5.3 Comparison of Reactivity of Group 1 and Group 2 Elements

Group 1 (alkali metals) and Group 2 (alkaline earth metals) are both located on the left side of the periodic table and are known for being highly reactive metals. However, there are important differences in their reactivity. Understanding these differences helps us predict how they will behave in chemical reactions.

Main Idea

The main idea is that Group 1 elements are more reactive than Group 2 elements in the same period. This is due to their lower ionization energies, which make it easier for them to lose their single valence electron compared to the two valence electrons of Group 2 elements.

Core Concept

The core concept is that reactivity depends on ionization energy. The lower the ionization energy, the easier it is for a metal to lose electrons and form positive ions, and the more reactive the metal is.

• Group 1 elements have one valence electron in an s-orbital.
• Group 2 elements have two valence electrons in an s-orbital.

Removing one electron from a Group 1 atom is easier than removing two electrons from a Group 2 atom in the same period. Also, Group 1 elements have a larger atomic radius and a lower effective nuclear charge on their valence electron, so the electron is less tightly held. This is why Group 1 metals are more reactive.

Detailed Explanation

Comparison of Ionization Energies

The textbook states that reactivity of an element depends upon the ionization energy. Smaller the value of ionization energy, greater is the reactivity.

• Alkaline earth metals (Group 2) have higher ionization energy as compared to alkali metals (Group 1). It is because of their smaller size and greater attraction of electrons towards the nucleus.
• Group II elements are less reactive than Group I elements in the same period because of the low ionization energy of Group I elements as compared to Group II.

Comparison of Reactivity with Water

The difference in reactivity is most clearly seen in their reactions with water.

- Alkali metals (Group 1) react vigorously with water. The reaction is so vigorous that the evolved hydrogen catches fire. Na_{(s)} + 2H_2O_{(l)} → 2NaOH_{(aq)} + H_{2(g)} - Alkaline earth metals (Group 2) react more slowly with water. Ca_{(s)} + 2H_2O_{(l)} → Ca(OH)_{2(aq)} + H_{2(g)}

Comparison as Reducing Agents

- Alkali metals are good reducing agents compared to alkaline earth metals because they possess smaller values of ionization energy. This means they lose electrons more readily, making them stronger reducing agents.

Summary of Differences

Intermediate Level

The reactivity of a metal is determined by its ability to lose electrons, which is measured by its ionization energy. Group 1 elements have lower ionization energies than Group 2 elements in the same period. This is because Group 1 atoms have a larger atomic radius and a lower effective nuclear charge, so their single valence electron is less tightly held. As a result, Group 1 metals lose electrons more easily and are more reactive. This is evident in their reactions with water: Group 1 metals react vigorously, often producing enough heat to ignite the hydrogen gas, while Group 2 metals react more slowly. Group 1 metals are also stronger reducing agents because they can donate electrons more readily.

Important Points

• - Group 1 (Alkali Metals): 1 valence electron, lower ionization energy, more reactive.
• - Group 2 (Alkaline Earth Metals): 2 valence electrons, higher ionization energy, less reactive.
• - Reactivity: Group 1 > Group 2 (in the same period).
• - Reaction with water: Group 1 is vigorous (H₂ may ignite); Group 2 is slower.
• - Reducing agents: Group 1 metals are stronger reducing agents.
• - Reason: Group 1 has lower ionization energy.

Remember

• - Group 1 is more reactive than Group 2.
• - Group 1 has 1 valence electron, Group 2 has 2.
• - Lower ionization energy = higher reactivity.
• - Group 1 metals are stronger reducing agents.
• - Na reacts vigorously with water; Ca reacts more slowly.
• - Group 1 elements are on the far left of the periodic table.

Common Mistakes

• - Thinking that Group 2 metals are more reactive because they have more electrons to lose. It's the opposite: it's easier to lose one electron than two, so Group 1 is more reactive.
• - Confusing the reactivity of Group 1 and Group 2 with their abundance. Reactivity is a chemical property, while abundance is a physical occurrence.
• - Forgetting that the comparison is for elements in the same period. The trend is valid when comparing elements in the same row of the periodic table.
• - Assuming that all Group 1 metals react with water in the same way. The reactivity increases down the group (Li to Cs), but all are more reactive than their Group 2 counterparts.
• - Thinking that Group 2 metals are not reactive at all. They are still quite reactive, just less so than Group 1 metals.

