Science (086) — AI-generated practice question

Each hydrogen atom has 1 electron in its outermost shell and needs 2 electrons (like helium, a noble gas) to have a completely filled shell.

When two hydrogen atoms come together, each contributes 1 electron to form a shared pair — a covalent bond. This shared pair of electrons is counted by both atoms simultaneously.

Thus, each hydrogen atom effectively has 2 electrons in its outermost shell, achieving the electronic configuration of helium (a noble gas). The molecule formed is H₂.

H• + •H → H:H (shared pair)

Source: Chapter 4, "What you have learnt" — Covalent bonds are formed by the sharing of electrons between two atoms so that both can achieve a completely filled outermost shell.

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• Examiners award marks for three points: (1) what each H atom needs, (2) how sharing works, and (3) the noble gas configuration achieved.
• Always name the noble gas (helium) whose configuration H achieves — this earns the specific mark.
• The electron dot diagram (H:H) is a good addition in a 3-mark answer; it shows understanding without taking extra time.
• Do not confuse "shared pair counted by both" — this is the key idea of covalent bonding.