Hydrogen reacts with chlorine to form hydrogen chloride - Edexcel - GCSE Chemistry Combined Science - Question 5 - 2016 - Paper 1

To represent the formation of hydrogen chloride (HCl), we start by considering the electronic configurations of hydrogen and chlorine.

Step 1: Identify the outer electrons

• Hydrogen (H) has 1 outer electron.
• Chlorine (Cl) has 7 outer electrons.

Step 2: Show bonding

In a covalent bond, the hydrogen atom shares its one electron with one of chlorine's seven outer electrons. The representation involves:

1. Drawing the hydrogen atom with its single electron as a dot:
   • H: •
2. Drawing chlorine as a large circle representing the nucleus with 7 electrons:
   • Cl: • • • • • • • (where dots represent chlorine's outer electrons).
3. To depict the bond formation, we denote the shared electron as a cross and indicate the shared pair between hydrogen and chlorine:
   • Hydrogen: •
   • Chlorine: • • • • • • •
   • Shared electron: •
   • Resulting in: H: • + Cl: • • • • • • • → H: •• Cl: • • • • • • (showing shared pair)

Final representation

The dot-and-cross diagram would visually depict this sharing as follows:

    H: ••
    Cl: • • • • • • •

This shows only the outer electrons, with the shared pair indicating a covalent bond.