Electron Sharing Reactions

플레이하며 배우기

이 문제들을 풀어 에너지를 얻은 뒤 낚시하고 탐험하세요. 계정이 필요 없어요.

교육자를 위해: Electron Sharing Reactions(Chemistry, HL)을(를) 위한 바로 쓸 수 있는 수업 슬라이드, 복습 노트 — 수업에 사용하거나, 학습자들이 실시간 게임으로 즐기는 인터랙티브 클래스 활동으로 진행하세요.

수업 노트

Radicals

A radical is a chemical species that has an unpaired electron.
Radicals can be atomic (single atom with an unpaired electron), polyatomic/molecular (group of atoms with no overall charge and an unpaired electron), anionic (negatively charged with an unpaired electron), or cationic (positively charged with an unpaired electron).
The presence of an unpaired electron is the sole requirement for a species to be a radical; charge is independent of radical character.
Radicals are indicated by a dot (•) in their formula, placed on the atom with the unpaired electron.
Examples include Cl•, Br•, CH3•, OH•, and NO•.
Radicals are highly reactive because the unpaired electron gives them high enthalpy.
To lower their enthalpy, radicals react quickly by stealing an electron from another species or combining with another radical to form a covalent bond.
Due to their high reactivity, radicals are usually short-lived.

Homolytic Fission

Homolytic fission is the breaking of a covalent bond so that each atom takes one electron from the bond, forming two radicals.
In mechanisms, a single-headed curly arrow (fish-hook arrow) shows the movement of a single electron.
The arrows start from an electron-rich region (e.g., the middle of the covalent bond) and finish at the atom where the electron goes.
Homolytic fission of halogens is the initiation step in a chain reaction.
Bond breaking is endothermic, so energy is required; the amount depends on the bond strength.
Thermolytic fission uses heat for weaker bonds: X–X → 2X•.
Photolytic fission uses high-energy UV light for stronger bonds such as halogen bonds: X–X → 2X•.

Stability and Reactivity of Alkanes

Alkanes are relatively unreactive due to the strength of C–C and C–H bonds and their non-polar nature.
The C–C and C–H bonds are strong and require a lot of energy to break, decreasing reactivity.
Carbon and hydrogen have similar electronegativities (difference of only 0.4), so electrons are shared almost equally, making alkanes nonpolar.
Alkanes have no partial positive or negative charges (δ+ and δ–), so they do not attract nucleophiles or electrophiles.
Alkanes mainly undergo combustion and free-radical substitution.

Free-Radical Substitution of Alkanes

Alkanes undergo free-radical substitution where a hydrogen atom is replaced by a halogen (chlorine or bromine).
Ultraviolet light is required to provide the energy to break the halogen bond.
The reaction proceeds in three steps: initiation, propagation, and termination.
The reaction is not suitable for preparing specific halogenoalkanes because a mixture of products is formed.
If excess halogen is present, all hydrogens can eventually be substituted, e.g., forming hexachloroethane (C2Cl6).

Initiation Step

In the initiation step, the halogen bond (Cl–Cl or Br–Br) is broken by UV energy.
The bond breaks by homolytic fission, producing two halogen radicals.
Example: Cl–Cl → 2Cl• (with UV light).

Propagation Steps

In propagation, a halogen radical attacks an alkane, breaking a C–H bond homolytically to form an alkyl radical and a hydrogen halide.
Example: CH4 + Cl• → •CH3 + HCl.
The alkyl radical then reacts with another halogen molecule to form a halogenoalkane and regenerate a halogen radical.
Example: •CH3 + Cl2 → CH3Cl + Cl•.
The regenerated halogen radical can repeat the cycle.
For ethane: CH3CH3 + Cl• → •CH2CH3 + HCl, then •CH2CH3 + Cl2 → CH3CH2Cl + Cl•.
Further substitution can occur: CH3CH2Cl + Cl• → •CH2CH2Cl + HCl, then •CH2CH2Cl + Cl2 → CH2ClCH2Cl + Cl•.
Common mistake: propagation does not produce a hydrogen radical (H•); for example, CH3CH3 + Cl• → CH3CH2Cl + H• does not happen.

