The Lewis structure of AsH3 shows nonbonding electron pair(s) on As.
A) 0
B) 1
C) 2
D) 3
The correct answer and explanation is :
The correct answer is B) 1.
Explanation:
Arsenic trihydride (AsH₃), also known as arsine, is a molecule in which arsenic (As) is bonded to three hydrogen (H) atoms. To understand the number of nonbonding electron pairs on arsenic in the Lewis structure, we need to consider its electron configuration, the valence electrons, and how they are distributed in the structure.
- Electron Configuration of Arsenic: Arsenic (As) belongs to Group 15 of the periodic table, so it has 5 valence electrons. These electrons will be involved in bonding with hydrogen atoms and may also form lone pairs.
- Bonding in AsH₃: In the Lewis structure, each hydrogen atom forms a single bond with arsenic. A single bond between arsenic and hydrogen consists of two electrons, one from arsenic and one from hydrogen. Since there are three hydrogen atoms, three pairs of electrons are used for bonding.
- Remaining Electrons: After forming three bonds with the hydrogen atoms, arsenic will have two remaining valence electrons. These two electrons cannot be shared with other atoms and will form a lone pair. Therefore, arsenic has one lone pair of electrons.
- Molecular Geometry: The molecular geometry of AsH₃ is similar to ammonia (NH₃), which has a trigonal pyramidal shape. The lone pair on arsenic causes a deviation from a perfectly planar structure, and the geometry is determined by the repulsion between bonding pairs and the lone pair.
- Final Answer: Arsenic, in this case, has one lone pair of electrons, so the correct answer is B) 1.
In summary, arsenic in AsH₃ has 5 valence electrons, 3 of which are involved in bonding with hydrogen, leaving 2 electrons that form a lone pair. Therefore, the number of nonbonding electron pairs on arsenic is 1.