Coordinate Covalent Bond vs Covalent Bond
As proposed by the American chemist G.N.Lewis, atoms are stable when they contain eight electrons in their valence shell. Most of the atoms have less than eight electrons in their valence shells (except the noble gases in the group 18 of the periodic table); therefore, they are not stable. These atoms tend to react with each other, to become stable. Thus, each atom can achieve a noble gas electronic configuration. Covalent bonds are a major type of chemical bonds which connect atoms in a chemical compound.
Polarity arises due to the differences in electronegativity. Electronegativity gives a measurement of an atom to attract electrons in a bond. Usually Pauling scale is used to indicate the electronegativity values. In the periodic table, there is a pattern as to how the electronegativity values are changing. From left to right through a period, the electronegativity value increases. Therefore, halogens have larger electronegativity values in a period, and group 1 elements have comparatively low electronegativity values. Down the group, the electronegativity values decrease. When two of the same atom or atoms having the same electronegativity form a bond between them, those atoms pull the electron pair in a similar way. Therefore, they tend to share the electrons and this kind of bonds is known as non polar covalent bonds.
When two atoms having similar or very low electronegativity difference, react together, they form a covalent bond by sharing electrons. Both atoms can obtain the noble gas electronic configuration by sharing electrons in this way. Molecule is the product resulted by the formation of covalent bonds between atoms. For example, when the same atoms are joined to form molecules like Cl2, H2, or P4, each atom is bonded to another by a covalent bond.
Coordinate Covalent Bond
This is also a type of covalent bond where the two electrons in the bond are only donated by a single atom. This is also known as a dative bond. This type of covalent bonds is formed when a Lewis base donates an electron pair to a Lewis acid. Therefore, this can also be explained as a bond between a Lewis acid and a Lewis base. In theory, to show the donating atom and non- donating atom, we put positive charge for the donating atom and negative charge for the other atom. For example, when ammonia donates the lone electron pair of nitrogen to the Barium of BF3, a coordinate covalent bond results. After formation, this bond is similar to a polar covalent bond and cannot distinguish as a separate bond although it has a separate name.
What is the difference between Covalent Bond and Coordinate Covalent Bond?
• In a covalent bond, both atoms are contributing same number of electrons to the bond, but in a coordinate covalent bond, two electrons are donated by a single atom.
• In a covalent bond, the electronegativity difference between the two atoms can be zero or a very low value, but in coordinate covalent bond, type of a polar covalent bond is forming.
• For a coordinate covalent bond to form, an atom in the molecule should have a lone pair.