Atomic Structure, Periodic Trends, and Ionic Compounds: Study Notes

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Atomic Structure and Electron Configuration

Electron Configuration Principles

Understanding electron configuration is fundamental to predicting chemical behavior and properties of elements. Electron configuration describes the arrangement of electrons in an atom's orbitals.

Key Point 1: Electron configurations are determined by the Aufbau principle, Pauli exclusion principle, and Hund's rule.
Key Point 2: For transition metals, more than one stable electron configuration may exist due to the involvement of d-orbitals.
Example: The electron configuration of Fe (Iron) is [Ar] 4s2 3d6, but in its common ion Fe2+, it is [Ar] 3d6.

Periodic Trends: Ionic Radii and Ionization Energy

Ionic Radii Trends

Ionic radii refer to the size of ions in the periodic table, which varies based on electron configuration and nuclear charge.

Key Point 1: Cations are generally smaller than their parent atoms due to loss of electrons and increased effective nuclear charge.
Key Point 2: Anions are larger than their parent atoms due to electron gain and decreased effective nuclear charge.
Example: Na+ is smaller than Na, while Cl- is larger than Cl.

Ionization Energy

Ionization energy is the energy required to remove an electron from a gaseous atom or ion.

Key Point 1: Ionization energy increases across a period and decreases down a group.
Key Point 2: Large jumps in ionization energy indicate removal of electrons from a new, lower energy shell.
Formula:
Example: The first ionization energy of Na is much lower than the second, as the second electron is removed from a closed shell.

Electron Affinity and the Octet Rule

Electron Affinity

Electron affinity is the energy change when an atom gains an electron to form an anion.

Key Point 1: Electron affinity is generally more negative across a period, indicating a greater tendency to gain electrons.
Key Point 2: Formation of anions is favored when electron affinity is highly negative.
Example: Chlorine has a high (negative) electron affinity, making it likely to form Cl-.

The Octet Rule

The Octet Rule states that atoms tend to gain, lose, or share electrons to achieve a full set of eight valence electrons.

Key Point 1: The Octet Rule explains the stability of noble gases and the reactivity of other elements.
Key Point 2: Exceptions include elements with incomplete or expanded octets (e.g., H, B, P, S).
Example: Oxygen forms O2- to achieve a noble gas configuration.

Ionic Bonding and Energy Changes

Bond Formation and Energy

Energy changes occur during ionic bond formation, including ionization energy, electron affinity, and lattice energy.

Key Point 1: Ionic bonds form when electrons are transferred from a metal to a nonmetal, resulting in oppositely charged ions.
Key Point 2: The energy released during bond formation stabilizes the ionic compound.
Example: NaCl forms from Na and Cl through electron transfer and subsequent attraction.

Born-Haber Cycle

The Born-Haber cycle is a thermodynamic cycle used to analyze the energy changes in the formation of ionic compounds.

Key Point 1: The cycle includes steps such as sublimation, ionization, dissociation, electron affinity, and lattice energy.
Key Point 2: The overall enthalpy change for formation can be calculated by summing the individual steps.
Formula:
Example: The formation of NaCl from Na(s) and Cl2(g) can be analyzed using the Born-Haber cycle.

Lattice Energy and Coulomb's Law

Lattice Energy

Lattice energy is the energy released when gaseous ions combine to form an ionic solid.

Key Point 1: Lattice energy is a measure of the strength of the ionic bonds in a crystal lattice.
Key Point 2: It can be estimated using Coulomb's Law, which relates the energy to the charges and distance between ions.
Formula:
Example: MgO has a higher lattice energy than NaCl due to higher ionic charges and smaller ionic radii.

Comparison Table: Periodic Trends and Properties

The following table summarizes key periodic trends and their effects on atomic and ionic properties.

Property	Trend Across Period	Trend Down Group	Effect on Ions
Ionization Energy	Increases	Decreases	Higher for cations, lower for anions
Electron Affinity	More negative	Less negative	Favors anion formation
Ionic Radius	Decreases for cations, increases for anions	Increases	Cations smaller, anions larger than parent atom
Lattice Energy	Increases with charge	Decreases with size	Stronger for small, highly charged ions