Chemical Bonds
Chemical bonds are defined as a set of interactions that take place in the electron shell of atoms, in order to join and form a molecule or a chemical stable compound.
In the study of adhesives, the role of chemical bonding is more important owing to its intermolecular forces. Both are directly responsible for providing the adhesive bond strength and the adhesion on the substrate. The chemical bonds are presented in both, the area of adhesion between the substrate and in the adhesive, as in the inner zone of the adhesive itself known as cohesion.
Chemical bonds can be divided into 3 groups: covalent bonds, ionic bonds, and metal bonds. Among them, the covalent bond is the one that takes place in the adhesive joints using organic adhesives based on polymers.
Covalent Bonds
Covalent bonds are defined as the union that occurs between two atoms by the sharing of two or more electrons in its outer layer, to form a stable molecule.
A clear example is the molecule of chlorine. Chlorine occurs in nature as a molecule composed of two atoms of chlorine. Chlorine atoms are linked by a covalent bond produced by the sharing of two electrons. During this process, two atoms join together to form one molecule, ignoring the molecular orbital theory. To explain it simply, we can say that two atomic orbits (Cl + Cl) combine to form a new molecular orbits (Cl2). The orbits are defined as regions of the atoms or molecules where the electrons are located.
In covalent bonds, two types of covalent bonds, polar covalent bond and non polar covalent bond, can arise.
Polar covalent bond is caused when one atom has stronger attraction of electrons to the nucleus. As a result, it produces a molecule with the negative and positive area (dipole). The polar covalent bond always occurs when the bond is between two different atoms. The degree of polarity of the molecule resulting from the covalent bond depends on the strength or attraction that attracts electrons to an atom, which is defined by the electronegativity. Examples of polar covalent bonds include water, isopropyl alcohol, etc.
Non polar covalent bond occurs when two atoms have the same force of attraction of electrons to the nucleus. Non polar covalent bond always occurs when the bond is between two atoms with equal or the same degree of electronegativity.
This article is reproduced from AdhesiveandGlue.com.