Chapter 2 — The Chemical Context of Life Flashcards

Vocabulary practice cards reviewing essential chemical concepts, atomic structure, radioisotopes, electron shells, chemical bonding, and reactions from Chapter 2.

Element

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

Compound

A substance consisting of two or more elements in a fixed ratio.

Emergent properties

Compound properties that are different from those of its constituent elements.

Essential elements

About 20–25% of the 92 natural elements that an organism requires to live.

Trace elements

Elements required by an organism in minute quantities.

Atom

The smallest unit of matter that retains an element's properties.

Atomic number ($Z$)

The number of protons in the nucleus of an atom.

Mass number ($A$)

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

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Radioactive isotope

An isotope that spontaneously decays, releasing particles and energy.

Parent isotope

An unstable isotope that undergoes radioactive decay.

Daughter isotope

The isotope produced as a product of radioactive decay.

Half-life

A fixed decay rate or time pattern describing radioactive decay.

Radiometric dating

A technique that uses isotope ratios and half-lives to estimate the age of fossils or rocks.

Background radiation

Natural, generally unavoidable radiation exposure.

Sievert (Sv)

The unit used to measure radiation dose.

Energy

The capacity to cause change.

Potential energy

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

Electron shells

Principal energy levels of an atom with characteristic average distance and energy.

Orbital

A 3D space where an electron is found 90% of the time, holding a maximum of 2 electrons.

Valence electrons

Electrons occupying the outermost shell of an atom.

Lewis dots

Diagrams that show valence electrons around an element symbol.

Chemical bond

An attraction that holds atoms close together.

Covalent bond

The sharing of a pair of valence electrons between two atoms.

Single bond

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

Double bond

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

Ion

An atom or molecule with an electrical charge.

Cation

A positively charged ion.

Anion

A negatively charged ion.

Ionic bond

An attraction between oppositely charged ions.

Octet rule

The tendency of atoms to form ions or bonds to achieve a noble-gas electron configuration.

Salt

An ionic compound, such as $NaCl$, often found as crystals.

Bond energy

The amount of energy required to break a chemical bond.

Bond length

The distance separating the nuclei of adjacent bonded atoms.

Hydrogen bond

An attraction where a hydrogen atom covalently bonded to one electronegative atom is attracted to another electronegative atom.

Van der Waals interactions

Attractions resulting from temporary uneven electron distributions rather than actual chemical bonds.

Chemical reaction

The making and breaking of chemical bonds.

Reactants

The starting molecules in a chemical reaction.

Products

The resulting molecules formed by a chemical reaction.

Chemical equilibrium

The point at which forward and reverse reactions occur at the same rate, maintaining constant relative concentrations of reactants and products.