A covalent bond is a type of chemical bonding that occurs between 2 atoms when they share electrons in order to complete the last level. To understand chemical bonds, it is necessary to know how the electrons are distributed around the atom or the octet rule. The octet rule determines that the ions of the chemical elements have the tendency to complete their last energy levels with a number of 8 electrons, so that they acquire a very stable configuration.
Index
DIFFERENCE BETWEEN COVALENT AND IONIC BONDING
When the difference in electronegativity between the atoms is not large enough to produce a ionic bond. It is necessary that the difference in electronegativity between atoms is less than 1.7
In a ionic bondIn a covalent bond, electrons are transferred between one atom and another. In covalent bonding, electrons are shared. The 2 atoms bond through their electrons in the last orbital.
EXAMPLES OF COVALENT BONDS
We can distinguish between 2 types of substances with covalent bonds, the polar, non-polar and reticular molecular covalent bond. The difference is that in the reticular bond, the substances form crystalline networks of an indefinite number of atoms, similar to ionic compounds, with much stronger intermolecular bonds than in the molecular covalent bond (see properties of both in the following section).
OXYGEN MOLECULE. NON-POLAR COVALENT BOND.
The oxygen atoms are bonded together through a covalent bond to give an oxygen molecule, O2. Two of the last shell electrons are shared so that both have the full last shell, according to the following distribution:
Covalent bonds can be:
- simple: only 1 atom is shared, as in the case of hydrogen.
- double: 2 atoms are shared, as in the case of oxygen.
- triples: 2 atoms are shared, as in the case of nitrogen.
The bond in the oxygen molecule is covalent non-polar because the electrons are shared equally between the two oxygen atoms as there is no difference in electronegativity between them....
WATER MOLECULE. POLAR COVALENT BOND
In the water molecule the hydrogen will also have a slight positive charge because the other element pulls the bonding electrons more strongly. By having this slight positive charge, the hydrogen will be attracted to any negatively charged atoms. This type of bonding is called hydrogen bonding.
QUARTZ. LATTICE COVALENT BOND
Quartz represents another type of covalent bond, in this case reticular. Quartz, with the formula SiO2, has the characteristics of covalent substances, but is hard and has a high melting point. In this case, there are no individual molecules as in the case of the oxygen molecule or iodine, but three-dimensional structures of atoms linked by covalent bonds. Some compounds, such as silicon dioxide (quartz)of formula SiO2.
In quartz, each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms, forming an infinite three-dimensional lattice. To break the crystals, many covalent bonds have to be broken, hence their hardness and high melting and boiling points.
PROPERTIES OF COVALENT SUBSTANCES
Molecular covalent substances: Examples: oxygen, iodine. The properties of molecular covalent bonds are as follows:
- Low melting and boiling temperatures.
- They occur as a solid, liquid or gas under normal conditions of pressure and temperature (approx. 25 °C).
- They are soft in solid state.
- They are insulators of electric current and heat.
- Solubility: polar molecules are soluble in polar solvents and non-polar molecules are soluble in non-polar solvents (like dissolves like).
- Examples: carbon dioxide, benzene, oxygen, nitrogen.
Covalent lattices or reticular covalent substances: Some substances are linked by reticular covalent bonds that have the following properties:
- High melting and boiling points.
- Under normal conditions of pressure and temperature (approx. 25 °C) they are solids.
- They are very hard substances that are difficult to break.
- They are electrical insulators (except graphite).
- They are insoluble in both polar and non-polar substances.
- Examples: quartz, diamond.
EXAMPLES OF COVALENT BONDS
Water molecule (H2O), Ammonia (NH3), H2 (dihydrogen gas), O2 (oxygen gas), Cl2 (chlorine gas), Br2 (elemental bromine), N2 (nitrogen gas), CH4 (methane), C2H6 (ethane), S8 (rhombic sulphur), P4 (white phosphorus) and NF3 (nitrogen fluoride).