Formation of Ammonia Boron Trifluoride

Ammonia Boron Trifluoride or Trifluoroborane ammonia has a molecular formula of BF3H3N. Its molecular weight is 84.84 u. It has coordinate bonding which is sometimes also known as dative covalent bonding. In a coordinate bond, both electrons are contributed from the same atom. The other atom does not share its electron, it is only a one-sided sharing. A dative bond can be represented by drawing an arrowhead pointing from donor to acceptor atom.

Examples of dative or coordinate bonds are Ammonia and Hydrogen chloride, formation of Ammonia Boron Trifluoride,  ammonium chloride, nitric acid, carbon monoxide, etc.

Types of chemical bonds

Every element has a different valence shell electronic configuration because of which they combine in different ways to form compounds. So, there are various types of chemical bondings possible between atoms to form molecules. 

On the basis of bond strength, bonds can be classified as strong bonds and weak bonds.

Strong bonds can be further subdivided as Ionic bonds, Covalent bonds, Coordinate bonds, and Metallic bonds.

Weak bonds can be categorised as Hydrogen bonds and van der Waals’ interaction.

Ionic bonds: 

It is formed by the complete transfer of electrons between atoms. One atom loses electrons to form cations whereas one atom gains them and forms anions so, we can simply say that the bond is formed between ions that attract each other via electrostatic forces of attraction. Examples are NaCl, MgCl2, etc.

Covalent bonds:

It is formed when the sharing of electrons takes place between atoms. Each of them contributes one electron to the electron pair needed to form a bond. Due to this, each of the atoms acquires a stable noble gas configuration. Examples are H2, Cl2, CH4, etc.

Coordinate covalent bonds:

These are formed when a covalent bond forms between 2 atoms by sharing 2 electrons, both of them coming from the same atom. Usually, the lone pair of one of the atoms is involved in the dative or coordinate bonds. Examples are NH4+, NH3→BF3, etc.

Metallic bonds:

Metallic bonds join the bulk of metal atoms.  The electron sea model describes metallic bonding. It consists of atomic core and valence electrons. Metallic bonds arise because of electrostatic forces between the atomic core and valence electrons. Examples are a sheet of aluminium foil, copper foil, etc.

Hydrogen bonds:

These bonds are formed when hydrogen is bonded covalently to an electronegative atom such as nitrogen, oxygen, or nitrogen.  An example is a water molecule. Here, the hydrogen atom of one atom has a partial positive charge and the oxygen atom of another molecule has a partially negative charge, so electrostatic attraction takes place.

Van der Waals interactions:

These attractions take place between any 2 or more molecules and depend on slight changes in the electron distribution, which are not always symmetrical around an atom. Examples are London dispersion forces, dipole-dipole forces, etc.

Reaction between ammonia and boron trifluoride

BF3  is an electron-deficient compound. It violates the octet rule as the boron atom doesn’t have a noble gas/ inert gas structure around itself. Even though it has room for four pairs, the boron still has only three pairs of electrons at the bonding level.

Ammonia is an electron-rich compound. The lone pair on the nitrogen atom of the ammonia molecule can help boron trifluoride in overcoming the deficiency of electrons. Due to this reason, coordinate bonding occurs, leading to the formation of the Ammonia Boron Trifluoride compound.

When the nitrogen atom donates a pair of electrons so that the boron can share, the boron ends up getting an octet. Both the atoms become electronically saturated. Apart from that, a pair of non-bonding electrons becomes bonding. They get delocalized over 2 atoms and their energy gets lowered. 

BF3 + ⠅NH3   →    F3B←⠅NH3

This reaction can be explained by using the concept of Lewis acids and Lewis bases. Lewis acid is a substance that can accept a pair of electrons, forming a covalent bond. On the other hand, a Lewis base is one that donates electrons to form covalent bonds. 

Boron trifluoride is a Lewis acid because it is electron deficient. Ammonia is Lewis base because it has a lone pair of electrons. As no involvement of hydrogen ions is there, it is still an acid-base reaction according to Lewis concept.

Conclusion 

We know that every element has a different valence shell electronic configuration, so they combine differently to form chemical bonds.

There are different types of chemical bonds such as ionic bonds, covalent bonds, coordinate bonds, metallic bonds, hydrogen bonds, and van der Waals interactions. Hydrogen bonds and van der Waals interactions are weak bonds whereas all the others i.e., ionic bonds, covalent bonds, coordinate bonds, and metallic bonds are strong bonds. 

The case of the formation of Ammonia Boron Trifluoride was considered. It was seen that it was an acid-base reaction by the concept of Lewis acids and bases. Boron trifluoride was a Lewis acid whereas the Lewis base was ammonia because of the presence of lone pairs on the nitrogen atom. 

Boron trifluoride is electron deficient. Ammonia is rich in electrons. So, the nitrogen atom of ammonia can donate a pair of electrons to the boron atom of Boron trifluoride. Due to this, a pair of non-bonding electrons becomes bonding and gets delocalized over 2 atoms. Since it is only one-sided sharing by a nitrogen atom, it is a dative or coordinate bond. The energy gets lowered and Ammonia Boron Trifluoride is formed.