Chemistry Exam Review and Periodic Trends

Practice vocabulary flashcards based on the lecture covering previous exam topics (thermochemistry, stoichiometry, electron configurations) and periodic trends (atomic/ionic radii, ionization energies, electron affinity).

Hess's Law

A principle where known chemical equations and their corresponding $\Delta H$ values are manipulated (multiplied, flipped, or divided) and summed together to determine the overall enthalpy change of a target reaction.

Absorption (Electronic Transition)

An electronic transition where an electron moves from a lower energy level to a higher energy level by absorbing energy.

Emission (Electronic Transition)

An electronic transition where an electron drops from a higher energy level to a lower energy level, releasing energy in the process.

Hund's Rule

A rule of electron configuration stating that electrons occupy degenerate orbitals singly (separated) with parallel spins before they begin pairing up.

Standard Enthalpy of Formation ($\Delta H_f^\circ$) of an Element

The enthalpy of formation assigned a value of zero for any pure element existing in its most stable standard form.

Valence Electrons

Electrons residing in the outermost $s$ and $p$ subshells of main group elements that determine chemical reactivity and bonding capacity.

Effective Nuclear Charge

The net positive attraction that outermost electrons experience toward the protons in the nucleus, which increases across a period and decreases down a group.

Atomic Radius

The size of an atom, which decreases across a period due to increased positive charge pulling electrons closer, and increases down a group as additional electron shells ($n$) are added.

Cation Radius

The size of a positively charged ion, which is always smaller than its parent neutral atom because the same number of nuclear protons pulls a reduced number of electrons more tightly.

Anion Radius

The size of a negatively charged ion, which is always larger than its parent neutral atom because added electrons increase electron-electron repulsion without an increase in protons.

Isoelectronic

A term describing atoms or ions that possess the exact same total number of electrons, where species with more protons pull the electrons tighter and have a smaller radius.

First Ionization Energy

The quantity of energy required to remove the first outermost electron from a neutral atom to form a cation with a $+1$ charge.

Second Ionization Energy ($IE_2$)

The energy required to remove an electron from an existing $+1$ cation in order to produce a $+2$ cation.

Core Ionization Energy Jump

A large, disproportionate spike observed in successive ionization energies that occurs once all outer valence electrons have been removed and an electron must be pulled from an inner core shell.

Half-Filled / Fully Filled Subshell Stability

The enhanced thermodynamic stability associated with completely full or exactly half-full subshells, responsible for configuration exceptions (e.g., chromium and copper) and trend anomalies (such as nitrogen having a higher ionization energy than oxygen).

Electron Affinity

The energy change associated with adding an electron to a neutral atom to form an anion; a larger negative value indicates a stronger tendency or desire to gain an electron.