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halogenoalkanes Flashcards

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1
Q

what’s the definition of base?

A

proton acceptor

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2
Q

what is the definition of electronegativity?

A

a measure of the power of an atom to attract the shared pair of atoms in a covalent bond

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3
Q

what is the definition of hydrolysis?

A

the splitting of a molecule by a reaction with water

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4
Q

what is the definition of nucleophile?

A

electron pair of donor e.g. :OH^- :NH3 :CN^-

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5
Q
A
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6
Q

What is the electron distribution in a covalent bond between elements with different electronegativities?

A

The electron distribution will be unsymmetrical

This occurs because the positive nucleus attracts negatively charged electrons towards itself.

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7
Q

What phenomenon causes the unsymmetrical electron distribution in a covalent bond?

A

The positive nucleus’s ability to attract negatively charged electrons

This attraction occurs in the outer shells of the atoms involved in the bond.

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8
Q

What scale is used to assign a value of electronegativity for each atom?

A

The Pauling scale

The Pauling scale quantifies the tendency of an atom to attract electrons in a covalent bond.

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9
Q

What determines electronegativity?

A
  1. Nuclear charge
  2. Distance between nucleus and outer electron shells (atomic radius)
  3. Shielding (screening) by inner electron shells

These factors influence the attraction between the nucleus and bonding pair of electrons.

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10
Q

How does nuclear charge affect electronegativity?

A

The more protons, the stronger the attraction from the nucleus to the bonding pair of electrons

A higher nuclear charge increases the electronegativity.

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11
Q

How does atomic radius influence electronegativity?

A

The closer the bonding electrons to the nucleus, the stronger the attraction from the nucleus to the bonding pair of electrons

A smaller atomic radius generally leads to higher electronegativity.

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12
Q

What role does shielding play in electronegativity?

A

The less shells of electrons mean repelling the bonding electrons, the stronger the attraction from the nucleus to the bonding pair of electrons

Shielding effects can reduce the effective nuclear charge felt by outer electrons.

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13
Q

What happens to electronegativity down a group?

A

Electronegativity decreases

This is due to an increase in atomic radius and the number of energy levels.

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14
Q

Why does electronegativity decrease down a group?

A

• Number of energy levels increases
• More shielding
• Atomic radius increases
• Increase in nuclear charge is negligible
• Less attraction between nucleus and bonding electrons

Increased shielding and distance reduce the nucleus’s ability to attract bonding electrons.

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15
Q

What happens to electronegativity across a period?

A

Electronegativity increases

This trend is observed due to increasing nuclear charge and decreasing atomic radius.

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16
Q

Why does electronegativity increase across a period?

A

• Nuclear charge increases
• Atomic radius decreases
• Greater attraction between nucleus and bonding electrons

As electrons are added to the same energy level, the increased positive charge in the nucleus attracts them more strongly.

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17
Q

What is bond polarity?

A

Bond polarity is the unequal sharing of electrons between atoms that are covalently bonded.

It arises from covalent bonds between atoms with different electronegativity.

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18
Q

What causes bond polarity?

A

Bond polarity arises from covalent bonds between atoms with different electronegativity.

Electronegativity is the tendency of an atom to attract electrons.

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19
Q

What is a primary halogenoalkane?

A

A halogenoalkane where a halogen is attached to a carbon that is attached to one other alkyl group.

This classification is based on the number of carbon atoms attached to the carbon bearing the halogen.

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20
Q

What defines a secondary halogenoalkane?

A

A halogenoalkane where a halogen is attached to a carbon that is attached to two other alkyl groups.

This indicates that the carbon with the halogen is more connected within the molecular structure.

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21
Q

What characterizes a tertiary halogenoalkane?

A

A halogenoalkane where a halogen is attached to a carbon that is attached to three other alkyl groups.

This structure often results in different reactivity compared to primary and secondary halogenoalkanes.

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22
Q

Halogenoalkanes can be classified as _____, secondary, or tertiary.

