HCl; How to Draw Lewis Structure, Molecular Geometry, Hybridization and MOT Diagram

HCl is an inorganic chemical and it is a very corrosive acid and has a pungent and irritating smell. It is viscous and colourless. Its chemical formula is HCl, also known as hydrogen chloride or muriatic acid. It is a simple diatomic molecule. The bond between hydrogen and chlorine is polar covalent as chlorine is more electronegative than hydrogen i.e. their electronegativity difference is 0.9 ( hydrogen has an electronegativity of 2.1 and chlorine has 3.0). The physical properties of  HCl such as density, boiling point, pH, etc depend on the molar concentration of HCl.

Facts About HCl

• Hydrogen chloride is an inorganic acid and is mostly in gaseous form.
• The hydrogen chloride or hydrochloric acid chemical formula is HCl.
• Lewis structure of HCl contains only one H-Cl bond and there is no charge on HCl Lewis structure as it is a neutral molecule.
• There is one electron on Hydrogen and seven electrons in the valence shell of the chlorine atom.
• It is colourless gas of strong odour.
• Can be released from volcanoes.

Steps Of Drawing Lewis Structure Of  HCl

There are several steps to follow when we draw Lewis’s structure. Because HCl is a simple molecule with no charge on it, so we have to follow some of the following steps while drawing its Lewis structures.

• Find the total number of electrons of the valence shell of hydrogen and chlorine atom
• Find the total number of bond pairs and lone pairs
• Select the central atom
• Mark lone pairs on atom
• Mark charge on an atom if any
• Check the stability and minimize the charge by converting lone pairs to bonds to obtain the best Lewis structure

Total Number Of Electrons Of The Valence Shell Of HCl Molecule

There are only two elements in hydrogen chloride; hydrogen and chlorine. Since hydrogen belongs to group 1A, so it has one valence electron and chlorine belongs to group 7A so it has seven electrons in its last shell (valence shell).

• Valence electron shared by hydrogen atom =1*1=1
• Valence electron shared by chlorine atom =7*1=7
• Total valence electron =7+1=8

Total Valence Electron Pairs

The value of total electron pairs can be determined by dividing the total number of valence electron pairs by 2. As we have a total of 8 electrons in the valence shell of the HCl molecule, so by dividing it by 2.

Total number of electron pairs = total valence electrons ÷ 2

So, the total electron pairs = 8÷2=4

Determine The Central Atom

Because there is only two elements so we don’t need to worry about finding the  central atom, so we can draw the structure of HCl as

Mark Lone Pairs On Atom

Remember, there is a total of four electron pairs.

• There is already one bond in the drawn skeleton.
• Usually, remaining non-bonded electron pairs should be started to mark on outside atoms. Since a hydrogen atom cannot keep more than two electrons in its last shell and it has already two-electron. Therefore, we don’t mark those remaining electron pairs on the hydrogen atom.
• Therefore, the remaining three electron pairs mark on chlorine atom and complete its octet. Because the rest of the electrons which are not involved in sharing to make covalent bonds are meant to complete the octet of other atoms.

Mark Charge On Atom

To calculate formal charge, use the following formula

Formal charge = valence electrons – non bonding electrons – ½ bonding electrons

For hydrogen atom, formal charge = 1-0- ½ (2) = 0

For chlorine atom, formal charge = 7-6- ½ (2) = 0

So, there is no charge on the HCl molecule. Hence, it is a stable Lewis structure.

Convert The Lone Pair Into Bond Pair To Obtain The Best Lewis Structure of HCl

Like halogens, chlorine requires one more electron to complete its octet. Similarly, hydrogen requires one electron to complete its octet as it contains a maximum two-electron in its valence shell. As a result, a single covalent bond is formed by sharing of electrons between hydrogen and chlorine.

Check The Stability Of The Structure

It can be checked by using the same formula as

Formal charge = valence electrons – non-bonding electrons – ½ bonding electrons

Element	Chlorine	Hydrogen
Formula applied	Valence electron = 7   Lone pair electrons = 6 Shared pair electrons (1 single covalent bond) = 2	Valence electrons =1   Lone pair electrons = 0 Shared pair electron (1 single covalent bond) =2
Formal charge	(7-6- 2/2) = 0	(1-0-2/2) =0

Since the overall formal charge is zero so this structure is most reliable, appropriate, and stable in nature.

Molecular Geometry And Shape Of Molecule

Molecular geometry is the electronic structural representation of molecules. The HCl molecular geometry is the diagram that shows the number of unpaired electron and bond pairs in a specific geometric manner. The geometry of the HCl molecule can then be predicted by using Valence Shell Electron Pair Repulsion Theory (VSEPR) and molecular hybridization theory.

According to VSEPR theory, the molecule will get linear or tetrahedral geometry because the centre atom, chlorine has one H-Cl bond. The bond angle is 180 degrees and the molecule has a linear or tetrahedral shape because it has one hydrogen atom at one corner and three lone pairs of electrons at the three corners of the tetrahedron.

