3f. The covalent bonding in the hydrogen chloride molecule

Doc Brown's Chemistry: Chemical Bonding and structure GCSE level, IGCSE, O, IB, AS, A level US grade 9-12 level Revision Notes

Covalent bonding diagram for HYDROGEN CHLORIDE covalent molecule, molecular formula HCl

* metals \ non-metals (zig-zag line)

Pd metals Part of the modern Periodic Table

Pd = period, Gp = group

metals => non–metals
Gp1 Gp2 Gp3 Gp4 Gp5 Gp6 Gp7 Gp0
1 1H  Note that hydrogen does not readily fit into any group but is a non-metal 2He
2 3Li 4Be atomic number Chemical Symbol eg 4Be 5B 6C 7N 8O 9F 10Ne
3 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar
4 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr
5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe
6 55Cs 56Ba Transition Metals 81Tl 82Pb 83Bi 84Po 85At 86Rn
The covalent molecule hydrogen chloride from hydrogen combining with chlorine


One atom of hydrogen (1) combines with one atom of chlorine (2.8.7) to form the molecule of the compound hydrogen chloride HCl

Both hydrogen and chlorine have one electron short of a full outer shell (2 for H, 8 for Cl), so both atoms share an electron to have full outer shells.

(c) doc b and (c) doc b combine to form (c) doc b where hydrogen is electronically like helium (2) and chlorine like argon (2.8.8).

dot and cross diagram of the hydrogen chloride moleculeThe hydrogen chloride molecule is held together by the strong hydrogen–chlorine single covalent bond by sharing electrons, H–Cl (displayed formula).

Note that the two inner shells of chlorine's electrons (2.8.7) are NOT shown (see chlorine atom diagram in example 2.

Electronically, hydrogen (1) becomes like helium (2) and chlorine (2.8.7) becomes like argon (2.8.8), so the hydrogen and chlorine atoms effectively have full outer shells in forming the covalent bonds when the atoms share their outer electrons. The two inner shells of chlorine's electrons are not shown, only the outer shells of electrons are involved in the covalent bonding here.

(Lewis diagram of hydrogen chloride) simplified 'dot and cross' electronic diagram for the covalently bonded hydrogen chloride molecule.

  is the full 'dot and cross' electronic diagram for the covalent bonding in the hydrogen chloride molecule - all the electrons are shown.

The electronic dot & cross Lewis diagrams for covalent bonding in hydrogen chloride.

All the other hydrogen halides will be similar e.g. hydrogen fluoride HF, hydrogen bromide HBr and hydrogen iodide HI.

ball and stick model of hydrogen chloride

   space-filling model of hydrogen chloride


Hydrogen chloride gas is a true covalent substance consisting of small HCl molecules.

If the gas is dissolved in a hydrocarbon solvent like hexane or methylbenzene it remains as covalent HCl molecules and because there are no ions present, the solution does not conduct electricity.

However, if hydrogen chloride gas is dissolved in water, things are very different and the HCl molecules split into ions.

Hydrochloric acid is formed which consists of a solution of hydrogen ions (H+) and chloride ions (Cl).

The solution then conducts electricity and passage of a d.c. current causes electrolysis to take place forming hydrogen and chlorine.



Melting point of hydrogen chloride -114 oC

Boiling point of hydrogen chloride -85 oC

Hydrogen chloride is a very acidic choking colourless gas at room temperature.

Reminder: How to work out formula of covalent compounds without going through some demanding electronic thinking is described on the "Elements, Compounds and Mixtures" page and it is followed by a section on naming compounds.

What next?

Recommend next: The covalent bonding in the water and hydrogen sulfide molecules

Explaining the properties of small covalently bonded molecules


Sub-index for Part 3. Covalent Bonding: small molecules & properties


Index for ALL chemical bonding and structure notes


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