Year 8 Chemistry: Group 1 Elements

Introduction to Group 1 Elements

In the periodic table, elements are grouped based on their properties. Group 1 elements, also known as alkali metals, are on the far left side of the periodic table. This group includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). These metals share similar characteristics due to their position in Group 1, such as being highly reactive and having low melting and boiling points compared to other metals.

In Year 8 science, you’ll focus on the properties and reactions of the first three elements in this group: lithium, sodium, and potassium.

Key Characteristics of Group 1 Elements

1. Reactivity: Group 1 elements are highly reactive, particularly with water and oxygen. Their reactivity increases as you move down the group from lithium to potassium.
2. Appearance: Alkali metals are shiny when freshly cut, but they quickly tarnish as they react with air.
3. Softness: These metals are softer than most, and they can often be cut with a knife.
4. Low Density: Lithium, sodium, and potassium have low densities. Lithium and sodium are less dense than water, allowing them to float.
5. Storage: Because of their high reactivity, alkali metals are stored in oil to prevent them from reacting with oxygen and moisture in the air.

Reactions of Group 1 Elements

Group 1 metals react vigorously with water to form an alkaline solution and hydrogen gas. This reaction can be quite dramatic, especially with sodium and potassium. For example:

Sodium + Water → Sodium Hydroxide + Hydrogen

The reaction releases heat, causing the hydrogen gas to sometimes ignite, especially in potassium.

Exam Questions on Group 1 Elements

To test your understanding of Group 1 elements, here are 20 questions each at easy, medium, and hard levels.

Easy Level Questions

Basic Understanding of Group 1 Elements

1. What is the common name for Group 1 elements?
2. List the first three elements in Group 1.
3. What is the chemical symbol for sodium?
4. What happens to the appearance of alkali metals when they are cut?
5. What state of matter are Group 1 elements at room temperature?
6. What happens when Group 1 metals react with water?
7. Name the gas produced when sodium reacts with water.
8. Why are Group 1 elements stored in oil?
9. Are Group 1 elements hard or soft compared to other metals?
10. Which Group 1 element has the lowest atomic number?
11. Why do Group 1 elements tarnish quickly in the air?
12. What is the product formed when lithium reacts with water?
13. Are alkali metals dense or not very dense compared to water?
14. Do Group 1 elements get more or less reactive as you go down the group?
15. Why do alkali metals float on water?
16. What type of solution is formed when an alkali metal reacts with water?
17. Name a safety precaution for handling Group 1 elements.
18. What colour flame does lithium produce when it burns?
19. How many electrons do all Group 1 elements have in their outer shell?
20. What is formed when an alkali metal reacts with oxygen?

Medium Level Questions

Intermediate Knowledge and Reactions

1. Explain why Group 1 elements are called alkali metals.
2. Describe what you would observe when lithium reacts with water.
3. How does sodium react with water compared to lithium?
4. What colour flame does potassium produce when it burns?
5. Why does reactivity increase as you move down Group 1?
6. Write a balanced equation for the reaction of potassium with water.
7. What are the products when sodium reacts with oxygen?
8. Why is it dangerous to handle Group 1 elements with bare hands?
9. How would you safely dispose of a small piece of sodium?
10. What is the appearance of freshly cut potassium?
11. Explain why potassium is more reactive than lithium.
12. What solution pH would you expect from the reaction of sodium with water?
13. What is the product when lithium reacts with chlorine?
14. Describe one use of an alkali metal in everyday life.
15. What gas is produced during the reaction of an alkali metal with an acid?
16. Explain why Group 1 elements are not found in their pure form in nature.
17. What kind of flame test colours do Group 1 elements produce?
18. Describe how alkali metals tarnish in the air.
19. Why are alkali metals not used for structural purposes like building?
20. How do Group 1 elements compare to transition metals in terms of density?

Hard Level Questions

Advanced Concepts and Applications

1. Explain the trend in atomic radius as you go down Group 1.
2. Discuss the trend in ionisation energy in Group 1 elements.
3. Explain why francium is the most reactive Group 1 element.
4. Compare the reaction of lithium and potassium with water.
5. Explain why alkali metals are highly reactive with halogens.
6. Write the electron configuration for sodium and potassium.
7. Explain why Group 1 metals are good conductors of electricity.
8. Describe why potassium’s reactivity is higher than sodium’s.
9. What happens to the boiling point as you go down Group 1?
10. Discuss why Group 1 metals are often used in atomic clocks (cesium).
11. Describe the bonding and structure in alkali metal compounds.
12. Why do Group 1 metals form +1 ions?
13. Explain the effect of adding Group 1 metals to strong acids.
14. What is the impact of Group 1 elements on water pH?
15. Explain why francium is difficult to study in a laboratory.
16. Describe the shielding effect in Group 1 elements.
17. How does metallic bonding affect the properties of alkali metals?
18. Explain why the density of Group 1 metals generally increases down the group.
19. Discuss the reasons for using lithium in batteries over other alkali metals.
20. Explain the role of cesium in scientific applications.

