Alkanes
Introduced| English | Meaning |
|---|---|
| saturated/ˈsætʃəreɪtɪd/ | Describing a solution unable to dissolve more solute under stated conditions, or an organic molecule with no carbon-carbon double or triple bonds. |
| alkanes/ˈælkeɪnz/ | The saturated, open-chain hydrocarbons studied here, with only single carbon–carbon bonds and general formula CₙH₂ₙ₊₂. |
| single bonds/ˈsɪŋɡl bɒndz/ | single bonds |
| substitution/ˌsʌbstɪˈtjuːʃn/ | A reaction in which an atom or group in a molecule is replaced by another atom or group. |
The saturated 饱和 hydrocarbons
- The simplest family of organic compounds is the alkanes 烷烃 — the main components of fuels.
- They are saturated: every carbon bond is single.
Alkanes are described as saturated because they have:
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Saturated = all single bonds.
The general formula of the alkanes is:
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Alkanes follow CₙH₂ₙ₊₂.
The simplest alkane is:
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Methane has one carbon.
The alkane family
- Alkanes have the general formula CₙH₂ₙ₊₂.
- Examples: methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀).
The first three alkanes; each member of the series adds a CH2 unit
Burning an alkane
Step through combustion. With plenty of oxygen an alkane burns cleanly; starve it of oxygen and you get toxic carbon monoxide and soot instead.
Because they have only single bonds, alkanes are relatively ______.
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No spare bonds for addition reactions.
Saturated bonds
- "Saturated" means all the carbon–carbon bonds are single bonds 单键.
- There are no spare bonds, so alkanes are relatively unreactive.
Alkanes burn well, which is why they are used as fuels.
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Combustion releases lots of energy.
Reactions of alkanes
- Alkanes burn well (combustion), which is why they are used as fuels.
- They are otherwise unreactive but can react with halogens in sunlight (substitution 取代).
Saturated means single bonds only. Alkanes have no double bonds, so nothing can simply "add" to them. This makes them much less reactive than the alkenes.
You've got it
- alkanes are saturated hydrocarbons (all single bonds), formula CₙH₂ₙ₊₂
- examples: methane, ethane, propane, butane
- they burn as fuels but are otherwise fairly unreactive
Write from 8 hydrogen atoms in propane
- Propane is an alkane with 3 carbon atoms.
- The alkane general formula is CnH2n+2. Butane's 4 carbons are a different member.
How many hydrogen atoms are in one propane molecule?
For n equals 3, the alkane hydrogen count is 8.
How many hydrogens are in propane?
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2n+2 with n equal to 3 is 8.