Chapter 2: The Chemical Context of Life

Vocabulary flashcards covering key chemical concepts, subatomic particles, bonding types, and reaction terminology from Chapter 2 of Campbell Biology.

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 elements in a fixed ratio, possessing characteristics different from those of its constituent elements.

Essential Elements

The chemical elements required for life, which make up about $20-25\%$ of the $92$ natural elements.

Trace Elements

Elements required by an organism in only minute quantities, accounting for less than $0.01\%$ of body mass.

Atom

The smallest unit of matter that still retains the chemical properties of an element.

Neutrons

Subatomic particles located in the nucleus that carry no electrical charge.

Protons

Positively charged subatomic particles in the nucleus that determine an atom's identity.

Electrons

Negatively charged subatomic particles that orbit the nucleus and determine an atom's ability to form bonds.

Atomic Number

The number of protons in the nucleus of an atom, unique to each element.

Mass Number

The sum of protons plus neutrons in an atom's nucleus.

Atomic Mass

The total mass of an atom, which can be approximated by its mass number.

Potential Energy

The energy that matter possesses because of its location or structure.

Electron Shell

An energy level representing a discrete state of potential energy for electrons in an atom.

Valence Electrons

Electrons located in the outermost shell of an atom that primarily dictate its chemical behavior.

Valence Shell

The outermost electron shell of an atom.

Orbital

The three-dimensional space where an electron is found $90\%$ of the time.

Chemical Bonds

Attractions that hold atoms close together through the sharing or transfer of valence electrons.

Covalent Bond

A chemical bond formed when two atoms share a pair of valence electrons.

Molecule

Two or more atoms held together by covalent bonds.

Single Bond

A covalent bond formed by the sharing of one pair of valence electrons.

Double Bond

A covalent bond formed by the sharing of two pairs of valence electrons.

Structural Formula

A notation that uses lines to represent covalent bonds between atoms (e.g., $H-H$).

Molecular Formula

An abbreviated representation showing the numbers and types of atoms in a molecule (e.g., $H_2$).

Valence

The bonding capacity of an atom, typically equal to the number of unpaired electrons in its valence shell.

Electronegativity

An atom's attraction for shared electrons in a covalent bond.

Nonpolar Covalent Bond

A covalent bond in which electrons are shared equally between two atoms.

Polar Covalent Bond

A covalent bond in which one atom is more electronegative than the other, resulting in unequal electron sharing and partial positive ($\delta+$) or negative ($\delta-$) charges.

Ion

A charged atom or molecule resulting from a gain or loss of electrons.

Cation

A positively charged ion.

Anion

A negatively charged ion.

Ionic Bond

A chemical bond formed by the electrostatic attraction between a cation and an anion.

Ionic Compounds

Compounds formed by ionic bonds, also known as salts.

Hydrogen Bond

A weak interaction formed when a hydrogen atom covalently bonded to an electronegative atom is attracted to another electronegative atom on a different molecule.

Van der Waals Interactions

Weak attractions between molecules that are close together resulting from transient uneven distributions of electron density.

Reactants

The starting molecules of a chemical reaction.

Products

The final molecules produced by a chemical reaction.

Chemical Equilibrium

The state reached when the forward and reverse chemical reactions occur at the exact same rate, stabilizing relative concentrations of reactants and products.