules when electrons become unevenly distributed over a molecule's surface. Weakest, don't last long.
-When this happens, the partially positive side of this temporary dipole attracts the electrons of the second molecule, creating an attraction between these two molecules and inducing a temporary dipole in the
second molecule.
-hold cell membranes together.

While all compounds exhibit London forces, these forces are

significant only in the case of nonpolar molecules because London forces are the only attractive force in which nonpolar molecules participate.

The terms induced dipole and dispersion force describe the same attractive force as

London forces. (All molecules have London forces, only invade of non polar)

Such molecules have a permanent dipole.

Polar molecules have a permanently uneven distribution of electrons caused by electronegativity differences in the atoms that make up the molecules.

This type of attraction involves the interaction of two dipoles and is called

a dipole-dipole attraction. Because the dipole in these molecules does not come and go, the
attraction of the partially positive end of one molecule for the partially negative end of another molecule is stronger than London forces. Molecules with permanent dipoles also have London forces, but they are
negligible.

hydrogen bonding

involves a polarized hydrogen (hydrogen in a polar
bond) and is much stronger than other dipole-dipole forces.
- requires the interaction of a donor hydrogen and an acceptor pair of electrons. Water can act as both donor and acceptor.
-holds a D N A double helix in its twist.

Hydrogen-bond donor

A molecule with a hydrogen atom covalently bonded to an oxygen, nitrogen, or fluorine (O, N, or F)

hydrogen-bond acceptor

A molecule with a nonbonding (lone) pair of electrons on an
oxygen, nitrogen, or fluorine (O, N, or F)

The high electronegativity of O,
N and F polarizes the

hydrogen atom of the donor,
giving the hydrogen a high
partial positive charge

The partial positive strongly
attracts the

high partial
negative charge
centered on the nonbonding
electron pair of the O, N or F
acceptor.

Hydrogen bonds can occur between the same molecules,

between two different molecules, or even between different parts of the same molecule.

The ion-dipole attraction

occurs between ionic charges like
those found in salt and polar molecules such as water. -are an important attractive force often
seen in biological systems. This attractive force is stronger than hydrogen bonding.

When oppositely charged ions attract each other, an

ionic attraction exists.

An ionic attraction is the strongest

attractive force.

Ionic attractions are sometimes called

salt bridges.

The organic functional groups carboxylate and protonated amine are found in the

amino acids that form proteins and can form salt bridges when they come into contact with each other.

Because alkanes are nonpolar, the only attractive force present is

London forces.

A molecule with a larger surface area has more

surface contact and more electrons to disturb.

Straight-chain alkanes with more carbons have stronger

attractions between molecules.

Predicting Vapor Pressure and Boiling Points for Alkanes

-The molecules of branched alkanes have less surface contact than do the straight+chain molecules.
-The more contact between two molecules, the greater the attraction of London forces between them.

For alkanes with the same
number of carbon atoms,

straight-chain alkanes have
higher boiling points and
lower vapor pressures than
do branched alkanes.

Melting points follow the same trends as

boiling points. The stronger and more numerous the forces between
molecules, the higher the melting point.

Nonpolar Molecules

The greater the surface area, the lower the vapor pressure and the higher the boiling or melting point

Similar-Sized Molecules, Different Attractive Forces

The stronger the attractive forces, the lower the vapor pressure and the higher the boiling or melting point.

Molecules with Same Attractive Forces

The stronger and more numerous the attractive forces, the lower the vapor pressure and the higher the boiling or melting point.

The attractive forces discussed in this section are used
extensively in nature to

hold biological molecules together.

Cellulose molecules are held tightly together through

hydrogen bonding between neighboring molecules.

Protein structures are held together by

combinations of all the attractive forces discussed.

The maximum amount of a substance that can dissolve in a specified amount of water at a given temperature defines a

substance's solubility in water.

The golden rule of solubility-like dissolves like-means that

molecules that are similar will dissolve in each other. (The "similarity" here relates to whether the molecules are polar or nonpolar.)

Molecules that have similar polarity and participate in the
same types of attractive forces will

dissolve each other.

Hydrophilic

means water-loving, referring to substances that are
soluble in water.

These terms are only used when discussing solubility in water.

Hydrophilic and Hydrophobic

Hydrophobic

means water-hating, referring to substances that
are not soluble in water.

As nonpolar compounds, oils are

attracted to neighboring molecules
through London forces.

Water is a

polar molecule and interacts with other substances through dipole-dipole, hydrogen bonding, and ion-dipole attractions.

The attractions among the water molecules are much greater than the

attraction between a water molecule and an oil molecule. (Because oil and water do not share attractive forces with each other, they are not soluble in each other.)

The hydroxyl groups of sucrose
make it a

polar compound and give it the ability to interact with water through dipole-dipole and hydrogen-bonding interactions. Because table sugar and water are both polar and share these attractive forces, table sugar is
an organic compound that is soluble in water.

hydration

Individual ion-dipole attractions are not stronger than an ionic bond, but when multiple water molecules interact with an ion, the sum of these attractive forces is greater
than the strength of the ionic bonds.

About 85% of all drugs are administered orally to be

absorbed in the digestive tract, so these drugs must be
soluble in water.

