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💡 Different-element partners
When atoms of different elements share electrons — hydrogen with chlorine, or hydrogen with oxygen — they build a molecule of a compound.
How does a water molecule form?
- Oxygen needs 2 electrons; each hydrogen needs 1 .
- Two hydrogen atoms each share an electron with one oxygen atom .
- This gives the water molecule, written H₂O (2 hydrogen + 1 oxygen).
In hydrogen chloride, hydrogen and chlorine each need one electron, so they share one pair and bond as H—Cl — a covalent compound.
Important Definitions
- Molecule of a compound — a molecule made of atoms of different elements, e.g. H₂O, HCl.
