Draw the Lewis structure for AsH3. Answer the following questions for the Lewis structure for AsH3 given that arsenic obeys the octet rule. 1. How many double bonds exist in this structure? 2. How many single bonds exist in this structure? 3. How many bonds does the arsenic atom form? 4. How many electrons surround the arsenic atom? 5. How many lone pairs are around the arsenic atom? 6. How many bonds does each hydrogen atom form? 7. How many lone pairs are around each hydrogen atom? 8. How many electrons surround each hydrogen atom?
Draw the Lewis structure for AsH3. Answer the following questions for the Lewis structure for AsH3 given that arsenic obeys the octet rule. 1. How many double bonds exist in this structure? 2. How many single bonds exist in this structure? 3. How many bonds does the arsenic atom form? 4. How many electrons surround the arsenic atom? 5. How many lone pairs are around the arsenic atom? 6. How many bonds does each hydrogen atom form? 7. How many lone pairs are around each hydrogen atom? 8. How many electrons surround each hydrogen atom
The Correct Answer and Explanation is:
Lewis Structure of AsH₃ (Arsine)
To draw the Lewis structure for arsine (AsH₃), follow these steps:
- Count total valence electrons:
- Arsenic (As): Group 15 → 5 valence electrons
- Hydrogen (H): Group 1 → 1 valence electron × 3 = 3
- Total = 5 (As) + 3 (H) = 8 valence electrons
- Create the skeletal structure:
Place arsenic in the center, with three hydrogen atoms bonded to it:H | H - As - H - Distribute remaining electrons to complete the octet for arsenic.
- Each As–H bond uses 2 electrons × 3 = 6 electrons
- Remaining electrons = 8 – 6 = 2 electrons
- Place the remaining 2 electrons (1 lone pair) on As
The final Lewis structure looks like this:
H
|
H — As — H
..
(The two dots above As represent a lone pair.)
Answers to the Questions:
- Double bonds: 0
- Single bonds: 3
- Bonds As forms: 3
- Electrons surrounding As: 8 (6 from bonds, 2 from lone pair)
- Lone pairs on As: 1
- Bonds each H forms: 1
- Lone pairs on each H: 0
- Electrons surrounding each H: 2
Explanation
The Lewis structure of arsine (AsH₃) follows the basic principles of electron counting and the octet rule. Arsenic, in Group 15 of the periodic table, has 5 valence electrons. Each hydrogen atom contributes 1 valence electron, giving a total of 8 valence electrons for the entire molecule. To construct the Lewis structure, arsenic is placed in the center with three hydrogen atoms bonded around it. Each As–H bond uses 2 electrons, for a total of 6 electrons in bonding. This leaves 2 electrons, which are placed as a lone pair on the arsenic atom.
Arsenic forms three single bonds with hydrogen atoms, meaning there are no double bonds in the structure. Since each bond consists of 2 electrons, the arsenic atom shares 6 electrons with hydrogen and retains one lone pair (2 electrons), making a total of 8 electrons around it, thus satisfying the octet rule. Arsenic forms 3 bonds and has 1 lone pair.
Hydrogen, which only requires 2 electrons to satisfy its duet rule, forms one single bond with arsenic and shares those 2 electrons with As. Therefore, each hydrogen has 0 lone pairs and is surrounded by 2 electrons, fulfilling its stability requirement.
This Lewis structure reflects a trigonal pyramidal molecular geometry due to the lone pair on arsenic, which slightly repels the bonded pairs, reducing the bond angles from the ideal 109.5° of a tetrahedral shape. Understanding the Lewis structure of AsH₃ is essential for predicting its geometry, polarity, and chemical behavior in reactions.