Termination Steps

Termination occurs when two free radicals react together to form a single unreactive molecule, stopping the chain.
Multiple products are possible depending on which radicals combine.
Examples: CH3CH2• + Cl• → CH3CH2Cl (chloroethane).
CH3CH2• + •CH2CH3 → CH3CH2CH2CH3 (butane).
Cl• + Cl• → Cl2 (chlorine molecule).

Key Equations and Exam Tips

Initiation: Cl2 → 2Cl• (UV light).
Propagation (example with methane): CH4 + Cl• → •CH3 + HCl; •CH3 + Cl2 → CH3Cl + Cl•.
Termination (example): •CH3 + Cl• → CH3Cl; •CH3 + •CH3 → C2H6; Cl• + Cl• → Cl2.
Practice writing these equations, especially propagation steps, as they are frequently tested.
Remember that UV light is essential for the initiation step and that the reaction produces a mixture of products.

슬라이드

Step through every slide for this topic — plus flashcards and revision notes — with a free account.

가입 — 무료 로그인

연습 문제

무료 미리 보기 — 63개 중 8개 문제. 가입하면 전부 볼 수 있어요.

1.Which of these organic compounds would undergo free radical substitution? I. ethane II. fluoroethane III. ethene
Easy
- AI only
- BIII only
- CI and II only
- DI, II and III
2.Which equation represents a correct propagation step in the free radical substitution reaction between ethane and chlorine?
Medium
- AC2H6 + Cl• → C2H5Cl + H•
- BC2H5• + Cl2 → C2H5Cl + Cl•
- CC2H6 + H• → C2H5• + HCl
- DC2H5• + Cl• → C2H5Cl
3.Ultraviolet light initiates the following reaction: alkane + chlorine → chloroalkane + hydrogen chloride. What happens to chlorine in this photochemical reaction?
Easy
- Aheterolytic fission to give an electrophile
- Bhomolytic fission to give an electrophile
- Cheterolytic fission to give a positive and negative ion
- Dhomolytic fission to give free radicals
4.In the presence of ultraviolet light, ethane and chlorine react to give a mixture of products. Which compound could be present in the mixture of products?
Medium
- ACHCl3
- BCH3CH2CH2Cl
- CCH3CH2CH2CH3
- DCH3CH2CH2CH2CH3
5.Which statements about the chlorine free radical are correct? (select all that apply)
Medium
- AIt has 17 electrons.
- BIt is an uncharged species.
- CIt is formed by homolytic fission.
- DIt has a lone pair of electrons.
- EIt is a cation.
6.Which of the following organic compounds can NOT be formed during the free radical substitution reaction of ethane with chlorine?
Medium
- A1,2-dichloroethane (CH2Cl–CH2Cl)
- BChloroethane (C2H5Cl)
- CButane (C4H10)
- D1,1-dichloroethane (CH3–CHCl2)
7.Ethane reacts with bromine in the presence of ultraviolet light to form dibromoethane and hydrogen bromide. The reaction proceeds via free radical substitution involving initiation, propagation and termination steps. What is the minimum number of free radical mechanism steps to produce dibromoethane?
Hard
- A5
- B6
- C7
- D8
8.Ethane reacts with chlorine in the presence of ultraviolet light to form trichloroethane and hydrogen chloride. The reaction proceeds via free radical substitution involving initiation, propagation and termination steps. Which of the following is a valid propagation step in the mechanism for the formation of trichloroethane?
Hard
- AC2H6 + Cl• → C2H6• + HCl
- BC2H3Cl2 + Cl• → C2H3Cl3 + H•
- CC2H5• + Cl2 → C2H5Cl + Cl•
- DC2H4Cl• + Cl2 → C2H4Cl2 + Cl•