Quick Revision

Group 1 (alkali metals) and Group 2 (alkaline earth metals) are both reactive, but Group 1 elements are more reactive than Group 2 elements in the same period. This is because Group 1 elements have only one valence electron and a lower ionization energy, making it easier for them to lose that electron and form positive ions. Group 2 elements have two valence electrons and a higher ionization energy, so they are less reactive. This difference is evident in their reactions with water: Group 1 metals react vigorously (often igniting the hydrogen produced), while Group 2 metals react more slowly. Group 1 metals are also stronger reducing agents.

60-Second Revision

Group 1 elements are more reactive than Group 2 elements because they have lower ionization energies. It is easier to lose one valence electron (Group 1) than two (Group 2). Group 1 metals react more vigorously with water and are stronger reducing agents. The order of reactivity is Group 1 > Group 2.

Frequently Asked Questions (FAQs)

Q1. How do group 1 metals differ from Group 2 metals? Answer: Group 1 metals (alkali metals) have one valence electron and are more reactive. They have lower ionization energies and react vigorously with water. Group 2 metals (alkaline earth metals) have two valence electrons and are less reactive. They have higher ionization energies and react more slowly with water. Group 1 metals are also stronger reducing agents.

Q2. Why are Group 1 elements more reactive than Group 2 elements? Answer: Group 1 elements are more reactive because they have lower ionization energies. They need to lose only one electron to achieve a stable noble gas configuration, while Group 2 elements need to lose two. The single valence electron in Group 1 is also less tightly held due to the larger atomic radius and lower effective nuclear charge. Therefore, Group 1 metals lose electrons more easily and are more reactive.

Q3. Compare the reactions of Group 1 and Group 2 metals with water. Answer: Group 1 metals react vigorously with water, producing hydrogen gas and a metal hydroxide. The reaction is often exothermic enough to ignite the hydrogen. Group 2 metals react more slowly with water. For example, sodium (Group 1) reacts violently with cold water, while calcium (Group 2) reacts more gently, and magnesium (Group 2) only reacts with steam.

Q4. Which group is a stronger reducing agent: Group 1 or Group 2? Answer: Group 1 metals are stronger reducing agents. This is because they have lower ionization energies and lose electrons more readily than Group 2 metals. A stronger reducing agent is one that is more easily oxidized (loses electrons).

Q5. Why do Group 1 elements have lower ionization energies than Group 2 elements? Answer: Group 1 elements have a larger atomic radius and a lower effective nuclear charge than Group 2 elements in the same period. Their single valence electron is further from the nucleus and is less tightly held, so it requires less energy to remove it.

Q6. What is the trend in reactivity down Group 1? Answer: The reactivity of Group 1 metals increases down the group. This is because the ionization energy decreases as the atomic radius increases, making it easier to lose the valence electron. For example, potassium is more reactive than sodium, which is more reactive than lithium.

Q7. What is the trend in reactivity down Group 2? Answer: The reactivity of Group 2 metals also increases down the group, for the same reason: the ionization energy decreases as the atomic radius increases. However, Group 2 metals are still less reactive than Group 1 metals in the same period.

Q8. Give an example of a reaction that shows Group 1 is more reactive than Group 2. Answer: The reaction with water is a classic example. Sodium (Group 1) reacts vigorously with cold water, producing hydrogen gas that can ignite. Calcium (Group 2) reacts with cold water but much more slowly, and the hydrogen does not usually ignite.

Q9. Are Group 1 metals better oxidizing agents or reducing agents? Answer: Group 1 metals are better reducing agents. They are easily oxidized (lose electrons) and cause other substances to be reduced. They are not good oxidizing agents because they do not readily gain electrons.

Multiple Choice Questions (MCQs)

Q1. Which group of elements is more reactive? A. Group 1 B. Group 2 C. Group 17 D. Group 18 Correct Answer: A Explanation: Group 1 elements (alkali metals) are more reactive than Group 2 elements because they have lower ionization energies and lose their single valence electron more easily.

Q2. Why are Group 1 elements more reactive than Group 2 elements? A. They have more valence electrons. B. They have lower ionization energies. C. They have higher atomic masses. D. They have higher densities. Correct Answer: B Explanation: Group 1 elements have lower ionization energies, meaning it is easier for them to lose their valence electron and form positive ions, making them more reactive.

