draw a lewis structure for ammonia, nh3 . include all hydrogen atoms and show all unshared pairs and the formal charges, if any. assume that bonding follows the octet rule.
The Correct Answer and Explanation is :
Lewis Structure for Ammonia (NH₃)
To draw the Lewis structure for ammonia (NH₃), follow these steps:
- Count the total number of valence electrons:
- Nitrogen (N) has 5 valence electrons.
- Each hydrogen (H) has 1 valence electron, and there are three hydrogens: ( 3 \times 1 = 3 ).
- Total: ( 5 + 3 = 8 ) valence electrons.
- Determine the central atom:
- Nitrogen is less electronegative than hydrogen, so it will be the central atom.
- Connect the atoms:
- Draw single bonds between the nitrogen and each of the three hydrogen atoms. Each bond uses 2 electrons:
- Thus, ( 3 \text{ bonds} \times 2 \text{ electrons} = 6 ) electrons used.
- Place remaining electrons:
- From the total of 8 electrons, 6 are used in bonds, leaving 2 electrons.
- These remaining electrons are placed as a lone pair on the nitrogen atom.
- Check the octet rule:
- Nitrogen now has 3 bonds (3 electrons from bonds) + 2 lone pair electrons = 5 electrons around it, which satisfies the octet rule for nitrogen as it can have a stable configuration with 5 valence electrons (following the 5-electron rule).
- Formal charge calculation:
- Formal charge can be calculated using the formula:
[
\text{Formal Charge} = \text{Valence Electrons} – (\text{Non-bonding Electrons} + \frac{1}{2} \times \text{Bonding Electrons})
] - For nitrogen:
[
\text{Formal Charge of N} = 5 – (2 + \frac{6}{2}) = 5 – (2 + 3) = 0
] - For each hydrogen:
[
\text{Formal Charge of H} = 1 – (0 + \frac{2}{2}) = 1 – 1 = 0
]
The final Lewis structure for NH₃ is:
H
|
H - N - H
|
(lone pair)Explanation
In the Lewis structure of ammonia, nitrogen is surrounded by three hydrogen atoms and one lone pair of electrons. Each hydrogen atom forms a single bond with nitrogen, contributing a total of 6 electrons to the bonding framework. The remaining two electrons are held as a lone pair on nitrogen.
The formal charges for all atoms in NH₃ are zero, indicating that this is a stable configuration. Ammonia’s structure follows the octet rule and illustrates that nitrogen can achieve a stable electronic arrangement while bonded to three hydrogens, all of which have complete outer shells with two electrons in their 1s orbitals. This structure helps explain ammonia’s molecular shape (trigonal pyramidal) and its chemical behavior, such as its ability to act as a Lewis base, donating a lone pair to form coordinate covalent bonds with other atoms or molecules.