Chapter 3: Atoms and Atomic Theory

A set of 50 comprehensive vocabulary flashcards covering atomic structure, classical and quantum developments, quantum numbers, electron configurations, and applications from Chapter 3.

Electron

A negatively charged subatomic particle.

Radioactivity

The spontaneous decay or disintegration of the nucleus of an atom.

Nucleus

The dense centre of an atom with a positive charge.

Proton

A positively charged subatomic particle found in the atomic nucleus.

Neutron

An electrically neutral subatomic particle found in the atomic nucleus.

Isotopes

Atoms with the same number of protons but different numbers of neutrons.

Atomic number ($Z$)

The number of protons in a nucleus.

Mass number ($A$)

The total number of protons and neutrons in a nucleus.

Radioisotope

An isotope with an unstable nucleus that decays and emits radioactive gamma rays and/or subatomic particles (for example, alpha and/or beta particles).

Photoelectric effect

The phenomenon in which electrons are emitted by matter that absorbs energy from shortwave electromagnetic radiation (such as visible or UV light).

Quantum

A discrete unit or packet of energy (plural: quanta).

Photon

A unit of light energy.

Planck's constant ($h$)

A constant of nature with the value $6.63 \times 10^{-34}\,\text{J}\cdot\text{s}$, relating the energy of radiation to its frequency in the equation $E = nhf$.

Threshold frequency

The minimum frequency of light required to eject electrons from a metal surface in the photoelectric effect.

Spectroscopy

The analysis of spectra to determine properties of their source.

Emission spectrum

The spectrum of electromagnetic radiation emitted by an atom; results when an atom returns to a lower energy state from a higher energy state.

Continuous spectrum

An emission spectrum that contains all the wavelengths in a specific region of the electromagnetic spectrum.

Line spectrum

An emission spectrum that contains only those wavelengths characteristic of the element being studied.

Transition

The movement of an electron from one energy level to another.

Ground state

The lowest possible energy state for an atom.

Quantum mechanics

The application of quantum theory to explain the properties of matter, particularly electrons in atoms.

Node

A point of zero lateral displacement in a standing wave, or an area of zero probability of finding an electron in an orbital.

Antinode

The point in a standing wave between two nodes where the amplitude of the wave is at its maximum.

Orbital

The region around the nucleus where an electron has a high probability of being found.

Heisenberg’s uncertainty principle

The principle stating that it is impossible to simultaneously know the exact position and speed of an electron at a given time.

Wave function

The mathematical probability of finding an electron in a certain region of space.

Electron probability density

The probability of finding an electron at a given location, derived from wave equations and used to determine the shapes of orbitals; also called electron probability distribution.

Quantum mechanical model

A model for the atom based on quantum theory and the calculation of probabilities for the location of electrons.

Quantum numbers

Numbers that describe the quantum mechanical properties of orbitals; derived from the solutions to Schrödinger's wave equation.

Shell

An atom’s main energy level, where the shell number is given by the principal quantum number, $n = 1, 2, 3, \dots$.

Principal quantum number ($n$)

The quantum number that describes the size and energy of an atomic orbital, having whole-number values $1, 2, 3, \dots$.

Subshells

Orbitals of different shapes and energies within a shell, as given by the secondary quantum number; often referred to as $s$, $p$, $d$, and $f$.

Secondary quantum number ($l$)

The quantum number that describes the shape and energy of an atomic orbital, with whole-number values from $0$ to $n - 1$ for each value of $n$.

Magnetic quantum number ($m_l$)

The quantum number that describes the orientation of an atomic orbital in space relative to the other orbitals in the atom, with whole-number values between $+l$ and $-l$, including $0$.

Spin quantum number ($m_s$)

The quantum number that relates to the spin of the electron; limited to values of $+\frac{1}{2}$ or $-\frac{1}{2}$.

Pauli exclusion principle

The principle stating that in a given atom, no two electrons can have the same set of four quantum numbers ($n, l, m_l, m_s$).

Electron configuration

The location and number of electrons in the electron energy levels of an atom.

Aufbau principle

The theory that an atom is 'built up' by the addition of electrons, which fill orbitals starting at the lowest available energy orbital before filling higher energy orbitals.

Energy-level diagram (orbital diagram)

A diagram that represents the relative energies of the electrons in an atom.

Hund’s rule

A rule stating that in a particular set of orbitals of the same energy, the lowest energy configuration for an atom is the one with the maximum number of unpaired electrons allowed by the Pauli exclusion principle; unpaired electrons are represented as having parallel spins.

Valence electron

An electron in the outermost principal quantum level of an atom.

Transition metal

An element whose highest-energy electrons are in $d$ orbitals.

Representative elements

Those elements in the main blocks of the periodic table, which are Groups 1 to 18 (the $s$ and $p$ blocks).

Ferromagnetism

The very strong magnetism commonly exhibited by materials that contain nickel, iron, and cobalt; applies to a collection of atoms organized into magnetic domains.

Paramagnetism

The weak attraction of a substance to a magnet caused by the presence of unpaired electrons; applies to individual atoms.

Laser

An acronym for light amplification by stimulated emission of radiation; a device that produces light of a single colour with all waves travelling parallel to each other.

Bose–Einstein condensate (BEC)

A state of matter that consists of a collection of atoms near absolute zero ($0\,\text{K}$ or $-273.15\,^\circ\text{C}$), where all the atoms have the lowest possible quantum energy state.

Magnetic resonance imaging (MRI)

A medical diagnostic tool in which magnetic fields and radio frequencies interact with atoms (particularly hydrogen) in the human body to produce detailed images of soft tissues.

Scanning tunnelling microscope (STM)

A special microscope that passes an extremely fine, electrically charged needle over the surface of an object to image individual atoms based on current variations.

Nanotechnology

The science of working with structures that are between $1\,\text{nm}$ and $100\,\text{nm}$ long in at least one dimension.

exceptions to octet rule

-H (max 2e-)

-Be (only 4 e-)

-B (only 6 e-)

-P, S, Cl, I, Xe (can have expanded octets)