What are covalent bonds made of?

A molecule [moleˈkyːl] (older also: Molecule [moˈleːkəl]; from lat. molecular, "Small mass") is a particle that consists of two or more connected atoms, which are connected by covalent bonds. Molecules are the smallest particles that have the properties of the underlying substance. There are molecules that are made up of a single element (O2, N2, P4 and much more m), but most of the molecules are compounds of non-metals with one (or more) other non-metals or semi-metals. A somewhat larger group of atoms of the same type is called a cluster.

Type of bond in molecules

In molecules, the connected atoms hold together via shared electron pairs. Such bonds are also called atomic bonds, electron pair bonds or covalent bonds. Even if the individual atoms do not have full elementary charges, i.e. are not present as ions, partial charges can occur due to asymmetrically distributed binding electron pairs. The atomic bonds are therefore divided into:

  • Non-polar atomic bond (covalent bond) - the difference in the electronegativity of the bond partners is 0. Strictly speaking, this type of bond only occurs with elemental molecules, i.e. with molecules that are composed of only one type of atom. In a broader sense, however, bonds between atoms (e.g. between C and H) are also understood as covalent bonds whose difference in electronegativity is greater than 0 and less than 0.4.
  • polar binding - the difference in the electronegativity of the binding partners is greater than 0.4 and less than 1.7.

Intermolecular forces (sorted by decreasing strength)

Various forces can act between the molecules, which can affect, for example, the boiling and melting points and the solubility properties:


The structure of a molecule can be described in different ways. Because molecules are not visible in the real world and so the molecules must be represented by spheres (just like the atoms).

The empirical formula is suitable for simple molecules, especially inorganic molecules, e.g. H2O for water or NH3 for ammonia. It contains the atomic symbols of the types of element contained in the molecule, the number of which is indicated by an index (the subscript). The effect of intermolecular forces is also dependent on the spatial structure of the molecules in the case of smaller molecules. The VSEPR theory is used to describe this structure.

In the case of more complex molecules, such as those mainly found in organic chemistry, a molecular formula often does not provide a sufficient description, since there can be different molecules with the same molecular formula (isomers). Therefore the structural formula is used, which shows the structure graphically.

In some cases, with mirror-inverted molecules, the enantiomers, the structural formula does not provide sufficient information about the structure that is effective to the outside world. Fischer and Haworth projections are used here.

In the case of highly complex molecules such as proteins or polymeric carbohydrates, the spatial representation plays an even greater role.

Attempts are made to design dome models for molecules and to achieve spatial representations through coloring. The blood pigment hemoglobin provides an example of a three-dimensional model of highly complicated biomolecules: Depending on the level, one speaks of the primary structure (defined in the case of proteins by the sequence of amino acids), the secondary structure (folding into a helix or a sheet), the tertiary structure ( Unfolding of the secondary structure into spheres or fibers) and the quaternary structure. (see: protein)

See also

Categories: Chemistry | Chemical bond | Atomic physics