Understanding Chemical Bonds: Types and Properties

Posted on Jan 30, 2025 in Chemistry

Chemical Bonds: Types and Properties

In chemical bonds, atoms tend to bind to each other to form more complex entities, which make up substances.

Ionic Bonds

When an atom that is missing a few electrons in its valence shell is faced with another atom of low electronegativity, an electron transfer occurs. This is common between metals and nonmetals. The fundamental process of electron transfer results in what is known as an ionic network or crystal. In ionic compounds, we cannot speak of individual molecules but rather of large aggregates. The formula does not represent a molecule but only indicates the proportion in which the ions are combined.

Properties of Ionic Compounds:

  • They are solid and crystalline, with a well-defined and orderly structure.
  • They have high melting and boiling points, requiring a lot of energy to break the bonds.
  • They are hard to scratch, as a solid link must be broken.
  • They are usually water-soluble, and when dissolved, they break into positive and negative ions.
  • In a solid state, they do not conduct electricity because the ions are tightly bound.
  • When fused or in an aqueous solution, they are good conductors of electric current due to the existence of mobile ions.
  • The greater the attraction between ions (higher charge and smaller distance between charges), the stronger the bond.

Covalent Bonds

The fundamental process of a covalent bond is electron sharing. The aim is to share electrons, thus acquiring a noble gas configuration. It is a link between atoms of high electronegativity (nonmetals). Molecules are the basic units of covalent compounds. Lewis diagrams are used to represent molecules, where valence electrons are represented by dots or crosses.

Coordinate Covalent Bond (Dative Bond):

It is possible that the shared electron pair is not composed of one electron from each of the bonded atoms, but both electrons are contributed by one of the atoms. This is called a coordinate covalent bond or dative bond and is represented by an arrow pointing from the atom that provides the electron pair to the receiver atom.

Properties of Covalent Compounds:

  • They are made of molecules.
  • They are usually gases or liquids.
  • They have lower melting and boiling points.
  • They are often poorly soluble in water.
  • They are poor conductors of electric current.

Metallic Bonds

Metallic bonding occurs with metals. It involves a very orderly and compact arrangement of positive metal ions (a lattice) distributed among the electrons lost by each atom in the form of an electron cloud.

Properties of Metallic Compounds:

  • They are solid at room temperature (except for mercury).
  • They have high density.
  • They have high melting and boiling points.
  • They are good conductors of heat and electricity.
  • They exhibit ductility and malleability because ion layers can slide over each other.

Hydrogen Bonds

A hydrogen bond is about 20 times weaker than a covalent bond. It is studied as a type of molecular interaction due to the polarity of the covalent bond. It occurs between positively charged hydrogen atoms and small, electronegative atoms such as oxygen, nitrogen, or fluorine. These bonds are responsible for water’s high boiling point.

Polarity of Covalent Bonds and Dipole Moment

In molecules like HF, the sharing of electrons is not equal because the atoms involved have different electronegativities. This results in a polar covalent bond.

Intermolecular Forces (Van der Waals Forces)

Intermolecular forces, also known as Van der Waals forces, are responsible for macroscopic properties such as boiling point, hardness, melting point, viscosity, etc. They are much weaker than intramolecular forces and can be overcome with a relatively low energy input.

London Dispersion Forces

London dispersion forces are responsible for the union between nonpolar atoms or molecules. Polar particles such as H2, O2, and N2, and even He, can be liquefied, which presupposes some attraction between them. London acknowledged that the motion of electrons in an atom can create an instantaneous dipole moment when the electron density is asymmetrically distributed.