AP Biology Chapter 2: The Chemical Context of Life

Vocabulary flashcards covering chemical concepts, atomic structure, bonding, reactions, and the properties of water as outlined in AP Biology Chapter 2.

Matter

Anything that takes up space and has mass.

Element

A substance that cannot be broken down to other substances by chemical reactions.

Compound

A substance consisting of two or more different elements combined in a fixed ratio, exhibiting emergent properties.

Essential Elements

The elements that an organism needs to live a healthy life and reproduce, with Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N) making up approximately $96\%$ of living matter.

Trace Elements

Elements required by an organism in only minute quantities, such as Iodine or Iron.

Iodine

A trace element required for the normal functioning of the thyroid gland; a deficiency can cause a goiter.

Emergent Properties (in chemistry)

The phenomenon where a compound possesses different physical and chemical characteristics from those of its constituent elements.

Protons

Subatomic particles with a single positive electrical charge, located in the atomic nucleus.

Neutrons

Subatomic particles that are electrically neutral, found in the nucleus; their number is determined by subtracting the atomic number from the mass number.

Electrons

Subatomic particles with a single negative electrical charge, moving around the nucleus and determining chemical behavior.

Atomic Number

The number of protons in the nucleus of an atom, which is unique to each element and determines its identity.

Isotopes

Different atomic forms of the same element that have the same number of protons but a different number of neutrons, resulting in a different atomic mass.

Radioactive Isotope

An isotope in which the nucleus decays spontaneously, giving off detectable particles and energy.

Valence Shell

The outermost electron shell of an atom; atoms with incomplete shells are chemically reactive.

Covalent Bond

A strong chemical bond formed by the sharing of a pair of valence electrons by two atoms.

Electronegativity

The attraction of a particular atom for the electrons of a covalent bond.

Nonpolar Covalent Bond

A bond where electrons are shared equally between two atoms of similar electronegativity.

Polar Covalent Bond

A bond where electrons are shared unequally because one atom is more electronegative than the other.

Ionic Bond

A chemical bond resulting from the attraction between oppositely charged ions (cations and anions).

Hydrogen Bond

A weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule.

van der Waals Interactions

Weak attractions between molecules that occur only when they are very close together, resulting from transient local partial charges.

Chemical Equilibrium

The point at which the forward and reverse reactions occur at the same rate, resulting in stable concentrations of reactants and products.

Photosynthesis Equation

The chemical process represented by $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$.

Polar Molecule

A molecule, such as water ($H_2O$), where the overall charge is unevenly distributed across the structure.

Cohesion

The phenomenon where hydrogen bonds hold water molecules together, helping transport water against gravity in plants.

Surface Tension

A measure of how difficult it is to stretch or break the surface of a liquid, which is high in water due to hydrogen bonding.

Specific Heat

The amount of heat that must be absorbed or lost for $1\,g$ of a substance to change its temperature by $1^{\circ}C$; water has a high value which stabilizes temperatures.

Evaporative Cooling

The process where the surface of an object becomes cooler during evaporation as the hottest molecules leave the liquid phase.

Hydrophilic

Any substance that has an affinity for water; "water-loving".

Hydrophobic

Substances that are nonionic and nonpolar, thereby repelling water; "water-fearing".

Acid

A substance that increases the hydrogen ion ($H^+$) concentration of a solution.

Base

A substance that reduces the hydrogen ion ($H^+$) concentration of a solution.

pH

A measurement defined as the negative logarithm (base $10$) of the hydrogen ion concentration: $pH = -\log[H^+]$.

Neutrality

A solution state at $pH\,7$, where the concentrations of $H^+$ and $OH^-$ are equal.

Buffer

A substance that minimizes changes in the concentrations of $H^+$ and $OH^-$ in a solution by accepting or donating hydrogen ions.

Carbonic Acid-Bicarbonate System

An important buffer system in human blood that shifts in response to changes in $pH$.

Ocean Acidification

The lowering of ocean $pH$ caused by the absorption of excess atmospheric $CO_2$, which harms marine organisms by reducing carbonate ion availability.

Molarity

A measure of solute concentration, defined as the number of moles of solute per liter of solution ($mol\,dm^{-3}$).