Ionic Bonds and Electronic Configurations of Ions (CHEM101 Chapter 6 Study Notes)

Ionic Bonds and Electronic Configurations of Ions

Introduction to Ionic Bonds

Ionic bonds are a fundamental type of chemical bond formed through the transfer of electrons from one atom to another, resulting in the creation of ions. This process typically occurs between metals and nonmetals, leading to strong electrostatic attractions between oppositely charged particles.

• Ionic Bond: A chemical bond resulting from the transfer of one or more electrons from a metal to a nonmetal, producing ions with opposite charges.

• Cation: A positively charged ion, usually formed when a metal loses electrons.

• Anion: A negatively charged ion, usually formed when a nonmetal gains electrons.

• Example: Sodium (Na) loses one electron to form Na+, while chlorine (Cl) gains one electron to form Cl-. These ions attract each other to form NaCl.

Electron Configurations of Ions

When atoms form ions, their electron configurations change to reflect the loss or gain of electrons. Most main-group ions achieve noble gas configurations, which are particularly stable.

• Loss of Electrons (Cations): Metals lose electrons from their highest energy level (valence shell) to form cations.

• Gain of Electrons (Anions): Nonmetals gain electrons to fill their valence shell, forming anions.

• Example:

  • Na: $1s^2\ 2s^2\ 2p^6\ 3s^1$ → Na+: $1s^2\ 2s^2\ 2p^6$ (same as Ne)

  • Mg: $1s^2\ 2s^2\ 2p^6\ 3s^2$ → Mg2+: $1s^2\ 2s^2\ 2p^6$

  • Al: $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^1$ → Al3+: $1s^2\ 2s^2\ 2p^6$

  • N: $1s^2\ 2s^2\ 2p^3$ → N3-: $1s^2\ 2s^2\ 2p^6$

  • O: $1s^2\ 2s^2\ 2p^4$ → O2-: $1s^2\ 2s^2\ 2p^6$

  • F: $1s^2\ 2s^2\ 2p^5$ → F-: $1s^2\ 2s^2\ 2p^6$

Table: Common Main-Group Ions and Their Noble Gas Electron Configurations

This table summarizes the electron configurations of selected main-group ions, showing how they achieve noble gas configurations.

Group 2A	Group 3A	Group 6A	Group 7A	Electron Configuration
Be2+	Al3+	O2-	F-	[He]
Mg2+	Ga3+	S2-	Cl-	[Ne]
Ca2+	In3+	Se2-	Br-	[Ar]
Sr2+	Tl3+	Te2-	I-	[Kr]
Ba2+				[Xe]

Additional info: Some ions do not have a true noble gas configuration because they have an incomplete subshell.

Transition Metal Ions: Electron Configurations

Transition metals lose electrons first from their outermost s orbital, then from the d orbitals. Their ions often do not achieve noble gas configurations.

• Example:

  • Fe: [Ar] 4s2 3d6

  • Fe2+: [Ar] 3d6 (loss of 2 electrons)

  • Fe3+: [Ar] 3d5 (loss of 3 electrons)

• Atomic Size Trend: The size of the ion decreases as more electrons are removed due to reduced electron-electron repulsion.

Trends in Ionic Radii

The size of ions compared to their parent atoms depends on whether the ion is a cation or anion.

• Cations: Smaller than their neutral atoms because they lose electrons, reducing electron-electron repulsion and often losing an entire valence shell.

• Anions: Larger than their neutral atoms because they gain electrons, increasing electron-electron repulsion and expanding the electron cloud.

• Example: Na+ is smaller than Na; Cl- is larger than Cl.

Table: Comparison of Ionic and Atomic Radii

Element	Atomic Radius	Ionic Radius	Trend
Na	Neutral	Na+ (smaller)	Cation < smaller
Cl	Neutral	Cl- (larger)	Anion > larger
Mg	Neutral	Mg2+ (smaller)	Cation < smaller
F	Neutral	F- (larger)	Anion > larger

Summary of Key Points

• Ionic bonds form through electron transfer, creating cations and anions.

• Main-group ions often achieve noble gas electron configurations.

• Transition metal ions lose s electrons first, then d electrons; they may not reach noble gas configurations.

• Cations are smaller than their parent atoms; anions are larger.

• Electron configuration changes are crucial for understanding chemical reactivity and properties of ionic compounds.