Nitroxyl (HNO); How to Draw Lewis Structure, Molecular Geometry, Hybridization, And VSPER Theory

The HNO molecule is commonly named Nitroxyl. It is also known as the conjugate base of nitroxide anion (NO^–). It is most commonly present in the gas phase.

This compound consists of three atoms bonded with each other through one double and one single bond. It contains three lone pairs of electrons. One lone pair of electrons is on the nitrogen atom, and the other two are present on the oxygen atom.

Lewis Dot Structure of HNO

Lewis structure is also called the electron dot structure or dot and cross structure. The Lewis dot structure of it contains one single and one double bond. One single bond is between hydrogen and nitrogen atoms.

One double bond is between nitrogen and oxygen atoms. The Lewis dot structure of HNO nitrogen contains one electron pair while oxygen contains two pairs of electrons. 

                  

Importance of Lewis Structure

A Lewis structure is the pictorial representation of bond formation in a molecule. It helps us to understand the valence electrons and the arrangement of atoms in the molecule.

Steps to Draw the Lewis Dot Structure of HNO

There are the following steps to drawing the Lewis structure.

1. Count Valance Electrons

The valence electrons of the hydrogen atom

Hydrogen is an element of group A1 in the periodic table. The Atomic Number of Hydrogen is= 1. 

You can see in the image that hydrogen has one valence electron.

The valance electrons of a nitrogen atom

 

Nitrogen is an element of group A5 in the periodic table. 

You can see in the image; that nitrogen has a five-valence electron.

The oxygen atom’s valence electrons

Oxygen is an element of group A6 in the periodic table.

You can see in the image that oxygen has six valence electrons.

Now, you can find the total number of valence electrons by adding up the valence electrons of all three atoms:

Valence electrons of one hydrogen atom=1

valence electrons of one nitrogen atom=5

valance electron of one oxygen atom = 6

Total valence electrons in HNO =1+5+6=12

 

2. Determine the Central Atom of HNO:

As per the rule;

The Atom with the least electronegative value should be the central atom of the molecule. Nitrogen has less electronegative value than oxygen. So, nitrogen will be the central atom of the molecule.

Although hydrogen is less electronegative than oxygen and nitrogen, it cannot be the central atom because the central atom should bond with at least two other atoms. Yet hydrogen has only one electron in its last shell.

It cannot make more than one bond. So, nitrogen should be the central atom in the Lewis dot structure of HNO. And hydrogen atoms should place in an outside position of the molecule. 

                   

3. Put electron pairs between the atoms to form a chemical bond

When you put one electron pair between hydrogen and carbon and one electron pair between nitrogen and oxygen. A chemical bond is formed between them. Now the HNO molecule has the following structure.

This shows that all these atoms are chemically joined in the molecule.

4. Complete the octet or duplet of atoms (stabilize the atoms)

In the above structure of the molecule, you can see that hydrogen has two electrons. Hydrogen completes its duplet.

Now you have to complete the octet of oxygen. Put three more electron pairs around the oxygen atom. Oxygen has 8 electrons in its outer shell. Thus, it is stable.

Total valence electrons in the HNO molecule are twelve. We have used only 10 electrons. The remaining two electrons are placed on the central atom i.e. nitrogen.

5. If the Octet of the central atom is not complete, Shift electrons pair to form a chemical bond

Nitrogen is not stable as it has six electrons in its outer shell. It has to complete its octet. Thus, an electron pair is shifted from oxygen to form a chemical bond.

You can see in the image that the electrons pair is shifted from oxygen to stable the nitrogen atom.

In the above image, nitrogen has completed its octet. Now, all atoms are stable.