더 많은 문제

9.Ethane reacts with bromine in the presence of ultraviolet light to form tribromoethane and hydrogen bromide. The reaction proceeds via free radical substitution involving initiation, propagation and termination steps. Which equation represents a possible termination step in this reaction?
Hard
- A2C2H4• → C4H8
- BC2H4Br• + C2H5• → C4H9Br
- CC2H4• + C2H3Br• → C4H7Br
- DC2H3Br2• + C2H3Br2• → C4H6Br4
10.A radical is a chemical species that has an unpaired electron.
Easy
True or false?
11.Homolytic fission of a covalent bond produces two ions.
Easy
True or false?
12.Alkanes are highly reactive due to the polarity of the C–H bond.
Medium
True or false?
13.Match the type of radical with its description.
Medium
- Atomic radical
- Polyatomic radical
- Anionic radical
- Cationic radical
- A single atom with an unpaired electron
- A group of atoms bonded together with no overall charge, containing an unpaired electron
- An atom or molecule that gains one electron to become an anion AND has one atom with an unpaired electron
- An atom or molecule that loses one electron to become a cation AND has one atom with an unpaired electron
14.Arrange the steps of the free radical substitution mechanism in the correct order.
Medium
- Termination
- Initiation
- Propagation
15.What is the type of bond fission involved in the initiation step?
Medium
- AHomolytic fission
- BHeterolytic fission
- CNucleophilic substitution
- DElectrophilic addition
16.Which of the following is NOT a radical?
Medium
- ACl•
- B•CH3
- CNO•
- DNH4+
17.Which of the following are true about radicals? (select all that apply)
Medium
- AThey are highly reactive.
- BThey have an unpaired electron.
- CThey are always positively charged.
- DThey are usually short-lived.
- EThey can be formed by homolytic fission.
18.The radical dot (•) in a formula indicates the presence of an unpaired electron.
Easy
True or false?
19.Which of the following species contain an unpaired electron? (select all that apply)
Medium
- ACl•
- BCl⁻
- CCH₃•
- DH₂
- EOH•
20.Which of the following statements about homolytic fission are correct? (select all that apply)
Medium
- AEach atom takes one electron from the covalent bond
- BIt produces two radicals
- CIt produces a cation and an anion
- DIt requires energy because bond breaking is endothermic
- EIt is shown using double-headed curly arrows
21.Which of the following are termination steps in the free-radical substitution of ethane with chlorine? (select all that apply)
Medium
- ACl• + Cl• → Cl₂
- BCH₃CH₂• + Cl• → CH₃CH₂Cl
- CCH₃CH₂• + Cl₂ → CH₃CH₂Cl + Cl•
- DCH₃CH₂• + CH₃CH₂• → CH₃CH₂CH₂CH₃
- ECH₃CH₃ + Cl• → CH₃CH₂• + HCl
22.Which of the following statements about the initiation step in the reaction between ethane and chlorine are correct? (select all that apply)
Medium
- AUV light provides the energy to break the Cl–Cl bond
- BThe Cl–Cl bond breaks homolytically
- CTwo chlorine radicals are formed
- DA hydrogen radical is formed
- EThe C–H bond in ethane is broken in this step
23.Match each radical with its correct description.
Medium
- Atomic radical
- Polyatomic radical
- Anionic radical
- Cationic radical
- A single atom with an unpaired electron
- A group of bonded atoms with no overall charge and an unpaired electron
- An atom or molecule that gains one electron to become an anion and has an unpaired electron
- An atom or molecule that loses one electron to become a cation and has an unpaired electron
24.Match each step of the free-radical substitution mechanism with its correct description.
Medium
- Initiation
- Propagation
- Termination
- UV light breaks the halogen bond homolytically to form two radicals
- A radical reacts with a molecule to form a new radical and a new molecule, regenerating the radical chain