Determination Of Geometry By AXN Notation

The following is the AXN nomenclature for the HCl molecule:

The central chlorine atom can be represented as  A

The bond pairs can be denoted by X

The lone pair on the central chlorine atom can be denoted by the letter N

Notation for HCl molecule is AX1N3.

Polarity Of HCl Molecule

We must add bond polarities to compute the strength of the HCl bond. The electronegative potential of chlorine is higher than that of hydrogen. A more electronegative atom pulls the electron bond pair more towards itself. As a result, it acquires a slightly negative charge and becomes a negative pole, and hydrogen acquires a slightly positive charge and becomes a positive pole.

Two poles ( positive and negative) are generated across a molecule in this way. This makes a molecule polar in nature.

The dipole moment of HCl is 1.03 D.

Factors Affecting The Polarity Of HCl

• Relative Electronegativities Of Participating Atoms

The more the difference in electronegativity of the elements, the more the bond polar.

For example, a higher electronegative atom takes more control over the shared pair of electrons creating partial positive and partial negative charges which result in dipoles causing polarity.

Consider the difference in E.N in HF is 4-2.1 = 1.9

While the difference in E.N in HCl is 3-2.1= 0.9 so, HF is more polar than HCl due to a greater E.N difference.

• Symmetry Of The Molecule

In general, the more the symmetry, the lesser will be the polarity.

For example, if the molecule has symmetry around the central atom, the bond dipole moment cancels out and the molecule will therefore be non-polar.

• Total Number Of Atoms
• Total Number Of Identical Atoms Around The Central Atom
• Number Of Lone Pairs Of Electron
• Overall Shape Of Molecule

Hybridization of HCl

HCl has no hybridization, because HCl being a linear diatomic molecule, has an H atom and a Cl atom bonded covalently. So there is no need for any extra stability.

Molecular Orbital Diagram Of HCl

In simple words, the molecular orbital theory is the formation of molecular orbital by the combination of atomic orbitals of the atoms in the molecule.

This theory helps us to know the arrangement of electrons in the orbital and also the bond order.

The molecular orbital diagram can be explained as;

Physical Characteristics

• HCl is uncoloured gas and has a pungent aroma.
• Soluble in water.
• Liquefies at 189K to form colourless liquid and freezes at 159K to form a white solid.
• Its melting point is -62.25°C.
• The boiling point is 108.58°C.
• The molecular mass is 36.458 g/mol.
• HCl_aq conducts electricity.
• pH: concentrated HCl has a pH level of 0. However, HCl found in the stomach has a pH of 1 to 2.
• Corrosive in nature
• Do not support the combustion process
• It does not catch fire so it is not combustible
• Acidic in nature so turns blue litmus red

Chemical Characteristics

• Ionization: HCl is a strong acid, it means that is completely ionised into ions H⁺ _(aq) and Cl^–_(aq) when dissolved in water.
• Reactivity: It is a highly reactive acid and reacts with alkalies, water, oxidizing agents, metals, organic materials
• Corrosivity: extremely corrosive in the presence of aluminium, copper and stainless steel, severe corrosive effect on brass and bronze
• Non-corrosive: in the presence of glass
• Monoprotic: it releases one proton

Uses Of Hydrochloric Acid

• Purification Of Table Salts And Ph Control

This acid purifies table salts. It is also useful in the regulation of acidity of solutions and useful to control the pH of pharmaceutical products, water and foods.

• For The Production Of Oil

Hydrochloric acid is put into the rock where it creates large pore structures which has significant assistance in oil production.

• Cleaning Agent

Because of the highly corrosive nature of this acid, it can be used as a cleaning agent and as a disinfectant. It is used to remove stains or rust from metals like copper and iron. It is used to neutralize swimming pools if the pH level is high.

• In Textile Industry

It is used for bleaching clothes and processing in the leather and tanning industry.

• Pickling Of Steel

It is a process in which dilute HCl is used to remove rust or iron oxide layer from the steel or iron before its processing into wire production, sheets and tin mill products.

• Production Of Organic Compounds

HCl is useful in the production of organic compounds like vinyl chloride, dichloromethane etc.

• Production Of Inorganic Compounds

HCl is useful in the production of compounds that are useful as water treatment chemicals.

• Gastric Acids

Hydrochloric acid is an essential component of gastric juice, which supports digestion.

• Hydrochloric Acid Uses In Daily Life

Hydrochloric acid is the solution formed by mixing the hydrogen chloride gas in water. Some main industrial uses are as follows:

1. Production of glucose and corn sugar from starch
2. Refining of cane sugar
3. Making glue and gelatin
4. Making synthetic rubber and plastics
5. Manufacturing of aqua regia to dissolve noble metals such as gold and platinum

Conclusion

It is concluded that HCl acid is a strong colourless inorganic acid with a pungent and irritating aroma whose physical properties depend on the concentration and molarity of the acid. It has a wide range of chemical characteristics including the displacement of metal with the evolution of hydrogen gas. It ionizes completely in water giving its ions H⁺ and Cl^– so that it conducts electricity in the liquid state. It is useful in a variety of ways including as a disinfectant, and synthesis of rubber and other chemical compounds.

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