6. Check the stability by calculating the formal charge

We can calculate the formal charge on an atom by the following formula;

Formal charge = valance electrons -nonbonding electrons -bonding electrons/2

Hydrogen Atom

Valence electron = 1

Bonding electrons = 2

Nonbonding electrons = 0

 Nitrogen Atom

Valence electrons = 5

Bonding electrons = 6

Nonbonding electrons = 2

Oxygen Atom

Valence electrons = 6

Bonding electrons = 4

Nonbonding electrons = 4

Atom		Valence electrons		(Bonding electrons)/2		Nonbonding electrons		Formal charge
H	=	1		2/2	–	0	=	0
N	=	5		6/2	–	2	=	0
O	=	6		4/2	–	4	=	0

You can see in the table that each atom in HNO has zero formal charges. It means there is no need for change in the structure.

In the molecule, each bond pair represent a bond. The lone pair of electrons present on the Nitrogen atom remains the same. It does not involve bond formation. So, the given structure is the final Lewis structure for the HNO molecule.                   

Hybridization of HNO

Lewis dot structure of the molecule consists of one hydrogen, one nitrogen, and one oxygen atom. Hydrogen contains one electron; nitrogen contains 7 electrons; oxygen contains 8.

In the Lewis structure, oxygen and nitrogen are SP² hybridized. In comparison, hydrogen is SP³ hybridized.

• One double bond is formed between oxygen and nitrogen due to unhybridized ‘P’ orbitals.
• One single bond is formed between hydrogen and nitrogen by SP^3__ SP²
• The other single bond is formed between oxygen and nitrogen by SP^2__SP²

Molecular Geometry and Shape of HNO

A molecule’s molecular geometry helps us understand the three-dimensional structure, arrangement of atoms in a molecule, and its shape. Suppose we know the molecular geometry of a molecule. Then, it would be easy to study a molecule’s reactivity, polarity, and biological activity.

Its molecule has three atoms, i.e., hydrogen, nitrogen, and oxygen. A lone pair of electrons is present on the nitrogen atom. According to VSEPR theory, the lone pair repels the other bond pair. Thus, bent geometry is formed.

Determine the Geometry by VSEPR Theory:

Valance shell electron pair repulsion theory is used to determine the molecular geometry of a molecule. This theory explains that the valance electrons pair surround the atom and arrange themselves so that they face the least repulsion from each other. VESPER theory explains geometry in the form of AXE notation.

The AXE notation is used to determine the molecular geometry of a molecule.

In AXE notation

• ‘A’ denotes the central atom in a molecule
• ‘X’ denotes atoms connected to the central atom, and
• ‘E’ denotes the number of lone pairs on the central atom.

In HNO molecule

• ‘A’ stands for nitrogen.
• ‘X’ stands for two atoms, i.e., hydrogen and oxygen and
• ‘E’ stands for one because one lone pair of electrons is present on the nitrogen atom in the HNO molecule

HNO molecule contains the AX₂E₁ type of notation. Thus, it has bent geometry.

The Bond Angle of HNO

As the Lewis structure of the HNO molecule has trigonal Bent geometry, the bond angle in HNO is 120^o.

Polarity of HNO

Polarity is the charge distribution over the atom joined by a bond within a molecule. The charge appears on an atom due to electronegativity difference. The bond will be polar when the electronegativity difference is more than 0.4.

However, the electronegativity difference between hydrogen and nitrogen is more than 0.4, which means that the bond is polar. Thus, the HNO molecule is polar.

Properties of HNO

• The molar mass is 31 g/mol.
• The bond dissociation energy for the HNO molecule is 49.5 kcal/mol.
• The heat capacity for the molecule is 33.9 JK^–
• HNO molecule is acidic.
• It is polar and soluble in water.
• It is more reactive and less stable.

Conclusion

• Its Lewis dot structure contains one single and one double bond.
• It also contains three lone pairs of electrons. One is present on the nitrogen atom, and the other two are present on the oxygen atom.
• HNO molecule is SP² hybridized with a bond angle of 120^o.
• It has bent molecular geometry.
• It is a polar substance and soluble in water.

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