- Two radicals combine to form a single unreactive molecule, stopping the chain
25.Place the steps of the free-radical substitution mechanism for the reaction of ethane with chlorine in the correct order.
Medium
- Cl₂ undergoes homolytic fission under UV light to form two Cl• radicals
- A Cl• radical abstracts a hydrogen atom from ethane, forming HCl and an ethyl radical
- The ethyl radical reacts with Cl₂ to form chloroethane and regenerate a Cl• radical
- Two radicals combine to form a stable molecule, terminating the chain
26.Arrange the following steps in the correct sequence for the formation of 1,2-dichloroethane from ethane and chlorine.
Medium
- Initiation: Cl₂ → 2Cl•
- Propagation 1: CH₃CH₃ + Cl• → CH₃CH₂• + HCl
- Propagation 2: CH₃CH₂• + Cl₂ → CH₃CH₂Cl + Cl•
- Propagation 3: CH₃CH₂Cl + Cl• → CH₃CHCl• + HCl
- Propagation 4: CH₃CHCl• + Cl₂ → CH₂ClCH₂Cl + Cl•
27.Which of the following is the correct equation for a propagation step in the reaction between ethane and chlorine?
Medium
- ACH₃CH₃ + Cl• → CH₃CH₂• + HCl
- BCH₃CH₂• + Cl₂ → CH₃CH₂Cl + Cl•
- CCl₂ → 2Cl•
- DCH₃CH₂• + Cl• → CH₃CH₂Cl
28.Which of the following is NOT a termination step in the free-radical substitution of ethane with chlorine?
Medium
- ACl• + Cl• → Cl₂
- BCH₃CH₂• + Cl• → CH₃CH₂Cl
- CCH₃CH₂• + CH₃CH₂• → CH₃CH₂CH₂CH₃
- DCH₃CH₂• + Cl₂ → CH₃CH₂Cl + Cl•
29.Homolytic fission of a covalent bond produces two radicals.
Easy
True or false?
30.Alkanes are highly reactive due to the polarity of their C–H bonds.
Easy
True or false?
31.A hydrocarbon with the formula C5H12 is reacted with an excess of bromine in the presence of UV light. Which of the following products is most likely to be formed?
Medium
- AC5H11Br
- BC5H10Br2
- CC5H12Br
- DC5H11Br2
32.The free radical substitution of ethane with chlorine produces a mixture of products. Which of the following statements explains why a mixture is formed?
Medium
- AThe chlorine radical can react with ethane or with chloroethane.
- BThe reaction only produces one product.
- CEthane can undergo addition reactions with chlorine.
- DThe termination steps only produce chloroethane.
33.In the free radical substitution of methane with chlorine, the following propagation steps occur: Step 1: CH4 + Cl• → •CH3 + HCl Step 2: •CH3 + Cl2 → CH3Cl + Cl• What is the overall equation for the reaction?
Medium
- ACH4 + Cl2 → CH3Cl + HCl
- BCH4 + 2Cl2 → CH3Cl + 2HCl
- CCH4 + Cl• → CH3Cl + H•
- DCH4 + Cl2 → CH2Cl2 + HCl
34.In the free radical substitution of ethane with chlorine, the termination step can produce butane.
Easy
True or false?
35.Which of the following is a valid propagation step in the mechanism for the formation of tribromoethane from ethane and bromine?
Hard
- AC2H5• + Br2 → C2H5Br + Br•
- BC2H4Br• + Br2 → C2H4Br2 + Br•
- CC2H3Br2• + Br2 → C2H3Br3 + Br•
- DC2H6 + Br• → C2H5• + HBr
36.A student sets up three test tubes: tube 1 contains bromine water and hexane in the dark, tube 2 contains bromine water and hexane in sunlight, and tube 3 contains bromine water only in sunlight. In which tube(s) would the orange colour of bromine disappear?
Medium
- ATube 1 only
- BTube 2 only
- CTubes 1 and 3
- DTubes 2 and 3
37.Which of the following statements about the practical conditions needed for the free-radical substitution of ethane with bromine are correct? (select all that apply)
Medium
- AUltraviolet light is required to break the Br–Br bond.
- BThe reaction proceeds rapidly in the dark at room temperature.
- CBromine radicals are formed by homolytic fission of Br2.
- DThe reaction produces a single pure organic product.
- EThe reaction can be initiated by heating because the Br–Br bond is weak.
38.In free-radical substitution, the initiation step can be brought about by either UV light or heat, depending on the strength of the bond being broken.
