the number of nonbonding electrons exceeds the number of bonding electrons in the lewis structure of which of the following molecules? I am having a problem with the Lewis structures.

HCN
NH3
H2O

please explain the structure
thank you so much

I can't draw Lewis structures on this forum; I suggest you google Lewis structure xxx where xxx is the molecule and look at those diagrams. You can count the non-bonding electrons.

To determine the number of bonding and nonbonding electrons in a molecule's Lewis structure, we need to follow a few steps:

Step 1: Count the valence electrons of each atom.
In the case of HCN, NH3, and H2O, we need to consider the valence electrons of hydrogen (H), carbon (C), nitrogen (N), and oxygen (O).
- Hydrogen (H) has 1 valence electron.
- Carbon (C) has 4 valence electrons.
- Nitrogen (N) has 5 valence electrons.
- Oxygen (O) has 6 valence electrons.

Step 2: Determine the total number of valence electrons in the molecule.
For HCN:
- H has 1 valence electron x 1 atom = 1 electron from hydrogen.
- C has 4 valence electrons x 1 atom = 4 electrons from carbon.
- N has 5 valence electrons x 1 atom = 5 electrons from nitrogen.
The total = 1 + 4 + 5 = 10 valence electrons.

For NH3:
- H has 1 valence electron x 3 atoms = 3 electrons from hydrogen.
- N has 5 valence electrons x 1 atom = 5 electrons from nitrogen.
The total = 3 + 5 = 8 valence electrons.

For H2O:
- H has 1 valence electron x 2 atoms = 2 electrons from hydrogen.
- O has 6 valence electrons x 1 atom = 6 electrons from oxygen.
The total = 2 + 6 = 8 valence electrons.

Step 3: Determine the central atom.
The central atom is typically the least electronegative atom or the one with the lowest valence electrons. In this case, it would be carbon (C) for HCN, nitrogen (N) for NH3, and oxygen (O) for H2O.

Step 4: Connect the atoms using single bonds.
In HCN, carbon will be the central atom. It will form a single bond with nitrogen. Hydrogen will form a single bond with carbon.
In NH3, nitrogen will be the central atom. It will form three single bonds with hydrogen.
In H2O, oxygen will be the central atom. It will form two single bonds with hydrogen.

Once you have drawn the Lewis structures, you can calculate the number of bonding and nonbonding electrons.

For example:
- In HCN, carbon and nitrogen form a triple bond, resulting in 3 bonding electrons. Carbon has no nonbonding electrons, while nitrogen has 3 nonbonding electrons.
- In NH3, nitrogen forms three single bonds with hydrogen, resulting in 3 bonding electrons. Nitrogen has 1 nonbonding electron.
- In H2O, oxygen forms two single bonds with hydrogen, resulting in 2 bonding electrons. Oxygen has 2 nonbonding electrons.

So, in this case, the molecule with the number of nonbonding electrons exceeding the number of bonding electrons is NH3.