Atomic Structure and Electron Configurations

Vocabulary practice flashcards covering atomic structure, isotopes, main energy levels, sublevels, orbitals, electron spin, quantum mechanical principles (Aufbau, Pauli exclusion, Hund's rule), and notation methods.

Atomic Number ($Z$)

The number of protons in each atom of an element, which uniquely identifies the element and equals the number of electrons in an electrically neutral atom.

Mass Number ($A$)

The total number of protons and neutrons that make up the nucleus of an atom or isotope ($\text{protons} + \text{neutrons}$).

Isotopes

Atoms of the same element that have the same number of protons and electrons (same atomic number) but different numbers of neutrons and therefore different masses.

Protium

The most common isotope of hydrogen, accounting for $99.9885\%$ of hydrogen atoms on Earth; its nucleus consists of one proton and zero neutrons, giving it a mass number of 1.

Deuterium

An isotope of hydrogen whose nucleus contains two particles: one proton and one neutron, giving it a mass number of 2.

Tritium

A hydrogen isotope having a nucleus of one proton and two neutrons, giving it a mass number of 3.

Tin

The metallic element that possesses 10 stable isotopes, which is more than any other element.

Compound

A substance formed from different types of atoms chemically bonded together, such as water ($H_2O$), which is composed of two hydrogen atoms and one oxygen atom.

Main Energy Level ($n$)

The principal energy level of an electron shell (designated by integers $n = 1, 2, 3, 4\dots$ or letters $K, L, M, N, O, P, Q$), which has a maximum capacity of $2n^2$ electrons.

Sublevel

A subdivision of a principal energy level designated by $s$, $p$, $d$, or $f$, which contain 1, 3, 5, and 7 orbitals respectively.

Orbital

A region within a sublevel that can hold a maximum of 2 electrons with opposite spins.

Aufbau Principle

The principle stating that an electron occupies the lowest-energy orbital that can receive it (for instance, filling the $4s$ sublevel before the $3d$ sublevel).

Pauli Exclusion Principle

The principle stating that no two electrons in the same atom can have the same set of four quantum numbers; an individual orbital can hold at most two electrons, and they must have opposite spins.

Hund's Rule

The rule stating that orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all single electrons in these orbitals must have parallel (the same) spins.

Electron Configuration

The specific arrangement of electrons among the orbitals and sublevels of an atom, unique to each chemical element.

Ground-State Electron Configuration

The arrangement of electrons in an atom in which the total energy is at its lowest possible value.

Orbital Notation

A representation of electron configuration where each orbital is shown as a horizontal line or box labeled with its sublevel name below, and electrons are drawn as upward or downward arrows above the line.

Electron-Configuration Notation

A shorthand notation that eliminates lines and arrows, displaying the number of electrons in each sublevel as a superscript number to the top right of the sublevel designation (e.g., $1s^2 2s^2 2p^6 3s^2 3p^4$ for sulfur).

Noble-Gas Notation

A method of writing electron configurations that uses the bracketed chemical symbol of a noble gas to substitute for the full configuration of inner-shell electrons.

Valence Electrons

The electrons situated in the outermost energy level (outermost layer) of an atom, which can be represented visually as dots in electron-dot notation.

Electron Spin

The quantum state specifying the orientation of an electron's angular momentum within an orbital, represented as either a $+\frac{1}{2}$ spin state (up arrow, $\uparrow$) or a $-\frac{1}{2}$ spin state (down arrow, $\downarrow$).

Quantum Model of the Atom

The atomic model that improves upon Bohr's model by deriving energy states mathematically from Schrödinger's equation and describing electron arrangements in atoms beyond hydrogen.