Write the question and answers

QUESTION 2 NOV 2013

2.1 Define the term covalent bond. A covalent bond is a chemical bond formed when two atoms share one or more pairs of electrons.

2.2 Draw Lewis structures for:

2.2.1 $\text{CH}_4$ The central carbon atom forms single bonds with four hydrogen atoms. There are no lone pairs on the central carbon atom.

2.2.2 $\text{NH}_3$ The central nitrogen atom forms single bonds with three hydrogen atoms and has one lone pair of electrons.

(The lone pair on the nitrogen atom is represented by the two dots.)

2.3 Write down the number of lone pairs of electrons on the central atom in $\text{CH}_4$. $\boxed{\text{0}}$

2.4 Which ONE of the molecules in QUESTION 2.2 can form a dative covalent bond? $\text{NH}_3$ can form a dative covalent bond by donating its lone pair of electrons from the nitrogen atom. $\boxed{\text{NH}_3}$

2.5 Write down the shape of the $\text{NH}_3$ molecule. $\boxed{\text{Trigonal pyramidal}}$

2.6 Explain why $\text{CH}_4$ is a non-polar molecule, while $\text{NH}_3$ is a polar molecule. Step 1: Analyze bond polarity and molecular shape for $\text{CH}_4$. In $\text{CH}_4$, the C-H bonds are slightly polar due to a small electronegativity difference. The molecule has a symmetrical tetrahedral shape.

Step 2: Determine the overall polarity of $\text{CH}_4$. The four C-H bond dipoles are identical in magnitude and symmetrically arranged, causing them to cancel each other out. This results in a net dipole moment of zero, making $\text{CH}_4$ a non-polar molecule.

Step 3: Analyze bond polarity and molecular shape for $\text{NH}_3$. In $\text{NH}_3$, the N-H bonds are polar due to the significant electronegativity difference between nitrogen and hydrogen. The molecule has a trigonal pyramidal shape, and the nitrogen atom has one lone pair of electrons.

Step 4: Determine the overall polarity of $\text{NH}_3$. Due to the trigonal pyramidal shape and the presence of the lone pair, the N-H bond dipoles do not cancel each other out. This results in a net dipole moment, making $\text{NH}_3$ a polar molecule.