Introduction to Group 7 Elements

Group 7 elements in the periodic table, also known as the halogens, are highly reactive non-metals. They are found in the second-to-last column of the periodic table and include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements share similar chemical properties and follow certain trends, which make them unique.

For Year 8 students, we will focus on the properties, reactivity, and uses of these halogens, with particular emphasis on fluorine, chlorine, bromine, and iodine.

Key Characteristics of Group 7 Elements

1. Reactivity: Group 7 elements are very reactive, with reactivity decreasing as you go down the group. Fluorine is the most reactive, while iodine and astatine are less so.
2. Physical State: Halogens exist in different states at room temperature. Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid.
3. Colour: The elements in Group 7 display distinct colours. For example, chlorine is greenish-yellow, bromine is reddish-brown, and iodine is a dark purple solid.
4. Toxicity: Halogens are toxic and can be harmful to living organisms. Proper handling and safety measures are essential when working with these elements.
5. Diatomic Nature: Halogens form molecules in pairs, such as F₂, Cl₂, Br₂, and I₂.

Reactions of Group 7 Elements

Halogens readily react with metals to form ionic compounds called salts. For instance, sodium and chlorine react to produce sodium chloride (table salt). They can also react with hydrogen to form hydrogen halides, like hydrogen chloride (HCl), which dissolves in water to form hydrochloric acid.

Exam Questions on Group 7 Elements

To assess understanding, here are 20 questions each at easy, medium, and hard levels.

Easy Level Questions

Basic Understanding of Group 7 Elements

1. What is the common name for Group 7 elements?
2. List the first four elements in Group 7.
3. What is the chemical symbol for chlorine?
4. What is the physical state of fluorine at room temperature?
5. Describe the colour of chlorine gas.
6. Which Group 7 element is a liquid at room temperature?
7. What type of molecule do halogens form?
8. What is the chemical symbol for iodine?
9. Do halogens increase or decrease in reactivity as you go down the group?
10. Name the gas produced when chlorine reacts with hydrogen.
11. Why should halogens be handled carefully?
12. Which halogen has the lowest atomic number?
13. What is formed when a halogen reacts with a metal?
14. What is the colour of iodine in its solid form?
15. Are halogens metals or non-metals?
16. Which halogen is the most reactive?
17. What is the physical state of iodine at room temperature?
18. What is formed when hydrogen reacts with chlorine?
19. Is bromine a solid, liquid, or gas at room temperature?
20. Why do halogens exist in pairs, such as Cl₂ or Br₂?

Medium Level Questions

Intermediate Knowledge and Reactions

1. Explain why Group 7 elements are called halogens.
2. Describe the appearance of bromine at room temperature.
3. How does the reactivity of iodine compare to chlorine?
4. What happens when fluorine reacts with hydrogen?
5. Why is fluorine more reactive than chlorine?
6. Write a balanced equation for the reaction of chlorine with hydrogen.
7. What are the products when sodium reacts with bromine?
8. Describe a use of chlorine in daily life.
9. What precautions should be taken when handling chlorine gas?
10. What is the appearance of iodine vapour when heated?
11. Explain why reactivity decreases down Group 7.
12. What is produced when chlorine dissolves in water?
13. What colour is fluorine gas?
14. What are the uses of iodine in medicine?
15. Why are halogens not found as free elements in nature?
16. Describe how halogens react with alkali metals like sodium.
17. What safety measure is used to store bromine?
18. What kind of bonding occurs between halogens and metals?
19. Why is chlorine added to drinking water?
20. How does the density of halogens change down the group?

Hard Level Questions

Advanced Concepts and Applications

1. Explain the trend in atomic radius as you go down Group 7.
2. Discuss the trend in electronegativity in Group 7 elements.
3. Explain why fluorine is the most reactive halogen.
4. Compare the reaction of chlorine and bromine with iron.
5. Why do halogens readily form salts with alkali metals?
6. Write the electron configuration for chlorine and bromine.
7. Explain why fluorine has a higher electronegativity than iodine.
8. Describe why halogens are poor conductors of electricity.
9. What happens to the boiling point as you go down Group 7?
10. Discuss why fluorine is difficult to store safely.
11. Describe the bonding in hydrogen halides.
12. Explain why halogens are diatomic in nature.
13. Discuss the acidic nature of hydrogen halides in water.
14. What impact do halogens have on the environment?
15. Explain why astatine is rarely found in nature.
16. Describe the trend in melting points down Group 7.
17. How does the intermolecular force change as you go down Group 7?
18. Explain why iodine is used as an antiseptic.
19. Why is fluorine highly reactive with almost all elements?
20. Describe the role of halogens in organic chemistry reactions.

