Chemistry: Atomic Structure, Electrons, Periodic Table, and States of Matter

Comprehensive vocabulary flashcards covering key definitions from the chapters on atomic structure, electron models and configurations, periodic table organization and trends, and the kinetic theory and states of matter.

Atom

The smallest particle of an element that retains its identity in a chemical reaction.

Dalton's atomic theory

The first theory to relate chemical changes to events at the atomic level, stating that all elements are composed of indivisible atoms, atoms of the same element are identical, atoms of different elements combine in whole-number ratios, and chemical reactions rearrange atoms without changing them into atoms of another element.

Electrons

Negatively charged subatomic particles discovered by J. J. Thomson in 1897.

Cathode ray

A glowing beam of electrons that travels from the cathode to the anode in a cathode-ray tube.

Protons

Positively charged subatomic particles that have a mass about $1840$ times that of an electron.

Neutrons

Subatomic particles with no electrical charge and a mass nearly equal to that of a proton.

Nucleus

The tiny, dense central core of an atom that is composed of protons and neutrons.

Atomic number

The number of protons in the nucleus of an atom of a specific element.

Energy levels

The fixed energies that an electron can possess in an atom.

Quantum

The amount of energy required to move an electron from one energy level to another energy level.

Quantum mechanical model

The modern mathematical description of the behavior of electrons in atoms, which determines the allowed energies an electron can have and the probability of finding it in various locations around the nucleus.

Atomic orbital

A mathematical expression describing the probability of finding an electron at various locations around the nucleus, often thought of as a region of space where there is a high probability of finding an electron.

Electron configurations

The ways in which electrons are arranged in various orbitals around the nuclei of atoms.

Aufbau principle

The rule that electrons occupy the orbitals of lowest energy first.

Pauli exclusion principle

The rule stating that an atomic orbital may describe at most two electrons, and each must have an opposite spin.

Hund's rule

The rule stating that electrons occupy orbitals of equal energy in a way that makes the number of electrons with the same spin direction as large as possible.

Amplitude

The height of a wave from zero to the crest.

Wavelength

The distance between crests of a wave, represented by the Greek letter lambda ($\lambda$).

Frequency

The number of wave cycles to pass a given point per unit of time, represented by the Greek letter nu ($\nu$).

Hertz (Hz)

The SI unit of wave frequency equal to one cycle per second or a reciprocal second ($\text{s}^{-1}$).

Electromagnetic radiation

Energy waves that travel in a vacuum at a speed of $2.998 \times 10^8\,\text{m/s}$, including radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays.

Spectrum

The colored band produced when sunlight or white light passes through a prism, separating into its component frequencies.

Atomic emission spectrum

The pattern of discrete lines of specific frequencies emitted by an element when its electrons lose energy returning to lower energy levels.

Ground state

The lowest possible energy state of an atom, where the principal quantum number ($n$) is equal to $1$.

Photons

Quanta of light energy that behave as if they were particles.

Heisenberg uncertainty principle

The principle stating that it is impossible to know exactly both the velocity and the position of a particle at the same time.

Periodic table

An arrangement of elements into groups based on a set of repeating properties.

Periodic law

The principle that when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

Metals

Elements that are generally good conductors of heat and electric current, exhibit high luster, and are typically malleable and ductile solids at room temperature (with the exception of mercury).

Nonmetals

Elements that are generally poor conductors of heat and electric current, show greater variation in physical properties, and tend to be brittle when solid.

Metalloid

An element that generally has properties similar to those of both metals and nonmetals depending on prevailing conditions.

Alkali metals

The metallic elements located in Group 1A of the periodic table.

Alkaline earth metals

The metallic elements located in Group 2A of the periodic table.

Halogens

The nonmetallic elements located in Group 7A of the periodic table.

Noble gases

The nonmetallic elements in Group 8A of the periodic table, which have completely filled $s$ and $p$ sublevels in their highest occupied energy levels.

Representative elements

Elements in Groups 1A through 7A whose highest occupied $s$ and $p$ sublevels are not completely filled.

Transition metal

Group B elements displayed in the main body of the periodic table, characterized by the presence of electrons in $d$ orbitals.

Inner transition metal

Elements appearing below the main body of the periodic table, characterized by the presence of electrons in $f$ orbitals.

Atomic radius

One half of the distance between the nuclei of two atoms of the same element when the atoms are joined.

Ion

An atom or group of atoms that has acquired a positive or negative charge through the loss or gain of electrons.

Cation

An ion with a positive electrical charge, formed when an atom loses one or more electrons.

Anion

An ion with a negative electrical charge, formed when an atom gains one or more electrons.

Ionization energy

The energy required to remove an electron from an atom in its gaseous state.

Electronegativity

The ability of an atom of an element to attract electrons when the atom is in a compound.

Kinetic energy

The energy an object possesses because of its motion.

Kinetic theory

A fundamental theory stating that all matter consists of tiny particles that are in constant motion.

Gas pressure

The force exerted by a gas per unit surface area of an object, resulting from simultaneous collisions of billions of rapidly moving particles with that object.

Vacuum

An empty space containing no particles and having no pressure.

Atmospheric pressure

The pressure resulting from the collisions of atoms and molecules in air with objects.

Barometer

A device used to measure atmospheric pressure.

Pascal (Pa)

The SI unit of pressure.

Standard atmosphere (atm)

A unit of pressure defined as the pressure required to support $760\,\text{mm}$ of mercury in a mercury barometer at $25^\circ\text{C}$, equal to $101.3\,\text{kPa}$.

Vaporization

The conversion of a liquid into a gas or vapor.

Evaporation

The vaporization of a liquid that occurs specifically at the surface of a liquid that is not boiling.

Vapor pressure

A measure of the force exerted by a gas above a liquid in a closed container.

Boiling point

The temperature at which the vapor pressure of a liquid equals the external pressure on the liquid.

Normal boiling point

The boiling point of a liquid measured at a standard external pressure of $101.3\,\text{kPa}$.

Melting point

The temperature at which a solid changes into a liquid, where the disruptive vibrations of particles overcome attractive forces holding them in place.

Crystal

A solid substance in which the constituent particles are arranged in an orderly, repeating, three-dimensional pattern known as a crystal lattice.

Unit cell

The smallest group of particles within a crystal that retains the complete geometric shape of the crystal.

Allotropes

Two or more different molecular forms of the same element in the same physical state.

Amorphous solid

A solid that lacks an ordered internal structure, having randomly arranged atoms or molecules.

Glass

A transparent fusion product of inorganic substances that have cooled to a rigid state without crystallizing, often called a supercooled liquid.

Sublimation

The change of a substance directly from a solid to a vapor without passing through the liquid state.