3.3.3 Halogenoalkanes for A-Level Chemistry (AQA)

What type of bond is present between carbon and halogen atoms in halogenoalkanes?

Polar covalent bond

The electronegative halogen pulls electron density away from carbon.

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What type of reaction occurs when a halogenoalkane reacts with a nucleophile?

Nucleophilic substitution

The nucleophile replaces the halogen atom.

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Fill in the blank:

A species that donates a lone pair of electrons to form a bond is called a _______.

nucleophile

Nucleophiles are electron-pair donors.

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True or False:

Aqueous Hydroxide ions can act as nucleophiles in substitution reactions.

True

OH^- attacks the electron-deficient carbon atom.

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What product forms when a halogenoalkane reacts with hydroxide ions?

Alcohol

The OH^- replaces the halogen atom.

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True or False:

Cyanide ions reacting with halogenoalkanes increase the carbon chain length.

True

CN^- introduces an additional carbon atom to the molecule.

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Fill in the blank:

Reaction of a halogenoalkane with ammonia forms a _______.

amine

NH₃ replaces the halogen to form an amine group.

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Why is the carbon atom in a halogenoalkane susceptible to nucleophilic attack?

Partial positive charge

The polar C–X bond leaves carbon slightly electron deficient.

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True or False:

The strength of the carbon–halogen bond affects the rate of nucleophilic substitution.

True

Weaker bonds break more easily and react faster.

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Fill in the blank:

As the carbon–halogen bond enthalpy decreases, the rate of reaction generally _______.

increases

Iodoalkanes react faster than chloroalkanes. Bromoalkanes are in the middle.

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Which halogenoalkane typically reacts fastest in nucleophilic substitution reactions?

Iodoalkane

The C–I bond is weakest among common halogenoalkanes. This is because the bond length is greater thus the nuclear attraction to the outer electrons is weaker.

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Why do iodoalkanes react faster than chloroalkanes in substitution reactions?

Weaker carbon–halogen bond

Lower bond enthalpy makes bond breaking easier.

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What type of reaction forms an alkene from a halogenoalkane by removing a hydrogen halide?

Elimination

A hydrogen atom and a halogen atom are removed from adjacent carbons.

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What type of organic product is formed during elimination of a halogenoalkane?

Alkene

The reaction creates a carbon–carbon double bond.

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Fill in the blank:

During elimination, a halogenoalkane loses hydrogen and a _______ atom.

halogen

The removed atoms combine to form HX.

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True or False:

Elimination and substitution reactions can occur simultaneously in halogenoalkane reactions.

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True

The reaction conditions determine which pathway dominates.

What reagent is commonly used to cause elimination in halogenoalkanes?

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Ethanolic Potassium hydroxide

Usually used in ethanolic solution to favour elimination. Ethanolic means dissolved in alcohol.

True or False:

Hydroxide ions can act as both nucleophiles and bases.

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True

They can attack carbon (substitution) or remove a proton (elimination).

Fill in the blank:

In elimination reactions, the ethanolic hydroxide ion acts as a _______ by removing a proton.

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base

It removes H⁺ from a neighbouring carbon atom.

What role does aqueous hydroxide play in nucleophilic substitution reactions?

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Nucleophile

It donates a lone pair to form a new bond with carbon.

True or False:

In elimination reactions, the hydroxide ion removes a hydrogen atom as H⁺.

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True

This leads to formation of a double bond between carbons.

Fill in the blank:

The elimination of HBr from 2-bromopropane forms the alkene _______.

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propene

A double bond forms between two carbon atoms.

Why can potassium hydroxide cause both substitution and elimination reactions?

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Dual role

OH^- can act either as a nucleophile or a base depending on conditions.

What structural change occurs in the organic molecule during elimination?

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Double bond formation

Removal of HX allows formation of a C=C bond.

What **molecule** in the **upper atmosphere** absorbs harmful ultraviolet radiation?

Ozone ## Footnote O₃ absorbs UV radiation and protects living organisms from damage.

In which **layer of the atmosphere** is the **ozone layer** found?

Stratosphere ## Footnote The ozone layer is located above the troposphere.

# Fill in the blank: **Ozone molecules** contain _\_\_\_\_\_\_ oxygen atoms.

three ## Footnote The chemical formula of ozone is O₃.

# True or False: **Ozone** protects life on Earth by absorbing **ultraviolet radiation**.

True ## Footnote This prevents harmful UV rays from reaching the Earth’s surface.

What **compounds** were once widely used as **refrigerants and solvents** but damage the ozone layer?

Chlorofluorocarbons ## Footnote These compounds are commonly called CFCs.

# True or False: **Ultraviolet radiation** can break the **carbon–chlorine bonds in CFCs**.

True ## Footnote This process forms chlorine radicals in the atmosphere.

# Fill in the blank: When **CFC molecules break down**, they release chlorine _\_\_\_\_\_\_.

radicals ## Footnote These radicals are highly reactive species with unpaired electrons.

What **role** do **chlorine radicals** play in ozone depletion?

Catalysts ## Footnote They speed up ozone decomposition without being consumed.

# True or False: **Chlorine radicals** are regenerated during **ozone destruction reactions**.

True ## Footnote This allows one radical to destroy many ozone molecules.

# Fill in the blank: In the reaction Cl· + O₃ → ClO· + O₂, ozone is converted into _\_\_\_\_\_\_.

oxygen ## Footnote Ozone decomposes into molecular oxygen.

Why can a single **chlorine radical** destroy many **ozone molecules**?

Catalyst regeneration ## Footnote The chlorine radical is reformed at the end of the reaction cycle. ClO· + O3 → 2O2 + Cl·

Why were **CFCs** eventually **banned in many countries**?

Scientific evidence ## Footnote Research showed they were responsible for depletion of the ozone layer.

3.3.3 Halogenoalkanes Flashcards

Predict reaction pathways by applying nucleophilic substitution and elimination mechanisms to halogenoalkanes. (36 cards)