More than 40% of new chemicals discovered by the
pharmaceutical industry as potential therapeutic agents
are

insoluble in water.

Pharmaceutical companies often try to create molecules
than have

an amine or carboxylic acid in them so that at
the pH of the body, a charged form is present, increasing
the molecule's solubility in water.

Creating a charged form of a molecule is readily done in the lab by

reacting molecules like pseudoephedrine (a nasal
decongestant) with HCl. This adds a proton to the amine
group, which is easily hydrated in water

Fatty acids are mostly hydrocarbons but contain a

carboxylic acid group

Despite the presence of a carboxylic acid group, these compounds behave

similarly to nonpolar alkanes.

The nonpolar part of the fatty acid is so much larger than

the polar carboxylic acid group that it dominates the character of the compound, making fatty acids mainly nonpolar.

amphipathic (from the Greek amphi meaning "both" and pathic meaning "condition").

Molecules like fatty acids(not water soluble, turn to salt to make soluble) that have both polar and nonpolar parts

Soaps are composed of

fatty acids that have been converted to salts.
-are ionic because they contain the carboxylate
(hydrogen removed) form of the functional group at one
end.
-are not soluble in
water because of the large
nonpolar tails present.

The nonpolar tails are

hydrophobic and will be
excluded from the water,
associating with each other
through London Forces.

Fatty acid salts have

long nonpolar hydrocarbon tails and
extremely polar (ionic) heads, so they are amphipathic.

The hydrophilic ionic heads
interact with the

water mainly through ion-dipole forces.

Micelle

the water interacts only with the ionic heads, the
tails associate with each other, creating the core of a
spherical structure.
-The polar heads form the shell.
- form because the ion-dipole and hydrogen-bonding
attractions between water molecules and the ionic heads
are stronger than (and preferred to) water interactions with the hydrocarbon tails.

Based on the golden rule, greasy dirt is

not soluble in water.
-When skin or clothing with a greasy dirt stain is washed with soapy water, the stain is attracted to the nonpolar hydrocarbon tails of the soap and is dissolved in the interior of the micelle formed by the soap
molecules.
-Because the surface of the micelle is covered with the ionic head groups, the entire micelle with the greasy stain molecules inside is soluble in water and is washed down the drain.

Amphipathic compounds such as soaps are called

emulsifiers because they allow nonpolar and polar compounds to be suspended in the same mixture.

Fats, including steak, lard and butter are

derived from animals.

Oils, like those from corn, soybeans, and peanuts are

derived from plants.

Both fats and oils belong to a class of hydrolyzable lipids
called

triglyercerides.

Determining a fat versus an oil is as simple as examining the physical state of the triglycerides at room temperature

-oils are liquids and fats are solids

Compare the hydrocarbon tails of a fat
molecule and an oil molecule.

-In the fat, the three hydrocarbon tails
have mainly saturated carbon-carbon
bonds.
-The oil has many unsaturated cis carbon-
carbon double bonds in the hydrocarbon tail.

In the ball-and-stick model of the fat, notice that the tails are physically close to each other.

-This proximity creates disturbances in the electron
distribution around each of the tails as they interact with
each other.
-These disturbances result in London forces - the tails of the fat are attracted to each other.
-These mostly straight-chain tails allow for many surface
contacts, which increases the attractions between the tails and restricts the molecular motion, allowing the molecules to form a solid or a semisolid.

Look at the ball-and-stick model of the oil molecule. It has many unsaturated cis carbon-carbon double bonds in the hydrocarbon tails, making it

polyunsaturated.

Notice how the cis double bonds in the tails of the oil creates kinks in the otherwise straight hydrocarbon chain.

-The kinked tails interact less with each other through London forces because the tails of the unsaturated oil cannot stack together as closely as those in the fat
can.
-Less London force attractions means that the hydrocarbon chains in the oil move
more freely.
-The greater molecular motion among the hydrocarbon tails in an oil does not
allow enough stacking of the tails for a solid to form at room temperature.

The main structural components of cell membranes are called

phospholipids.
-have a glycerol backbone with fatty acids linked to it
through an ester bond.
-have only two fatty acids on their glycerol
backbone. The third OH group of the glycerol is bonded to a phosphate-containing group.

The phosphate-containing group is

ionic (polar). The fatty-acid tails are nonpolar.

There are many different phospholipids, but they all share this similar structure:

-a glycerol backbone with two nonpolar fatty
acid tails and a polar phosphate-containing head.
-The two tails of the phospholipid affect the overall shape of the molecule.
-Phospholipids have a cylindrical shape with a much larger head group, which hinders their ability to form micelles.

A cell membrane composed of phospholipids cannot exist as a single layer. Instead, the phospholipids form a double layer called p

a bilayer.
-The polar heads are directed out into the surrounding aqueous environment and into the aqueous interior of the cell.
-This arrangement leaves the hydrophobic tails of both layers directed toward each other, creating a nonpolar interior region.
The phospholipid bilayer is the structural foundation for a cell's membrane.

Protein molecules can

span the bilayer (integral membrane
proteins) or associate with one hydrophilic surface of the bilayer (peripheral membrane proteins).