A

primary

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23
Q

In a primary halogenoalkane, the carbon with the halogen is attached to _____ other alkyl group(s).

A

one

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24
Q

In a secondary halogenoalkane, the carbon with the halogen is attached to _____ other alkyl group(s).

A

two

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25
In a tertiary halogenoalkane, the carbon with the halogen is attached to _____ other alkyl group(s).
three
26
What determines the different rates of substitution reactions in halogenoalkanes?
The bond energies of the carbon-halogen bonds
27
What type of reaction do halogenoalkanes undergo?
Substitution reactions
28
Fill in the blank: The reactivity of halogenoalkanes is influenced by the _______.
[bond energies]
29
What is formed when halogenoalkanes react with aqueous silver nitrate solution?
A precipitate is formed ## Footnote The precipitate indicates the presence of halides in the halogenoalkanes.
30
How can the rate of formation of precipitates be used in chemistry?
To determine the reactivity of the halogenoalkanes ## Footnote Faster formation indicates higher reactivity.
31
What color precipitate is formed from silver chloride?
White ## Footnote Silver chloride is produced from chlorides in halogenoalkanes.
32
What color precipitate is formed from silver bromide?
Cream ## Footnote Silver bromide is produced from bromides in halogenoalkanes.
33
What color precipitate is formed from silver iodide?
Pale yellow ## Footnote Silver iodide is produced from iodides in halogenoalkanes.
34
Which halogenoalkane undergoes the fastest nucleophilic substitution reaction?
Iodoalkanes ## Footnote The formation of pale yellow silver iodide is the fastest.
35
Which halogenoalkane undergoes the slowest nucleophilic substitution reaction?
Fluoroalkanes ## Footnote The formation of silver fluoride is the slowest.
36
What confirms that fluoroalkanes are the least reactive halogenoalkanes?
The slow formation of silver fluoride ## Footnote Reactivity is determined by the rate of nucleophilic substitution.
37
What confirms that iodoalkanes are the most reactive halogenoalkanes?
The fast formation of silver iodide ## Footnote Reactivity is determined by the rate of nucleophilic substitution.
38
list the reactivity level of the alkanes: fluoro, chloro, bromo, iodo from the least to most reactive
1. fluoro 2. chloro 3. bromo 4. iodo
39
What can be used to measure the rate of hydrolysis of halogenoalkanes?
Acidified silver nitrate ## Footnote Acidified silver nitrate reacts with halogenoalkanes to form precipitates.
40
What is the temperature of the water bath used in the hydrolysis experiment?
50 °C ## Footnote The water bath maintains a consistent temperature for the reaction.
41
How many test tubes are set up for the hydrolysis experiment?
Three test tubes ## Footnote Each test tube contains a different halogenoalkane for comparison.
42
What three types of halogenoalkanes are used in the experiment?
* Chloroalkane * Bromoalkane * Iodoalkane ## Footnote These halogenoalkanes are tested to observe differences in hydrolysis rates.
43
What is the observable result of the hydrolysis reaction for chloroalkane?
White precipitate ## Footnote The formation of a white precipitate indicates the presence of chloride ions.
44
What color precipitate forms from bromoalkane during hydrolysis?
Cream precipitate ## Footnote This precipitate indicates the formation of bromide ions.
45
What color precipitate forms from iodoalkane during hydrolysis?
Yellow precipitate ## Footnote The yellow precipitate indicates the presence of iodide ions.
46
Which halogenoalkane forms a precipitate the fastest?
Iodoalkane ## Footnote The C-I bond has the lowest bond enthalpy, making it easier to break.
47
Which halogenoalkane forms a precipitate the slowest?
Chloroalkane ## Footnote The C-Cl bond has the highest bond enthalpy, making it harder to break.
48
Why does the iodoalkane react faster than the chloroalkane?
Because the C-I bond has the lowest bond enthalpy ## Footnote Lower bond enthalpy means it requires less energy to break the bond.
49
Fill in the blank: The _______ will form the slowest precipitate.
Chloroalkane ## Footnote This is due to the higher bond enthalpy of the C-Cl bond.
50
