Tag: chemical bond and chemical equation

Assertion: The weakest of the forces between molecules are dispersion forces or London forces.
Reason: Dispersion forces or London forces represent the weak attractive forces that originate as a result of instantaneous dipoles induced in atoms or molecules.
Hence, both the assertion and reason are not correct.

In a dative bond, the shared pair of electrons come from the same atom. In $NH _{4}^{+}$ all the 4 valence electrons of N are bonded to the hydrogen atoms, thus it cannot act as an electron pair donor for the formation of dative bond.

The unique thing about the bonds in coordination compounds is that one of the atoms or ions donates both shared electrons. Thus, the bond is covalent coordinate bond.

Dative bond is present in the $\displaystyle PCl _5$ molecule.
In the solid state, $\displaystyle PCl _5$ molecule exists in the form of $\displaystyle [PCl _4]^+$ $\displaystyle [PCl _6]^-$
Dative bond is present in $\displaystyle [PCl _6]^-$ ion. The chloride ion is the donor atom and P atom is acceptor atom. The dative bond is also called co ordinate covalent bond.

A coordinate covalent bond is represented by an single arrow from donor to acceptor.
A coordinate bond is formed when one atom donates its pair of electrons to the other atom. For example, a lone pair of electrons on N atom of ammonia is donated to a proton to form ammonium ion with a coordinate bond between N and H.

 (A) $\displaystyle NH _4^+$ ion contains a dative bond (co-ordinate covalent bond) between $\displaystyle N$ atom and  $\displaystyle H$ atom.
$\displaystyle H _3N \rightarrow H^+$

(B) Bond angle increases when a bond is formed between $\displaystyle NH _3$ and $\displaystyle H^+$. In $\displaystyle NH _3$ molecule, due to repulsion between lone pair and bond pair of electrons, the bond angle decreases. When $\displaystyle NH _4^+$ ion is formed, lone pair is converted into bond pair. The inter electron repulsion decreases and bond angle increases.

(C) $\displaystyle NH _4^+$ ion has tetrahedral shape. $\displaystyle NH _3$ molecule has pyramidal shape.

(D) The type of hybridisation is not changed when bond is formed between $\displaystyle NH _3$ and $\displaystyle H^+$

$\displaystyle  NH^+ _4$  and $\displaystyle  H _3O^+$  have coordinate covalent bonds.
$\displaystyle  NH^+ _4$ is formed by a coordinate covalent bond between $\displaystyle  NH _3$  and $\displaystyle  H^+$.
$\displaystyle  H _3O^+$ is formed by a coordinate covalent bond between $\displaystyle  H _2O$  and $\displaystyle  H^+$. 

$\displaystyle {N} _{2}{H} _{3}^{+}$ contain a coordinate covalent bond.
$\displaystyle H-N=\underset{\displaystyle \underset{\displaystyle H}{\downarrow}}{N}^+-H$
The N atom is the donor atom and H atom is the acceptor atom.

The bonds present in  $\displaystyle K _4 [Fe(CN) _6]$ are ionic, covalent and coordinate covalent bonds. Ionic bonds are present between $\displaystyle K^+$ ion and $\displaystyle [Fe(CN) _6]^{4-}$ ion.
Covalent bonds are present in $\displaystyle C \equiv N$ ligand.
Co-ordinate covalent bonds are present between $\displaystyle Fe$ and $\displaystyle C$ and also in between $\displaystyle C$ and $\displaystyle N$.

In $\displaystyle ammonium $ ion $\displaystyle NH _4^+$ three $\displaystyle N-H$ bonds are covalent and one $\displaystyle N-H$ bond is coordinate covalent (dative). $Hydrogen$ atoms are situated at the corners of a tetrahedron as $\displaystyle N$ atom is $\displaystyle sp^3$ hybridised.