Answers and Explanations

Easy Level Answers

1. Alkali metals – Group 1 elements are called alkali metals because they form alkaline solutions when they react with water.
2. Lithium, Sodium, Potassium
3. Na
4. They appear shiny but tarnish quickly due to reaction with air.
5. Solid
6. They form an alkaline solution and hydrogen gas – a characteristic reaction.
7. Hydrogen
8. To prevent reaction with oxygen and moisture in the air.
9. Soft compared to other metals.
10. Lithium
11. Due to reaction with oxygen in the air.
12. Lithium hydroxide and hydrogen
13. Not very dense
14. More reactive
15. Because they are less dense than water
16. Alkaline solution
17. Wear gloves and goggles to prevent contact with skin.
18. Red flame
19. One electron
20. A metal oxide

Medium Level Answers

1. They are called alkali metals because they form alkaline solutions (basic, with a pH greater than 7) when they react with water, producing metal hydroxides.
2. When lithium reacts with water, it fizzles and moves slowly across the surface. You may see bubbles as hydrogen gas is produced, but it’s not as vigorous as sodium or potassium.
3. Sodium reacts more vigorously with water compared to lithium, moving faster across the water and often forming a ball due to the heat released.
4. Potassium produces a lilac (light purple) flame when it burns, which is distinctive for this element.
5. Reactivity increases down the group because the outer electron is farther from the nucleus. This makes it easier for the atom to lose the outer electron, increasing reactivity.
6. 2K + 2H₂O → 2KOH + H₂ – Potassium reacts with water to produce potassium hydroxide and hydrogen gas.
7. Sodium reacts with oxygen to produce sodium oxide (Na₂O) and sometimes sodium peroxide (Na₂O₂) depending on the conditions.
8. Group 1 elements are dangerous to handle with bare hands because they react with moisture and oils on the skin, potentially causing burns.
9. To safely dispose of sodium, you can carefully add it to a large amount of water in a fume cupboard to allow it to fully react.
10. Freshly cut potassium appears shiny and silvery, but it tarnishes very quickly in the air, turning dull.
11. Potassium is more reactive than lithium because its outer electron is further from the nucleus, making it easier to lose during reactions.
12. The solution’s pH would be greater than 7, as the reaction produces sodium hydroxide, a strong base.
13. Lithium reacts with chlorine to produce lithium chloride (LiCl), a white crystalline salt.
14. Lithium is commonly used in rechargeable batteries due to its high energy density.
15. When an alkali metal reacts with an acid, it produces hydrogen gas. For example, sodium reacts with hydrochloric acid to produce sodium chloride and hydrogen.
16. Group 1 elements are so reactive that they are never found in their pure form in nature; they are always in compounds with other elements.
17. In flame tests, alkali metals produce distinct colours. For example, lithium shows red, sodium yellow, and potassium lilac.
18. Alkali metals tarnish in air as they react with oxygen. For example, sodium forms a dull layer of sodium oxide on the surface.
19. Alkali metals are soft and reactive, making them unsuitable for structural purposes like building.
20. Group 1 metals have much lower densities compared to transition metals, so they feel lighter.

Hard Level Answers

1. The atomic radius increases as you go down Group 1 because each element has an additional electron shell, placing the outer electron further from the nucleus.
2. Ionisation energy decreases down the group because the outer electron is further from the nucleus and shielded by more inner electrons, making it easier to remove.
3. Francium is the most reactive Group 1 element because it has the largest atomic radius and lowest ionisation energy, making it easier to lose its outer electron.
4. Potassium reacts more vigorously with water than lithium, producing a lilac flame and moving quickly, whereas lithium’s reaction is slower and less intense.
5. Alkali metals are highly reactive with halogens because they readily lose one electron, which halogens gain, forming stable ionic compounds like sodium chloride.
6. Sodium: 1s² 2s² 2p⁶ 3s¹; Potassium: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ – Both have one electron in their outer shell, contributing to their reactivity.
7. Group 1 metals are good conductors of electricity due to their free-moving outer electron, which can carry an electric current.
8. Potassium is more reactive than sodium because its outer electron is further from the nucleus and more easily lost.
9. The boiling point decreases as you go down Group 1 because the metallic bonds become weaker with increasing atomic size.
10. Cesium is used in atomic clocks because it has a precise frequency of vibration, making it ideal for accurate time measurement.
11. In alkali metal compounds, the bonding is ionic, where the metal atom donates an electron to form positive ions.
12. Group 1 metals form +1 ions because they have one electron in their outer shell, which they lose easily to achieve a stable electron configuration.
13. Adding Group 1 metals to strong acids produces hydrogen gas and a salt, e.g., Na + HCl → NaCl + H₂.
14. Group 1 elements increase the pH of water due to the formation of hydroxides, which are alkaline.
15. Francium is difficult to study because it is highly radioactive and exists only in trace amounts in nature.
16. The shielding effect increases as you go down Group 1, meaning the inner electrons shield the outer electron from the nucleus, making it easier to lose.
17. Metallic bonding in alkali metals involves a ‘sea of electrons,’ which makes them good conductors but also contributes to their softness.
18. Density generally increases down Group 1 because the atomic mass increases faster than the volume.
19. Lithium is used in batteries because it is lightweight and highly reactive, providing a good energy-to-weight ratio compared to other metals.
20. Cesium’s precise frequency makes it ideal for scientific applications like atomic clocks and certain types of spectroscopy.

This set of questions and answers provides a comprehensive review of Group 1 elements, tailored for Year 8 students studying for their Key Stage 3 exams. By working through these questions, students can deepen their understanding of the properties, reactions, and real-world applications of alkali metals.