Simple molecules and covalent bonds
Introduced| English | Meaning |
|---|---|
| covalent bond/ˈkəʊvələnt bɒnd/ | A chemical bond involving a shared pair of electrons attracted to the nuclei of bonded atoms. |
| molecules/ˈmɒlɪkjuːlz/ | Groups of atoms joined by covalent bonds that can exist as discrete particles. |
| simple molecular/ˈsɪmpl məˈlekjʊlə/ | simple molecular |
Sharing, not giving
- Two non-metals can't both grab electrons — so instead they share them.
- Shared pairs of electrons form covalent bonds 共价键, holding atoms together in molecules 分子.
A covalent bond is:
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Covalent bonding shares electrons.
In a covalent bond, atoms ______ a pair of electrons.
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Sharing lets both atoms fill their outer shells.
Covalent bonds
- A covalent bond is a shared pair of electrons between two atoms.
- Sharing lets both atoms reach a full outer shell.
A model of a water molecule: atoms share electrons in covalent bonds
Covalent bonding (sharing)
Step through it: two non-metal atoms overlap and share a pair of electrons — counting for both — so each reaches a full outer shell. That shared pair is the covalent bond; O₂ shares two pairs (a double bond).
Which is a simple molecule?
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CO₂ is a small covalent molecule.
Match each idea about simple molecules.
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Strong covalent bonds hold atoms inside a molecule, but only weak forces act between molecules.
Simple molecules
- Simple molecular 简单分子 substances are small molecules (e.g. H₂O, CO₂, O₂).
- The bonds inside each molecule are strong, but the forces between molecules are weak.
Why a molecule has its shape
Shared electron pairs repel one another and spread out as far apart as they can. Four bonding pairs and no lone pairs gives a tetrahedral shape, like methane (CH4).
Simple molecular substances have low melting points because:
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Only the weak intermolecular forces need breaking.
Simple molecular substances do not conduct electricity because they have:
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No charged particles are free to move.
Their properties
- Low melting and boiling points — only the weak forces between molecules need breaking.
- They don't conduct electricity (no free electrons or ions).
It's the weak forces between molecules that melt easily — not the bonds. The covalent bonds inside a molecule are strong; melting only separates the molecules, breaking the weak forces between them. That's why simple molecules melt at low temperatures.
You've got it
- a covalent bond is a shared pair of electrons (lets atoms fill their outer shells)
- simple molecules have strong internal bonds but weak forces between molecules
- so they have low melting points and don't conduct electricity
Write from 2 shared pairs
- An oxygen molecule has a double bond between the two oxygen atoms.
- Each shared pair is one covalent bond.
How many shared pairs are in that double bond?
Each covalent bond is one shared pair.
How many electron pairs are shared in an oxygen double bond?
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A double bond is two shared pairs.