Chemistry for Pharmacy - Orbitals and Bonding Vocabulary

Vocabulary practice flashcards covering foundational chemistry topics for pharmacy students, including atomic structure, orbital filling rules, chemical bonding, valence bond theory, and molecular orbital theory.

Nucleus

A very small region ($10^{-14}$ to $10^{-15}\,\text{m}$) at the center of an atom containing protons and neutrons, holding essentially all of the atom's mass.

Atomic Number

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

Mass Number

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

Atomic Orbital

A region of space around a nucleus that describes the probability of locating an electron, characterized by a specific shape and energy.

Node

A planar or spatial region of zero electron density separating the lobes of an atomic orbital, such as in a p orbital.

Degenerate Orbitals

Atomic orbitals that belong to the same subshell and possess equal energy levels, such as the three 2p orbitals.

Ground State

The lowest-energy, most stable electronic arrangement of electrons in an atom's orbitals.

Core Electrons

Electrons residing in completely filled inner shell orbitals that generally do not participate in chemical reactions.

Valence Electrons

Electrons located in incomplete outer shell orbitals that are available to form bonds and engage in chemical reactions.

Aufbau Principle

The rule stating that atomic orbitals are filled in order of increasing energy, starting from the lowest available level ($1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d$).

Pauli Exclusion Principle

The rule establishing that an atomic orbital can hold a maximum of two electrons, provided they have opposite spins.

Hund's Rule

The rule dictating that orbitals of equal energy must each be occupied by a single electron before any orbital is doubly occupied with opposite spins.

Octet Rule

The principle that main-group elements are most stable when their valence shell contains $8$ electrons (or is completely filled), leading them to transfer or share electrons.

Valency

The combining capacity of an element, determined by the number of electrons an atom loses, gains, or shares to achieve a stable outer shell.

Ionic Bonding

The electrostatic attraction holding oppositely charged ions together, formed when electropositive elements transfer electrons to electronegative elements.

Covalent Bond

A chemical linkage formed between two non-metal atoms through the mutual sharing of one or more electron pairs.

Lewis Structure

A structural depiction of a molecule that explicitly shows all valence electrons as dots, including bonding pairs and unshared non-bonding pairs.

Kekulé Structure

A structural formula where covalent bonds are drawn as solid lines connecting atoms, while lone-pair valence electrons are omitted.

Valence Bond Theory

A quantum mechanical model describing a covalent bond as the head-on or side-by-side overlap of singly occupied atomic orbitals from two approaching atoms.

Sigma ($\sigma$) Bond

A covalent bond formed by the direct head-on overlap of atomic orbitals, possessing cylindrical symmetry along the internuclear axis.

Bond Strength

The quantity of energy released when a chemical bond forms, or required to break that bond (e.g., $436\,\text{kJ\,mol}^{-1}$ for the $\text{H}-\text{H}$ bond).

Bond Length

The optimum internuclear distance between two bonded atoms at which potential energy is minimized (e.g., $0.74\,\text{\AA}$ or $74\,\text{pm}$ for $\text{H}_2$).

Molecular Orbital Theory

A theory postulating that atomic orbitals combine linearly (additively or subtractively) to form molecular orbitals distributed over the entire molecule.

Bonding Molecular Orbital

A low-energy, stabilizing molecular orbital produced by the additive combination of atomic wave functions, concentrating electron density between nuclei.

Antibonding Molecular Orbital

A high-energy, destabilizing molecular orbital containing a node between nuclei, formed by the subtractive combination of atomic wave functions.