Chapter 2: Atoms and Molecules - The Chemical Basis of Life

Comprehensive vocabulary flashcards generated directly from Chapter 2 notes covering elements, subatomic particles, chemical bonding, redox reactions, water chemistry, and pH buffers.

Element

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

Trace element

An element required by organisms in only minute amounts, such as iodine, copper, or zinc.

Atom

The smallest portion of an element that retains its unique chemical properties.

Matter

Anything that has mass and takes up space.

Subatomic particles

Tiny components of matter that make up an atom, specifically protons, neutrons, and electrons.

Electron

A subatomic particle that carries a unit of negative electric charge and occupies the space surrounding the atomic nucleus.

Proton

A subatomic particle that carries a unit of positive electric charge and resides within the atomic nucleus.

Neutron

An uncharged subatomic particle located within the atomic nucleus.

Atomic nucleus

The dense central core of an atom formed by a cluster of protons and neutrons.

Atomic number

The fixed number of protons in the atomic nucleus of an atom, which defines the element's identity.

Periodic table

A chart of the chemical elements arranged in order of increasing atomic number.

Atomic mass unit (amu)

A unit of mass (also called a dalton) equal to the approximate mass of a single proton or neutron, roughly $1.7 \times 10^{-24}\,g$.

Atomic mass

The total mass of an atom expressed in amu or daltons, calculated by adding the number of protons and neutrons.

Isotopes

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

Radioisotopes

Unstable isotopes that spontaneously decay to a more stable form, emitting radiation in the process.

Autoradiography

A technique used to detect radioactive decay by exposing photographic film to radiation to produce dark silver grains.

Orbital

A characteristic region of three-dimensional space surrounding an atomic nucleus where an electron is located, containing up to 2 electrons.

Electron shell

A group of electron orbitals with similar energy levels surrounding the nucleus of an atom.

Valence electrons

The most energetic electrons occupying the outermost energy level (valence shell) of an atom.

Chemical compound

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

Molecule

A stable particle consisting of two or more atoms joined together by strong covalent bonds.

Simplest formula

A chemical formula (also called an empirical formula) giving the smallest whole-number ratio of atoms in a compound.

Molecular formula

A chemical formula specifying the actual numbers of each type of atom present in a single molecule.

Structural formula

A chemical formula displaying both the types and numbers of atoms as well as their spatial arrangement in a molecule.

Molecular mass

The sum of the atomic masses of all the component atoms in a single molecule.

Mole (mol)

The amount of an element or compound whose mass in grams is equivalent to its atomic or molecular mass, containing $6.02 \times 10^{23}$ units.

Avogadro's number

The fixed number of units contained in 1 mole of any substance, equal to $6.02 \times 10^{23}$.

Molar solution (1 M)

A solution containing $1\,mol$ of a substance dissolved in a total volume of $1\,L$.

Reactants

The starting substances that enter into and participate in a chemical reaction.

Products

The substances formed as a result of a chemical reaction.

Dynamic equilibrium

A state in a reversible reaction where the forward and reverse reaction rates are equal, resulting in stable concentrations.

Bond energy

The energy necessary to break a chemical bond.

Covalent bond

A strong chemical bond formed when atoms share pairs of valence electrons to complete their outer shells.

Lewis structure

A structural notation that represents the valence electrons of an atom or molecule as dots around chemical symbols.

Orbital hybridization

The process in which valence shell orbitals rearrange when covalent bonds form, determining the overall geometric shape of the molecule.

Electronegativity

A measure of an atom's attraction for shared electrons in chemical bonds.

Nonpolar covalent bond

A covalent bond formed between atoms with similar electronegativities, leading to equal electron sharing.

Polar covalent bond

A covalent bond between atoms that differ in electronegativity, creating partial positive and partial negative charges.

Polar molecule

An electrically neutral molecule with one end having a partial positive charge and the opposite end having a partial negative charge.

Ion

An atom or group of covalently bonded atoms carrying one or more positive or negative electric charges.

Cation

A positively charged ion formed when an atom or group of atoms loses one or more electrons or gains protons.

Anion

A negatively charged ion formed when an atom or group of atoms gains one or more electrons or loses protons.

Ionic bond

A chemical bond formed by the electrical attraction between a positively charged cation and a negatively charged anion.

Ionic compound

A substance composed of cations and anions held together in a lattice structure by ionic bonds.

Solute

A substance that is dissolved in a solvent to form a solution.

Hydration

The process in which dissolved cations and anions are surrounded by the oppositely charged poles of water molecules.

Hydrogen bond

A weak attraction between a hydrogen atom carrying a partial positive charge and an electronegative atom carrying a partial negative charge.

van der Waals interactions

Weak, short-range attractive forces between nonpolar molecules or regions created by temporary electric charge fluctuations.

Redox reaction

An oxidation-reduction reaction in which electrons (and their energy) are transferred from a reducing agent to an oxidizing agent.

Oxidation

A chemical process in which an atom, ion, or molecule loses one or more electrons.

Reduction

A chemical process in which an atom, ion, or molecule gains one or more electrons.

Oxidizing agent

The substance in a redox reaction that accepts electrons and becomes reduced.

Reducing agent

The substance in a redox reaction that donates electrons and becomes oxidized.

Cohesion

The property of like molecules, such as water, sticking to one another due to hydrogen bonding.

Adhesion

The ability of water molecules to stick to different substances, particularly those with polar or charged surfaces.

Capillary action

The tendency of water to rise in narrow tubes against gravity through a combination of adhesion and cohesion.

Surface tension

The strong cohesive force at the surface of a liquid that causes its molecules to crowd together.

Hydrophilic

Describing polar or ionic substances ("water-loving") that readily interact with and dissolve in water.

Hydrophobic

Describing nonpolar substances ("water-fearing") that do not dissolve in water and cluster together.

Hydrophobic interactions

The clustering of nonpolar molecules caused by water molecules excluding them and bonding with one another.

Heat

The total quantity of kinetic energy contained in a sample of a substance.

Temperature

A measure of the average kinetic energy of the particles in a substance.

Heat of vaporization

The amount of heat energy required to transition $1\,g$ of a liquid into the vapor phase.

Calorie (cal)

The amount of heat energy (equivalent to $4.184\,J$) required to raise the temperature of $1\,g$ of water by $1\,^{\circ}\text{C}$.

Evaporative cooling

The reduction in average temperature of a liquid sample as its highest-energy molecules escape into the vapor phase.

Specific heat

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

Acid

A substance that dissociates in water to yield hydrogen ions ($H^+$) and anions, functioning as a proton donor.

Base

A substance that functions as a proton acceptor, often dissociating to yield hydroxide ions ($OH^-$) in solution.

pH

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

Buffer

A substance or mixture containing a weak acid or weak base that resists changes in pH when an acid or base is added.

Salt

An ionic compound formed when the hydrogen ion of an acid is replaced by another cation.

Electrolytes

Substances (acids, bases, salts) whose dissociated ions in water conduct an electric current.

Non-electrolytes

Substances, such as sugars and alcohols, that do not form ions when dissolved in water and do not conduct electricity.