Ionic, Covalent, and Metallic Bonds: Properties and Formation

Posted on Nov 30, 2025 in Chemistry

Ionic Bonds: Formation and Properties

An ionic bond is a chemical link formed between a metal and a non-metal. This typically involves elements from groups such as:

  • Group IA: Alkali Metals
  • Group IIA: Alkaline Earth Metals
  • Group VIA: Chalcogens
  • Group VIIA: Halogens

Characteristics of Ionic Compounds

  • High Melting and Boiling Points: The ionic bond is very strong. A significant amount of energy is required to overcome the electrostatic forces of attraction between the ions in the crystal lattice.
  • Hard but Brittle Solids: In their solid state, ionic compounds are hard. However, they are also brittle. The ions are arranged in a fixed crystal lattice. A sharp blow can displace layers of ions, bringing ions with like charges close together. The resulting repulsive forces can cause the crystal to shatter.
  • Solubility: They are often soluble in polar solvents like water. The polar nature of these solvent molecules allows them to attract the anions and cations, pulling them apart from the lattice and dissolving the compound.
  • Electrical Conductivity: In the solid state, ionic compounds do not conduct electricity because their ions are held in fixed positions. However, they become good electrical conductors when molten or dissolved in water, as the ions are then free to move and carry an electric current.

Covalent Bonds: Sharing Electrons

A covalent bond is formed between non-metal atoms. These elements are typically electronegative and seek to gain electrons to achieve a stable electron configuration (an octet). Since neither atom will readily give up an electron, they achieve stability by sharing electrons.

Types of Covalent Bonds

Covalent bonds can be single, double, or triple, depending on the number of electron pairs shared:

  • Single Bond: One pair of electrons is shared between two atoms (e.g., H2, F2).
  • Double Bond: Two pairs of electrons are shared between two atoms (e.g., O2, CO2).
  • Triple Bond: Three pairs of electrons are shared between two atoms (e.g., N2, HCN).

In some cases, one atom provides both electrons to form the shared pair. This is known as a coordinate covalent bond, as seen in the hydronium ion (H3O+).

Polarity of Covalent Bonds

The sharing of electrons can be equal or unequal, leading to two types of covalent bonds:

  • Nonpolar Covalent Bond: Formed between identical atoms (or atoms with very similar electronegativity). The electron distribution is symmetrical.
  • Polar Covalent Bond: Formed between atoms with different electronegativities. The electron distribution is asymmetrical, as the more electronegative atom attracts the shared electrons more strongly, creating partial positive and negative charges.

Weak intermolecular forces of attraction exist between covalent molecules. While weak, these forces are crucial as they determine the physical properties, such as the state of matter (solid, liquid, or gas), of covalent substances.

Metallic Bonds: The Electron Sea Model

A metallic bond is the force of attraction between valence electrons and the metal ions. It is the sharing of a sea of delocalized electrons among a lattice of positive ions (cations).

Metals are electropositive elements whose atoms have few valence electrons and tend to lose them easily. In a metallic solid, these electrons are not transferred to another atom but are delocalized across the entire structure.

The Electron Cloud Model

  • Metal atoms release their valence electrons, becoming positive cations arranged in a fixed lattice structure.
  • The released valence electrons form a delocalized “sea” or “cloud” of electrons that moves freely throughout the lattice. This electron sea holds the cations together, balancing the repulsive forces between them.

Properties of Metals

  • High Melting and Boiling Points: Most metals have high melting and boiling points because the metallic bond is strong and stable, creating a giant, robust structure.
  • Insolubility: They are generally insoluble in water because the strong metallic bonds cannot be easily overcome by water molecules.
  • Malleable and Ductile: Metals are malleable (can be hammered into sheets) and ductile (can be drawn into wires). The layers of cations can slide over one another without breaking the metallic bond, as the electron sea adjusts to the new shape.
  • Luster: They have a characteristic shine or luster. The free electrons in the electron sea can absorb and immediately re-emit photons of light.
  • Electrical Conductivity: They are excellent conductors of electricity. The delocalized electrons are free to move throughout the structure and can carry an electric current when a voltage is applied.
  • Thermal Conductivity: They are also good conductors of heat. The mobile valence electrons can efficiently transfer kinetic energy (heat) from one part of the metal to another.