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 become Na+, while chlorine (Cl) gains one electron to become Cl-. The resulting NaCl is held together by ionic bonds.

Formation of Ions and Their Electron Configurations

Atoms form ions by gaining or losing electrons to achieve a stable electron configuration, often resembling that of the nearest noble gas. The electron configuration of ions can be predicted based on the number of electrons lost or gained.

• Metal Atoms: Lose electrons to form cations with noble gas configurations.

• Nonmetal Atoms: Gain electrons to form anions with noble gas configurations.

Atom	Electron Configuration	Ion	Electron Configuration
Na	1s2 2s2 2p6 3s1	Na+	1s2 2s2 2p6
Mg	1s2 2s2 2p6 3s2	Mg2+	1s2 2s2 2p6
Al	1s2 2s2 2p6 3s2 3p1	Al3+	1s2 2s2 2p6
N	1s2 2s2 2p3	N3-	1s2 2s2 2p6
O	1s2 2s2 2p4	O2-	1s2 2s2 2p6
F	1s2 2s2 2p5	F-	1s2 2s2 2p6

Note: The resulting electron configuration for these ions matches that of neon (Ne), a noble gas.

Common Main-Group Ions and Their Noble Gas Electron Configurations

Main-group elements tend to form ions that have the same electron configuration as the nearest noble gas. The following table summarizes common ions and their configurations:

Group 1A	Group 2A	Group 3A	Group 6A	Group 7A	Electron Configuration
Na+	Be2+	Al3+	O2-	F-	[He]
K+	Mg2+	Ga3+	S2-	Cl-	[Ne]
Rb+	Ca2+	In3+	Se2-	Br-	[Ar]
Cs+	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 and Electron Configurations

Transition metals form cations by losing electrons first from the highest principal quantum number (usually the s orbital) before the d orbitals. Their electron configurations change accordingly.

• Example: Iron (Fe) has the electron configuration [Ar] 4s2 3d6. When forming Fe2+, it loses two electrons: [Ar] 3d6. For Fe3+, it loses three electrons: [Ar] 3d5.

• Atomic Size Trend: As more electrons are removed (Fe → Fe2+ → Fe3+), electron-electron repulsion decreases and the atomic size of the ion decreases.

Trends in Ionic Radii

The size of ions compared to their neutral atoms varies depending on whether the ion is a cation or anion.

• Cations: Are smaller than their neutral atoms due to the loss of electrons and a decrease in electron-electron repulsion. The principal quantum number of the valence shell is also lower.

• Anions: Are larger than their neutral atoms because the addition of electrons increases electron-electron repulsion and expands the electron cloud.

Cation	Neutral Atom Size	Cation Size
Na+	larger	smaller
K+	larger	smaller
Mg2+	larger	smaller
Ca2+	larger	smaller

Anion	Neutral Atom Size	Anion Size
F-	smaller	larger
Cl-	smaller	larger
Br-	smaller	larger
I-	smaller	larger

Summary Table: Key Properties of Ions

Type	Formation	Size Change	Example
Cation	Loss of electrons	Smaller than atom	Na → Na+
Anion	Gain of electrons	Larger than atom	Cl → Cl-

Additional info:

• Effective nuclear charge (Zeff) increases for cations, leading to a smaller ionic radius.

• Electron-electron repulsion increases for anions, leading to a larger ionic radius.