Hydrogen Bonding - Practice Questions & MCQ

Hydrogen Bonding

Hydrogen bonds are strong forces which occurs when a hydrogen atom bonded to an electronegative atom approaches a nearby electronegative atom such as O, N, F, etc.. Greater the electronegativity of the atom will result in an increase in hydrogen-bond strength. The hydrogen bond is stronger intermolecular force, but it is weaker than a covalent or an ionic bond. Hydrogen bonds are responsible for holding together DNA, proteins, and other macromolecules.

Formation of Hydrogen Bond

A hydrogen bond is the electromagnetic attraction that occurs between a partially positively charged hydrogen atom attached to a highly electronegative atom and another nearby electronegative atom. A hydrogen bond is a type of dipole-dipole interaction; it is not a true chemical bond. This hydrogen bond attraction can occur between the different molecules (intermolecularly) or within different parts of a single molecule (intramolecularly).

Types of Hydrogen Bonding

There are two types of hydrogen bonding, i.e:

• Intermolecular Hydrogen Bonding: Intermolecular hydrogen bonding occurs when the H-atom of one molecule and an electronegative atom of another molecule are close to each other. For example,  hydrogen bond between the molecules of hydrogen fluoride. Intermolecular hydrogen bonding results into association of molecules. Thus, it increases the melting point, boiling point, solubility, etc.   

• Intramolecular Hydrogen Bonding: Intramolecular hydrogen bonding occurs the hydrogen atom and an electronegative atom of the same molecule. Intramolecular hydrogen bonding results in the cyclization of the molecules and prevents their association. Thus, the properties of these compounds like melting point, boiling point, etc. are usually low. For example, intramolecular hydrogen bonding is present in molecules such as o-nitrophenol, o-nitrobenzoic acid, etc.

• Formal charge is given by using the follwoing formula:

Formal charge = V - N - (1/2)B

V = Total number of valence electrons

N = Total number of lone pair of electrons

B = Total number of shared electrons or bonded electrons.

• In hypervalent ions like SO₂^-4 and PO₃^-4, the central atom has more than 8 electrons.

• Banana bonding is shown by boron hydride, i.e, diborane.

• Molecular solids have low heat of fusion.

• When the energy gap is very small, conduction occurs while the energy gap is large then no conduction occurs.

• C₂ molecule has no bonds but only bonds.

• The bond length of CO > CO⁺ because the bond order of CO is 3 and for CO⁺ is 3.5.