What is a nucleophile?
An electron-rich species that can donate a pair of electrons. ## Footnote 'Nucleophile' means 'nucleus/positive charge loving' as nucleophiles are attracted to positively charged species.
51
What does the term 'nucleophilic' refer to?
Reactions that involve a nucleophile.
52
True or False: All species can behave as nucleophiles.
False.
53
Fill in the blank: Nucleophiles are attracted to _______ charged species.
positively
54
What makes some nucleophiles better than others?
Various factors such as electron density and sterics.
55
What is a nucleophilic substitution reaction?
A nucleophilic substitution reaction is one in which a nucleophile attacks a carbon atom which carries a partial positive charge. ## Footnote Nucleophiles are species that donate an electron pair to form a chemical bond.
56
What happens to an atom with a partial negative charge during a nucleophilic substitution reaction?
An atom that has a partial negative charge is replaced by the nucleophile. ## Footnote This process involves the breaking of a bond between the carbon and the atom being replaced.
57
Why do halogenoalkanes undergo nucleophilic substitution reactions?
Halogenoalkanes undergo nucleophilic substitution reactions due to the polar C-X bond (where X is a halogen). ## Footnote The polarity arises from large differences in electronegativity between the carbon and halogen atom.
58
What role does electronegativity play in nucleophilic substitution reactions involving halogenoalkanes?
Electronegativity causes a polar C-X bond, which facilitates the nucleophilic substitution reaction. ## Footnote The more electronegative halogen creates a partial negative charge, making the carbon atom more susceptible to nucleophilic attack.
59
What is the definition of an Acid?
Proton donator ## Footnote Acids are substances that can donate a proton (H+) in a chemical reaction.
60
What is an Alkali?
Soluble base ## Footnote Alkalis dissolve in water to produce hydroxide ions (OH-).
61
What do nucleophiles have that allows them to form dative bonds?
Lone pairs of electrons ## Footnote Nucleophiles are electron-rich species that can donate electron pairs.
62
What role does warm, aqueous sodium hydroxide play in reactions?
Acts as a nucleophile ## Footnote Sodium hydroxide can donate electrons to form bonds with electrophiles.
63
What type of reactions occur with halogenoalkanes?
Nucleophilic substitution reactions ## Footnote These reactions involve the replacement of a leaving group by a nucleophile.
64
What product is formed when nucleophilic substitution reactions occur with halogenoalkanes?
Alcohol ## Footnote The nucleophile replaces the halogen atom to form an alcohol.
65
How can changing the conditions of a reaction affect the products?
It can change the type of reaction from substitution to elimination ## Footnote Conditions such as temperature and solvent can influence the reaction pathway.
66
Under what conditions will OH act as a base?
In an elimination reaction ## Footnote This occurs when conditions favor the removal of H+.
67
What are the conditions for an elimination reaction?
* Heat * Ethanol as a solvent (no water present) * Concentrated potassium hydroxide ## Footnote These conditions promote the elimination of H+ from the halogenoalkane.
68
What does an elimination reaction involve?
An organic molecule loses a small molecule ## Footnote In the case of halogenoalkanes, this small molecule is typically a hydrogen halide.
69
What small molecule is lost in the elimination reaction of halogenoalkanes?
Hydrogen halide (e.g., HCl) ## Footnote The elimination process results in the formation of an alkene.
70
What happens when bromoethane reacts with ethanolic sodium hydroxide when heated?
Forms ethene ## Footnote The reaction leads to the breaking of the C-X bond and the formation of an alkene.
71
for substitution reactions what type of conditions happen and what does the hydroxide ion acts as?
- low temperature - dilute hydroxide - water as solvent - hydroxide ions acts as nucleophile
72
for elimination reactions what type of conditions happen and what does the hydroxide ion acts as?
- high temperature - concentrated hydroxide - ethanol as solvent - hydroxide ions acts as base

organic chemistry (4 decks)

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