The bond that shares
Show on a big screenTwo hydrogen atoms meet. Neither one gives its electron to the other.
- Carbon and four hydrogens each hold their own electrons.
- Each hydrogen shares one pair with carbon, in the overlap.
- Four shared pairs make four bonds — the formula is CH₄.
Slide in hydrogens. Watch carbon count its outer electrons.
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The rule
The two hydrogen atoms share one pair of electrons. That makes an H₂ molecule.
A bond made by a shared pair is a covalent bond.
An atom shares electrons when taking or giving costs too much. A shared pair counts into both atoms' outer shells at once. Sharing does not make charged particles by itself. Most covalent compounds are poor conductors.
A metal gives electrons to a non-metal. Carbon cannot fill its shell that way. Removing four electrons, or adding four, costs too much energy. So carbon shares.
Many covalent compounds melt and boil at low temperatures.
| The way | Who travels it | What is left behind |
|---|---|---|
| Taking and giving | A metal and a non-metal | Charged particles. The compound conducts when melted or dissolved. |
| Sharing | Non-metal atoms together | No charged particles from the sharing. |
Carbon has four outer electrons and needs four more. Four hydrogens each bring one. That makes four shared pairs.
Carbon now counts eight electrons in its outer shell. Each hydrogen counts two. Both kinds of atom have full outer shells. This is methane, CH₄. A compound of only carbon and hydrogen is a hydrocarbon.
Try the lab to finish this lesson.