Chemical Bonds: Ionic, Covalent, and Metallic

Posted on Mar 10, 2025 in Chemistry

Understanding Chemical Bonds: Types and Properties

A chemical bond arises when atoms interact, leading to compounds with lower energy than the separated atoms. To achieve a noble gas configuration, atoms can gain, lose, or share electrons. Depending on how this is achieved, bonds can be ionic, covalent, or metallic. The properties of compounds depend on the type of bond between their atoms.

Ionic Bond

An ionic bond occurs between metallic and nonmetallic elements. Metals give up their extra electrons to acquire a noble gas configuration, and nonmetals gain electrons to achieve the same. This transfer of electrons happens when metals and nonmetals are in proximity.

  1. Perform the electron configuration.
  2. Determine the extra electrons in the metal and the missing electrons in the nonmetal.
  3. Draw an arrow indicating the electron transfer from the metal to the nonmetal.

Properties of Ionic Compounds:

  • They are crystalline solids.
  • They have high melting and boiling points.
  • They are soluble in polar solvents (e.g., H2O).
  • In the solid state, they do not conduct electrical current (but they can when molten or dissolved).
  • They are hard but brittle.

Covalent Bond

A covalent bond arises when combining nonmetallic elements, which can be the same or different. In this case, all atoms need to gain electrons to stabilize. To achieve a noble gas configuration, electrons are shared. Covalent compounds generally do not conduct electricity.

  1. Place the atoms, typically two on the sides and one in the center.
  2. Place the electrons around each atom.
  3. Connect the atoms until everyone has 8 electrons (Hydrogen only needs 2).

Geometry of Molecules:

Lone pairs: Number of electrons of the central atom that are not shared.

Number of directions: Number of elements with which the central atom shares electrons (for each lone pair, add one more direction).

  • 2 directions: Linear, 180°
  • 3 directions: Trigonal planar, 120°
  • 4 directions: Tetrahedral, 109°
  • 5 directions: Bipyramidal, 120°, 90°

Polar: Has lone pairs.

Nonpolar: Has no lone pairs.

Properties of Covalent Compounds

There are two types of covalent compounds:

Covalent Molecular Substances:
  1. They are usually gases, liquids, or solids with low melting points.
  2. They have low melting and boiling points.
  3. Polar molecules are soluble in polar solvents, and nonpolar molecules dissolve in nonpolar solvents.
  4. They do not conduct electricity.
Atomic Covalent Crystals:
  1. They are solid, crystalline, very compact structures where the nodes of the crystal are occupied by atoms. They are very hard but brittle.
  2. They do not dissolve in any solvent.
  3. They do not conduct electricity (with some exceptions, like graphite).
  4. They have high melting points because the covalent bond between the atoms in the crystal is very strong. (Example: Quartz)

Intermolecular Forces (Van Der Waals Forces)

These are the forces established between molecules of a covalent compound. These forces are much weaker than the bonds themselves. They unite the various molecules, and their intensity depends mainly on the electronegativity difference between the atoms forming the molecule and the size of the atoms. The greater these factors, the more intense the force between molecules.

Intermolecular forces are due to electrostatic attraction between permanent dipoles in heteronuclear molecules or induced dipoles in homonuclear molecules. The more intense the intermolecular forces, the greater the state of aggregation and the higher the melting and boiling points.

In homonuclear molecules, instantaneous deflection of the electron cloud is easier the larger the size of the atoms. In this sense, deformability increases, thus explaining the different aggregation states of halogens.