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Chemistry tutorial: Basics: Chemical bonds

There are several types of bonds that may occur between atoms. The basic three types are covalent, ionic and metallic bond.

Covalent bonds are based on the formation of shared electron pairs. When, for example, an atom has the oxidation state of -1, and the other has +1, between the atoms a creation of electron pairs (i.e. covalent bonds) can occur, because of achieving greater stability. Covalent bonds are typical for atoms between which there is a lower electronegativity difference. In addition to the mentioned single covalent bond, there are also double (two electron pairs) and triple (three electron pairs) covalent bonds.

Ionic bond is a bond that connects elements between which there is a greater electronegativity difference. For example, a bond between the alkali metals and halogens is a typical ionic bond. The ionic bond isn't based on formation of shared electron pairs, but the electron transition from one atom to another. Because of that, in ionic compounds, positively charged (cations) and negatively charged (anions) particles can be distinguished. The charge of particles is caused by atoms that lose electrons (because of that, they have more protons than electrons and are therefore positively charged), and atoms that accept electrons (because of that they have more electrons than protons, and are therefore negatively charged).

Metallic bond is a bond that forms between metallic atoms, and is based on the interaction of delocalized electrons that come from metal atoms and the nuclei of these same metallic atoms. Some of the properties related to the metallic bond are good electrical and thermal conductivity. The metallic bond should be seen as a collective phenomenon, in cases of larger clusters of metallic atoms, and should be distinguished from the bonds between individual metallic atoms in some metal ions. A typical example of such ions is Hg22+.

Concerning the bonds between molecules, it is important to mention van der Waals forces and the hydrogen bond.

Van der Waals forces are relatively weak forces that occur between nonpolar molecules. These forces are much weaker than any of the bonds that exist between atoms. They form due to the movement of electrons along the bonds between the atoms of molecules, whereby in certain moments, positive and negative charge centers form in the molecules, so that one end of the molecule is slightly positive and the other is slightly negative. Because of these charges that form in short periods of time, weak attractions between molecules are formed, which are known as van der Waals forces.

Hydrogen bond is a bond that occurs in molecules in which the hydrogen atom is bound to an atom with higher electronegativity (such as oxygen, nitrogen, fluorine, etc.). The atom with the greater electronegativity attracts the electron from the hydrogen atom to the extent that hydrogen becomes the center of the positive charge, while the atom with greater electronegativity becomes the center of the negative charge. Therefore, a bond is formed between the hydrogen atom of one molecule and the atom with greater electronegativity located in another molecule, and this phenomenon is known as the hydrogen bond. As a standard example, we can mention water, H2O, in which hydrogen bonds exist between the hydrogen atoms of one molecule of water, and the oxygen atoms within other water molecules.

chemistry tutorials - chemical bonds

On the picture above, one can see different types of chemical bonds. Type A is an ionic bond between one chlorine and one sodium atom. Type B is a covalent bond between two chlorine atoms. Type C is a hydrogen bond which exists between the hydrogen atom of one water molecule, and the oxygen atom of another water molecule.


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