Questions: Chemical Foundations of Life Flashcards

Flashcards covering atomic structure, chemical bonding, water properties, pH, carbon diversity, functional groups, and biological macromolecules based on lecture transcript notes.

How many chemical elements are currently known, and how many occur naturally versus artificially?

There are 118 known elements, of which 94 occur naturally and 24 have been created artificially in the laboratory.

What subatomic particles determine the atomic mass of an atom, and what is the mass assigned to each?

Protons and neutrons determine the atomic mass, with each assigned a mass of $1$, while electrons have negligible mass.

How do electron orbitals differ between the first energy level and the second energy level of a carbon atom?

The first energy level contains one small spherical orbital holding 2 electrons. The second energy level contains four orbitals (one larger spherical orbital and three dumbbell-shaped orbitals) holding the remaining 4 electrons.

How are elements arranged in the periodic table, and what property is shared by elements in the same vertical column?

Elements are arranged in order of increasing atomic number (number of protons). Elements in the same vertical column (group or family) share the same number of electrons in their outermost shell.

What is the octet rule in chemical bonding?

The octet rule is the tendency of elements to prefer eight electrons in their outermost shell, allowing for the formation of stable molecules.

What distinguishes a polar covalent bond from a nonpolar covalent bond?

A polar covalent bond features unequal sharing of electrons due to differences in electronegativity, while a nonpolar covalent bond features equal or nearly equal sharing of electrons between atoms of similar electronegativity.

What occurs at the atomic level when sodium and chlorine form an ionic bond in sodium chloride ($NaCl$)?

Chlorine strips an electron from sodium due to a large difference in electronegativity, forming a negatively charged chloride ion ($Cl^-$) and a positively charged sodium ion ($Na^+$) that associate via electrostatic attraction.

What changes occur during the chemical reaction $2H_2 + O_2 \rightarrow 2H_2O$?

The covalent bonds in $H_2$ and $O_2$ are broken, and each oxygen atom forms new covalent bonds with two hydrogen atoms to yield two water molecules, conserving the total number of each type of atom while releasing energy.

Which four elements account for approximately $90\%$ of the total dry mass of a human cell, and which is the most abundant?

Carbon ($C$), oxygen ($O$), hydrogen ($H$), and nitrogen ($N$) account for approximately $90\%$ of the total dry mass, with carbon being the most abundant element.

How does a carbon atom form four equivalent hybrid orbitals, and what shape do these orbitals form?

One electron from carbon's outermost spherical orbital moves into an empty dumbbell-shaped orbital, converting into four equivalent hybrid orbitals that point toward the four corners of a three-dimensional tetrahedron.

What are isomers, and what specific example of isomers is described in the text?

Isomers are molecules with the same chemical formula but different structural arrangements, such as the amino acids isoleucine and leucine ($C_6H_{13}O_2N$).

Why is silicon considered unlikely to serve as a chemical basis for life despite having four valence electrons like carbon?

Silicon readily and tightly binds to oxygen to form silicate minerals (over 1000 known on Earth), limiting its capability to build the vast diversity of complex structures formed by carbon.

What defines hydrophilic versus hydrophobic compounds in an aqueous environment?

Hydrophilic compounds are polar and dissolve readily in water, whereas hydrophobic compounds are nonpolar and arrange themselves to minimize contact with water.

What dynamic behavior do hydrogen bonds display in liquid water at room temperature?

Hydrogen bonds in liquid water form transient chains of about 150 molecules that dynamically break and reform with new partner molecules about a trillion times per second.

Why does ice float on liquid water, and how does this affect aquatic environments?

In ice, water molecules form an open crystalline lattice where each molecule is hydrogen-bonded to four others, making ice less dense than liquid water; floating surface ice acts as an insulating barrier that preserves liquid water below for aquatic life.

How high can cohesive forces pull water upward in giant sequoia and coast redwood trees?

Cohesion between water molecules allows water to rise as high as $100\,\text{meters}$ above the ground as water evaporates from leaves.

How is pH defined, and what is the typical physiological pH of human circulating blood?

pH measures proton concentration and is calculated as $\text{pH} = -\log[H^+]$; human circulating blood has a physiological pH of approximately $7.4$.

What are the four main classes of carbon-based biological macromolecules and their core cellular functions?

Proteins (structural support and catalysis), nucleic acids (encoding and transmitting genetic information), carbohydrates (energy source and cell walls), and lipids (cell membranes, energy storage, and signaling).

Which commonly observed functional group in biological molecules is nonpolar?

The methyl group ($-CH_3$) is nonpolar, whereas functional groups like amino, carboxyl, hydroxyl, and phosphate are polar.

What basic components make up an amino acid, and which amino acid lacks a distinct side chain?

An amino acid consists of a central $\alpha$-carbon bonded to an amino group, a carboxyl group, a hydrogen atom, and a side chain (R group). Glycine is the exception because its R group is simply a hydrogen atom.

What type of chemical reaction links amino acids together to form peptide bonds?

A dehydration reaction, where the carboxyl group of one amino acid releases a hydroxyl group ($-OH$) and the amino group of another releases a hydrogen atom ($-H$), releasing a water molecule ($H_2O$) as the covalent bond forms.

What structural differences exist between the sugars and bases of DNA and RNA?

DNA contains deoxyribose (which has a hydrogen atom at the $2'$ carbon) and bases A, T, G, C; RNA contains ribose (which has a hydroxyl group at the $2'$ carbon) and bases A, U, G, C.

How do pyrimidine bases structurally differ from purine bases?

Pyrimidines (cytosine, thymine, uracil) have a single-ring structure, whereas purines (adenine, guanine) have a double-ring structure.

What is the key difference between aldose and ketose monosaccharides?

Aldoses contain an aldehyde group ($-CHO$) at one end, whereas ketoses contain a ketone group ($-CO-$).

Why do saturated fatty acids have higher melting points than unsaturated fatty acids of the same length?

Saturated fatty acids lack double bonds and have straight hydrocarbon chains that pack tightly together, maximizing van der Waals interactions; double bonds in unsaturated fatty acids introduce kinks that disrupt tight packing and lower the melting point.