Chemistry - 4CH1 PearsonEdexcel

Alkenes

Gbogbo ọrọ náà

Alkenes are the reactive cousins of alkanes. A single structural difference - a carbon-carbon double bond - transforms their chemistry completely. Where alkanes are sluggish, alkenes snap up incoming atoms in addition reactions, making them the starting materials for plastics, alcohols, and countless industrial chemicals.

In this lesson you will learn the general formula for alkenes, how to draw and name them, why the double bond makes them unsaturated, and how they react with bromine. You will also discover the bromine water test, a simple way to tell an alkene from an alkane in the laboratory.

Ebumnobi

know that alkenes contain the functional group >C=C<
know the general formula for alkenes
explain why alkenes are classified as unsaturated hydrocarbons
understand how to draw the structural and displayed formulae for alkenes with up to four carbon atoms in the molecule, and name the unbranched-chain isomers knowledge of cis/trans or E/Z notation is not required
describe the reactions of alkenes with bromine to produce dibromoalkanes
describe how bromine water can be used to distinguish between an alkane and an alkene

Akọmọ Ojú-ẹkọ

Replace just one single bond between two carbon atoms with a double bond and the entire character of the molecule changes. That double bond is a region of high electron density, making alkenes far more reactive than their alkane counterparts. This reactivity is why the petrochemical industry cracks alkanes to produce alkenes, and why alkenes are the building blocks for polymers like polyethene.

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Ayẹwo Ẹkọ

Ekele diri gi maka imecha ihe karịrị na Alkenes. Ugbu a na ị na-enyochakwa isi echiche na echiche ndị dị mkpa, ọ bụ oge iji nwalee ihe ị ma. Ngwa a na-enye ụdị ajụjụ ọmụmụ dị iche iche emebere iji kwado nghọta gị wee nyere gị aka ịmata otú ị ghọtara ihe ndị a kụziri.

Ị ga-ahụ ngwakọta nke ụdị ajụjụ dị iche iche, gụnyere ajụjụ chọrọ ịhọrọ otu n’ime ọtụtụ azịza, ajụjụ chọrọ mkpirisi azịza, na ajụjụ ede ede. A na-arụpụta ajụjụ ọ bụla nke ọma iji nwalee akụkụ dị iche iche nke ihe ọmụma gị na nkà nke ịtụgharị uche.

Jiri akụkụ a nke nyocha ka ohere iji kụziere ihe ị matara banyere isiokwu ahụ ma chọpụta ebe ọ bụla ị nwere ike ịchọ ọmụmụ ihe ọzọ. Ekwela ka nsogbu ọ bụla ị na-eche ihu mee ka ị daa mba; kama, lee ha anya dị ka ohere maka ịzụlite onwe gị na imeziwanye.

What is the general formula for alkenes? A) CnH2n+2 B) CnH2n C) CnH2n-2 D) CnH2n+1OH Answer: B
Which of the following is the functional group of alkenes? A) -OH B) -COOH C) C=C D) C-C Answer: C
When bromine water is added to an alkene, the solution: A) Turns blue B) Stays orange C) Is decolourised D) Turns green Answer: C
The reaction of ethene with bromine is an example of: A) Substitution B) Decomposition C) Neutralisation D) Addition Answer: D
Why is there no alkene with only one carbon atom? A) One carbon cannot form four bonds B) A C=C double bond needs at least two carbon atoms C) Single-carbon molecules are always gases D) Methene is too unstable to exist Answer: B