Chapter 3 Mastering Biology

the attraction of an atom for the electrons in a covalent bond. Atoms in a molecule attract shared bonding electrons to varying degrees, depending on the element. The more electronegative an atom is, the more strongly it pulls shared electrons toward itself

two atoms that do not have similar electronegativities. When an atom is bonded to a more electronegative atom, the electrons of the bond are not shared equally. This type of bond is called a polar covalent bond. Such bonds vary in their polarity, depending on the relative electronegativity of the two atoms.

Water is an electronegative molecule. Elements, not molecules, can be electronegative. When a hydrogen atom is covalently bonded to an electronegative atom such as oxygen in water, the hydrogen atom has a partial positive charge and the oxygen atom has a partial negative charge, making water a polar molecule. The hydrogen atom is attracted to a different electronegative atom nearby. This attraction between the partial positive charge on the hydrogen atom and the partial negative charge on an electronegative atom is called a hydrogen bond.

All of the listed responses are correct.

that atoms in the molecule have partial charges as a result of unequal sharing of electrons in a covalent bond In the case of water, the oxygen is slightly negative and the hydrogen atoms are slightly positive.

the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule Because oxygen is more electronegative than hydrogen, electrons of the polar bond spend more time closer to the oxygen atom, resulting in a slight negative charge on the oxygen atom and slight positive charges on the hydrogen atoms.

the oxygen atom in one water molecule and a hydrogen atom in another water molecule The slightly negatively charged region of an oxygen atom of one water molecule is attracted to the slightly positively charged region of a hydrogen atom of another water molecule.

Ice floats because it is less dense than liquid water; floating ice insulates water below and provides a habitat for some species. The significant increase in Arctic air temperature over the past 50 years is causing a reduction in sea ice, compromising these beneficial effects of sea ice. The warming that has occurred in the Arctic has significantly affected the seasonal balance between ice and liquid water to the degree that sea ice communities are in danger.

The effects would be drastically worse because the loss of the polar nature of water would greatly reduce its specific heat and its ability to moderate temperature. A loss of the polar nature of water would equate to a loss in the ability to form hydrogen bonds. Breaking hydrogen bonds absorbs energy, which accounts for water's high specific heat and its ability to influence and moderate climate.

is called cohesion, acts to moderate temperature, provides the surface tension that allows small animals to move across a water surface, and helps to keep water moving through the vessels in a tree trunk

All are properties related to hydrogen bonding. The extraordinary qualities of water are emergent properties resulting from hydrogen bonding.

both caused by water's partial charges Two molecules of water are held together by a hydrogen bond formed between the slight positive charge of the hydrogen and the slight negative charge of the oxygen. Water is a very versatile solvent, a quality traced to the polarity of the water molecule.

cohesion Cohesion is a consequence of hydrogen bonding between water molecules.

the clinging of one substance to another substance Adhesion is the attraction of one substance to another.

surface tension Water has a greater surface tension, a measure of how difficult it is to break the surface of a liquid, than most other liquids.

condensing 5 g of steam to liquid water

Systems for temperature regulation would have to be much more efficient. In order for living things to inhabit a wide range of environments, temperature regulation would need to be more efficient for a fluid with a lower specific heat.

the specific heat of that substance The specific heat of a substance is defined as the amount of heat that must be absorbed or lost to change the temperature of 1 g of that substance by 1°C.

Heat of vaporization is the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.

specific heat Because of its high specific heat, water's temperature will change less when it absorbs or loses a given amount of heat. Thus, the oceans can absorb and store a huge amount of heat and release it later when the temperature of the air has droppe

Water's high heat of vaporization results in evaporative cooling because when water evaporates, the surface on which it rests cools down.

a higher boiling point More heat is needed to vaporize 1 g of water than most other liquids.

ice floats. Because water molecules in ice are farther apart than in liquid water, ice is less dense, and therefore, it floats.

Because molecules of polar solvents have a positive and a negative pole, polar solvents are excellent solvents for ions and for other polar materials.

Because it is polar, water's negatively charged oxygen atoms and positively charged hydrogen atoms are attracted to positively and negatively charged ions and molecules. Polar water molecules surround the individual ions or charged molecules, separating and shielding the ions or molecules from one another.

hydrophobic Substances that are nonionic and nonpolar repel water.

hydrophobic For example, the hydrophobic behavior of oil molecules results from a prevalence of nonpolar covalent bonds. Nonpolar molecules do not have an affinity for water or other polar molecules.

In order to perform their function of separating the aqueous solutions outside of cells from the aqueous solutions inside of cells, cell membranes cannot be soluble in water. If cell membranes were hydrophilic, they would break down and dissolve in the presence of water, rendering them useless as a barrier.

stir 342 g of sucrose in water to dissolve the sugar, and then add enough water to bring the total volume of the solution up to 0.5 L Or you could stir 684 g of sucrose in water to dissolve the sugar, and then add enough water to bring the total volume of the solution up to 1 L.

0.092g This would produce a 0.002 M or a 2 mM solution.

a compound that donates hydrogen ions to a solution An acid donates hydrogen ions to a solution.

increase the hydrogen ion concentration and lower the pH Because pH is a negative log, its value is inversely proportional to the hydrogen ion concentration.

HF → H+ + F- Hydrofluoric acid (HF) dissociates into a hydrogen ion and a fluoride ion.

ten times as much The pH scale is a base-10 logarithmic scale. The change from any pH value to the next smaller value represents a tenfold increase in the hydrogen ion concentration.

100 times more H+ Each pH unit change represents a tenfold difference in the hydrogen ion concentration; thus 10 × 10 = 100.

lower the hydrogen ion concentration and increase the pH A substance that reduces the hydrogen ion concentration is a base. Reducing the hydrogen ion concentration increases the pH.

Buffer Buffers are substances that minimize changes in the concentration of hydrogen ions and hydroxide ions in a solution; therefore, buffers maintain a relatively constant pH.

More carbon dioxide causes an increase in carbonic acid (H2CO3), which leads to a decrease in the concentration of carbonate ion (CO32-). As seawater becomes more acidic, carbonate ion concentration decreases. The decrease in the availability of carbonate ion makes it more difficult for marine organisms to secrete calcium carbonate shells.

increases the hydrogen ion concentration in the oceans but decreases the carbonate ion concentration and threatens the livability of the oceans for organisms that produce calcium carbonate shells The absorption of CO2 by the oceans causes an increase in the carbonic acid, and hydrogen ion concentration (lower pH). The extra hydrogen ions bind with the carbonate ion to form bicarbonate. This reduces the amount of carbonate ions available for calcification, the production of calcium carbonate (CaCO3) by many marine organisms, including reef-building corals and animals that build shells.