Q14.36 P - Chemistry: Molecular Nature Of Matter And Change

Question

Draw Lewis structures for the following compounds and predict which member of each pair will form hydrogen bonds:

(a) NH₃ or AsH₃    

 (b) CH₄ or H₂O

Step-by-Step Solution

Answer

(a) $N{H}_3$ will form hydrogen bonds.

(b) $H_{2}O$will form hydrogen bonds.

Step 1: Lewis structure

Lewis structure, also termed Lewis-dot structure, is a structural representation of a molecule that shows bonding between the lone pairs of electrons and atoms that occur inside the molecule.

To draw the Lewis dot structure, firstly, we have to calculate the total number of valence electrons in the molecule and identify the central atom.

 In the second step, draw the skeleton structure having a single bond between the atoms and subtract two electrons from valence electrons for every single bond.

At last, distribute the remaining electrons, so that all atoms except hydrogen complete their octets.

Step 2: Hydrogen bonding

Hydrogen bonding refers to the interaction of a hydrogen atom with an electronegative element, mainly fluorine, oxygen and nitrogen.

A hydrogen bond is weaker than a covalent or ionic bond, but it is much stronger than the van der Waal’s interaction force between the atoms. It is mainly of two types.

Intermolecular hydrogen bonding: The interaction between the hydrogen atoms of one molecule and an electronegative element of neighbouring molecules is known as intermolecular hydrogen bonding.

Intramolecular hydrogen bonding: The interaction between the hydrogen atoms and an electronegative element within similar molecules is known as intramolecular hydrogen bonding.

Step 3: Predicting the molecule that forms a hydrogen bond and drawing its Lewis structure

(a) $N{H}_3$ will form hydrogen bonds. As we move down the periodic table, the group electronegativity decreases. Therefore, nitrogen is a more electronegative element than arsenic and forms intramolecular hydrogen bonds more easily than arsenic.

(b) $H_{2}O$ will form hydrogen bonds, because oxygen is more electronegative than carbon, therefore easily forming intramolecular hydrogen bonds.