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Define electronegativity - Leaving Cert Chemistry - Question 11 - 2014
Question 11
Define electronegativity. Ammonia (NH₃) and silane (SiH₄) are small molecules, each of which has four electron pairs in the valence shell of the central atom. Acco... show full transcript
Worked Solution & Example Answer:Define electronegativity - Leaving Cert Chemistry - Question 11 - 2014
Step 1
Step 2
Account for the difference in bond angle between the two molecules.
Answer
In ammonia (NH₃), the lone pair of electrons exerts greater repulsion than a bond pair of electrons, leading to a bond angle of 107.3°. In silane (SiH₄), there are four bond pairs and no lone pairs, resulting in a bond angle of 109.5° due to the symmetrical distribution of electron pairs.
Step 3
Use electronegativity values to determine which bond is more polar.
Answer
The electronegativity values are approximately: N = 3.04 and Si = 1.90. The difference between N and H is greater (3.04 - 2.20 = 0.84) than that between Si and H (1.90 - 2.20 = -0.30). Therefore, the N-H bond in ammonia is more polar than the Si-H bond in silane.
Step 4
Which of the two substances has hydrogen bonding between its molecules? Justify your answer.
Answer
Ammonia (NH₃) has hydrogen bonding between its molecules due to the presence of hydrogen bonded to a small, highly electronegative element (nitrogen). This strong intermolecular force is not present in silane (SiH₄).
Step 5