Answers and Explanations

Easy Level Answers

1. Halogens – Group 7 elements are commonly known as halogens.
2. Fluorine, Chlorine, Bromine, Iodine – The first four elements in Group 7.
3. Cl – Chlorine’s chemical symbol.
4. Gas – Fluorine is a gas at room temperature.
5. Greenish-yellow – Chlorine is a greenish-yellow gas.
6. Bromine – The only Group 7 element that is a liquid at room temperature.
7. Diatomic molecules – Halogens form pairs, like F₂ and Cl₂.
8. I – The chemical symbol for iodine.
9. Decrease – Reactivity decreases as you go down the group.
10. Hydrogen chloride – This gas is formed when chlorine reacts with hydrogen.
11. They are toxic – Halogens can be harmful if inhaled or touched.
12. Fluorine – The first element in Group 7 with the lowest atomic number.
13. A salt – When a halogen reacts with a metal, a salt is formed.
14. Dark purple – Solid iodine has a dark purple colour.
15. Non-metals – Halogens are non-metals.
16. Fluorine – It is the most reactive halogen.
17. Solid – Iodine is a solid at room temperature.
18. Hydrogen chloride – Formed when hydrogen reacts with chlorine.
19. Liquid – Bromine is a liquid at room temperature.
20. To become stable – Halogens pair up as diatomic molecules to have a stable electron configuration.

Medium Level Answers

1. The term ‘halogen’ means ‘salt-former’. Halogens react with metals to form salts.
2. Bromine is a reddish-brown liquid at room temperature.
3. Iodine is less reactive than chlorine due to its larger atomic radius and lower electronegativity.
4. Fluorine reacts explosively with hydrogen due to its high reactivity.
5. Fluorine is more reactive than chlorine because it has a stronger attraction for electrons.
6. Cl₂ + H₂ → 2HCl – Chlorine reacts with hydrogen to form hydrogen chloride.
7. Sodium bromide – When sodium reacts with bromine, it forms sodium bromide (NaBr).
8. Chlorine is used as a disinfectant in swimming pools and for drinking water.
9. Chlorine gas is toxic and must be handled in a fume cupboard with protective equipment.
10. Iodine vapour is purple when iodine is heated.
11. Reactivity decreases down Group 7 due to increasing atomic radius and electron shielding.
12. Chlorine dissolves in water to produce a weak acid solution that can act as a disinfectant.
13. Pale yellow – Fluorine gas is pale yellow in colour.
14. Iodine is used as an antiseptic to disinfect wounds.
15. **Halogens are too reactive to exist freely in nature**; they are always in compounds.
16. They form ionic bonds with metals, producing salts like sodium chloride.
17. Bromine is stored in sealed glass containers to prevent its vapours from escaping.
18. Ionic bonding occurs between halogens and metals.
19. Chlorine kills bacteria in drinking water, making it safe to consume.
20. Density increases down the group as atomic mass increases.

Hard Level Answers

1. The atomic radius increases down Group 7 as more electron shells are added.
2. Electronegativity decreases down the group as the distance from the nucleus increases.
3. Fluorine is the most reactive halogen due to its high electronegativity and small atomic radius.
4. Chlorine reacts more readily with iron than bromine due to its higher reactivity.
5. Halogens form salts with alkali metals easily due to their tendency to gain one electron.
6. Chlorine: 1s² 2s² 2p⁶ 3s² 3p⁵; Bromine: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵
7. Fluorine’s high electronegativity is due to its small atomic radius and strong nuclear charge.
8. Halogens are poor conductors because they lack free-moving electrons.
9. Boiling point increases down the group as atomic mass and London dispersion forces increase.
10. Fluorine is extremely reactive and difficult to contain without special equipment.
11. Hydrogen halides form covalent bonds between hydrogen and halogens.
12. Halogens are diatomic to complete their outer electron shell.
13. Hydrogen halides form acidic solutions in water due to the release of hydrogen ions.
14. Halogens can be harmful to the environment as they contribute to pollution and ozone depletion.
15. Astatine is rare due to its radioactive nature and short half-life.
16. Melting points increase down the group due to stronger intermolecular forces.
17. Intermolecular forces increase as atomic size increases down Group 7.
18. Iodine is used as an antiseptic because it kills bacteria and other pathogens.
19. Fluorine’s high reactivity is due to its electronegativity, allowing it to bond easily.
20. Halogens are important in organic reactions, especially in the synthesis of compounds.

These questions and answers should help Year 8 students develop a solid understanding of Group 7 elements and their properties, preparing them effectively for their Key Stage 3 exams.