Easy
True or false?
39.Match each experimental observation or condition with the correct explanation for the reaction of ethane with chlorine.
Medium
- UV light is required
- A mixture of chlorinated products forms
- The reaction stops when radicals combine
- Chlorine radicals are regenerated in propagation
- It provides energy to break the Cl–Cl bond homolytically
- All hydrogen atoms can be successively substituted
- Two radicals form a single unreactive molecule
- The chain reaction can continue
40.Place the following practical steps in the correct order for carrying out and observing the free-radical substitution of ethane with chlorine.
Medium
- Mix ethane and chlorine in a test tube.
- Expose the mixture to UV light.
- Observe the formation of a mixture of chloroalkanes.
- Remove the UV light source to stop the reaction.
41.What is the name of the bond breaking process in which each atom takes one electron from the bond to form two radicals?
Easy
42.How many electrons does a chlorine free radical (Cl•) have?
Medium
43.Complete the sentence about the initiation step in the reaction between ethane and chlorine.
Easy
In the initiation step, the Cl–Cl bond undergoes ____ fission to form two ____.
44.Complete the equation for the initiation step in the reaction between bromine and ethane under UV light.
Medium
Br–Br → ____
45.What is the term for a chemical species that has an unpaired electron?
Easy
46.How many electrons are involved in the formation of a chlorine radical from Cl2?
Medium
47.How many electrons are involved in the formation of a chlorine radical from Cl₂?
Easy
48.How many free radical mechanism steps are required as a minimum to produce dichloromethane (CH₂Cl₂) from methane and chlorine?
Medium
49.Complete the equation for a propagation step in the reaction between ethane and chlorine.
Easy
CH₃CH₂• + ____ → CH₃CH₂Cl + ____
50.How many moles of chlorine molecules are required to completely convert 1 mole of methane to tetrachloromethane (CCl4) via free radical substitution?
Medium
51.Complete the sentence about the termination step in the free radical substitution of ethane with chlorine.
Medium
In the termination step, two ____ combine to form a single unreactive molecule.
52.What is the minimum number of free radical mechanism steps to produce dibromoethane?
Hard
53.Explain why alkanes are unreactive.
Hard
54.Write the equations for the two propagation steps.
Medium
55.Write an equation to show how ethane can be formed in this reaction.
Medium
56.Explain why a bromine atom can be described as an atomic radical.
Hard
57.State two conditions that are required to form a bromine radical from a bromine molecule.
Hard
58.How many electrons does a chlorine free radical (Cl•) have?
Medium
- A19 electrons
- B17 electrons
- C18 electrons
- D16 electrons
59.How many electrons are involved in the formation of a chlorine radical from Cl2?
Medium
- A2 electrons
- B1 electrons
- C4 electrons
- D3 electrons
60.How many electrons are involved in the formation of a chlorine radical from Cl₂?
Easy
- A3 electrons
- B4 electrons
- C1 electrons
- D2 electrons
61.How many free radical mechanism steps are required as a minimum to produce dichloromethane (CH₂Cl₂) from methane and chlorine?
Medium
- A8 steps
- B7 steps
- C9 steps
- D6 steps
62.How many moles of chlorine molecules are required to completely convert 1 mole of methane to tetrachloromethane (CCl4) via free radical substitution?
Medium
- A5 mol
- B3 mol
- C6 mol
- D4 mol
63.What is the minimum number of free radical mechanism steps to produce dibromoethane?
Hard
- A6 steps
- B5 steps
- C4 steps
- D7 steps

Unlock all 63 questions & more

무료 계정을 만들어 이 주제의 모든 문제, 슬라이드, 플래시카드, 복습 노트를 확인하세요.

가입 — 무료 로그인

기출 문제

이 주제의 기출 문제 연습이 곧 나와요.

곧 출시