Chapter 2: The Chemical Basis of Life I: Atoms, Molecules, and Water

Comprehensive vocabulary flashcards covering atoms, subatomic particles, chemical bonding, water properties, and acid-base buffers from Brooker Biology Chapter 2.

Matter

Anything that has mass and occupies space, existing in three physical states: solid, liquid, or gas.

Atom

The smallest functional unit of matter that forms all chemical substances and cannot be broken down into other substances by ordinary means.

Proton

A positively charged subatomic particle ($+1$) located in the atomic nucleus, possessing a relative mass of $1{,}836$ compared to an electron.

Neutron

An uncharged, neutral subatomic particle ($0$) located in the atomic nucleus, possessing a relative mass of $1{,}839$ compared to an electron.

Electron

A negatively charged subatomic particle ($-1$) found in orbitals surrounding the nucleus, possessing a relative mass of $1$.

Orbital

A cloudlike region surrounding an atomic nucleus where the probability of finding a particular electron is high; each orbital can hold up to $2$ electrons.

Valence Electrons

Electrons located in the outermost electron shell that are available to combine and form chemical bonds with other atoms.

Atomic Number

The number of protons in an atom's nucleus, which distinguishes one element from another and equals the electron count in an atom with no net charge.

Periodic Table

A systematic arrangement of chemical elements organized by atomic number, where rows indicate electron shells and columns indicate the number of valence electrons.

Atomic Mass

A scale indicating an atom's mass relative to other atoms, standardized relative to carbon-12 having an atomic mass of exactly $12$.

Dalton (Da)

A unit of measurement for atomic mass (also called an atomic mass unit or amu), equal to $1/12$ the mass of a carbon atom.

Mole

An amount of any substance containing Avogadro's number of atoms or molecules, weighing in grams exactly equivalent to its atomic or molecular mass.

Isotopes

Multiple forms of a chemical element that share the same number of protons but differ in their number of neutrons.

Radioisotopes

Unstable isotopes that emit radiation as they decay, used in medical diagnostic imaging such as PET scans and in cancer treatments.

Mineral Elements

Essential chemical elements—including $Ca$, $Cl$, $Mg$, $P$, $K$, $Na$, and $S$—that constitute less than $1\%$ of total human body mass.

Trace Elements

Essential chemical elements that make up less than $0.01\%$ of total human body mass, yet are required for normal growth and function.

Molecule

A distinct chemical structure consisting of two or more atoms bonded together.

Compound

Any molecule composed of two or more different chemical elements, possessing properties distinct from its constituent elements.

Covalent Bond

A strong chemical bond formed when atoms share one or more pairs of electrons to fill their unfilled valence shells.

Octet Rule

The chemical principle that many atoms are most stable when their outer electron shell is filled with $8$ electrons (with hydrogen being an exception filled with $2$).

Electronegativity

A measure of the attraction an atom exerts on electrons within a chemical bond.

Polar Covalent Bond

A covalent bond between atoms of differing electronegativity (difference between $0.4$ and $1.8$) where electrons are shared unequally, producing partial electric charges across the bond.

Nonpolar Covalent Bond

A covalent bond formed between atoms with similar electronegativities (difference $< 0.4$) characterized by equal sharing of electrons and no charge difference across the molecule.

Hydrogen Bond

A weak attraction between a partially positive hydrogen atom in one polar molecule and an electronegative atom in another polar molecule.

van der Waals Dispersion Forces

Weak, fleeting electrical attractions between adjacent molecules that arise from temporary, random fluctuations in orbital electron distribution.

Ion

An atom or molecule that has gained or lost one or more electrons, thereby acquiring a net electrical charge.

Cation

An ion with a net positive electrical charge ($+$) formed when an atom loses one or more electrons.

Anion

An ion with a net negative electrical charge ($-$) formed when an atom gains one or more electrons.

Ionic Bond

A chemical bond resulting from the electrostatic attraction between a positively charged cation and a negatively charged anion (electronegativity difference $> 1.8$).

Free Radical

A highly reactive molecule containing an atom with a single, unpaired electron in its outer shell that can steal electrons from other molecules and induce cellular damage.

Antioxidant

A protective compound capable of donating electrons to free radicals without transforming into a highly reactive state itself.

Solute

A substance that dissolves in a liquid to form a solution.

Solvent

The liquid medium in which solute molecules dissolve to create a solution.

Hydrophilic

"Water-loving"; referring to ions and molecules with polar covalent bonds that readily dissolve in water.

Hydrophobic

"Water-fearing"; referring to nonpolar molecules like hydrocarbons and oils that do not dissolve in water.

Amphipathic

"Both loves"; describing molecules possessing both polar/ionized (hydrophilic) and nonpolar (hydrophobic) regions.

Micelle

A spherical aggregate formed in water by amphipathic molecules, orienting polar hydrophilic surfaces outward toward water and nonpolar hydrophobic tails inward.

Molarity

A measure of concentration defined as the number of moles of a solute dissolved in $1\,\text{L}$ of solution.

Heat of Vaporization

The amount of heat energy required to transition a substance from a liquid into a gas (to boil).

Heat of Fusion

The amount of heat energy required to transition a substance from a solid to a liquid state (to melt).

Specific Heat

The quantity of heat energy required to raise the temperature of a substance by $1\,^\circ\text{C}$.

Colligative Properties

Solution properties that depend strictly on the total number of dissolved solute particles rather than their chemical identity, such as freezing point depression and boiling point elevation.

Cohesion

The property whereby molecules of the same type attract one another, such as water molecules binding together to move fluids through plant vessels.

Adhesion

The property whereby unlike molecules attract one another.

Surface Tension

A measure of attraction between molecules at the surface of a liquid, creating an elastic barrier capable of supporting organisms like water striders.

Acid

A substance that releases hydrogen ions ($H^+$) in solution, resulting in a $pH$ value of $6$ or below.

Base

A substance that decreases the $H^+$ concentration of a solution by releasing hydroxide ions ($OH^-$) or binding free $H^+$, resulting in a $pH$ of $8$ or above.

pH

A mathematical scale expressing hydrogen ion concentration, defined by the formula $\text{pH} = -\log_{10}[H^+]$.

Buffer

An acid-base system that maintains a relatively constant $pH$ by shifting equilibrium to release or bind $H^+$ in response to fluctuations.