• Q3. How many valence electrons do Group 2 elements have?
• A. 1
• B. 2
• C. 3
• D. 4
• Correct Answer: B
• Explanation: Group 2 elements have two valence electrons in their outermost s subshell.

• Q4. Which of the following reactions is more vigorous?
• A. Sodium with water
• B. Calcium with water
• C. Magnesium with water
• D. Beryllium with water
• Correct Answer: A
• Explanation: Sodium (Group 1) reacts more vigorously with water than calcium or magnesium (Group 2). Beryllium does not react with water.

• Q5. Which group of metals is a stronger reducing agent?
• A. Group 1
• B. Group 2
• C. Group 17
• D. Group 18
• Correct Answer: A
• Explanation: Group 1 metals are stronger reducing agents because they have lower ionization energies and lose electrons more readily.

• Q6. What is the trend in reactivity down Group 1?
• A. Increases
• B. Decreases
• C. Remains constant
• D. Is unpredictable
• Correct Answer: A
• Explanation: Reactivity increases down Group 1 because the ionization energy decreases, making it easier to lose the valence electron.

• Q7. What is the trend in reactivity down Group 2?
• A. Increases
• B. Decreases
• C. Remains constant
• D. Is unpredictable
• Correct Answer: A
• Explanation: Reactivity increases down Group 2 for the same reason: ionization energy decreases as the atomic radius increases.

• Q8. Which of the following statements is true?
• A. Group 1 metals are less reactive than Group 2 metals.
• B. Group 2 metals are stronger reducing agents than Group 1 metals.
• C. Group 1 metals have higher ionization energies than Group 2 metals.
• D. Group 1 metals are more reactive than Group 2 metals.
• Correct Answer: D
• Explanation: Group 1 metals are more reactive than Group 2 metals due to their lower ionization energies.

• Q9. Which Group 1 metal reacts most vigorously with water?
• A. Lithium
• B. Sodium
• C. Potassium
• D. Cesium
• Correct Answer: D
• Explanation: Reactivity increases down Group 1, so cesium (Cs) is the most reactive and reacts most vigorously with water.

Q10. Why do Group 1 metals have lower ionization energies than Group 2 metals? A. They have a larger atomic radius and lower effective nuclear charge. B. They have a smaller atomic radius and higher effective nuclear charge. C. They have more protons in the nucleus. D. They have more neutrons in the nucleus. Correct Answer: A Explanation: Group 1 metals have a larger atomic radius and a lower effective nuclear charge, so their valence electron is less tightly held and easier to remove.

Multiple Choice Questions (MCQs)

• Q1. Which group is more reactive?
• A. Group 1
• B. Group 2
• C. Group 17
• D. Group 18
• Correct Answer: A
• Explanation: Group 1 elements (alkali metals) are more reactive than Group 2 elements due to lower ionization energies.

• Q2. Why are Group 1 elements more reactive than Group 2 elements?
• A. They have more valence electrons.
• B. They have lower ionization energies.
• C. They have higher atomic masses.
• D. They have higher densities.
• Correct Answer: B
• Explanation: Group 1 elements have lower ionization energies, so they lose their valence electron more easily, making them more reactive.

• Q3. How many valence electrons do Group 1 elements have?
• A. 1
• B. 2
• C. 3
• D. 4
• Correct Answer: A
• Explanation: Group 1 elements have one valence electron in their outermost s subshell.

• Q4. Which reaction is more vigorous?
• A. Sodium with water
• B. Calcium with water
• C. Magnesium with water
• D. Beryllium with water
• Correct Answer: A
• Explanation: Sodium (Group 1) reacts more vigorously with water than calcium or magnesium (Group 2).

• Q5. Which group is a stronger reducing agent?
• A. Group 1
• B. Group 2
• C. Group 17
• D. Group 18
• Correct Answer: A
• Explanation: Group 1 metals are stronger reducing agents because they have lower ionization energies and lose electrons more readily.

• Q6. What is the trend in reactivity down Group 1?
• A. Increases
• B. Decreases
• C. Remains constant
• D. Is unpredictable
• Correct Answer: A
• Explanation: Reactivity increases down Group 1 because the ionization energy decreases, making it easier to lose the valence electron.

• Q7. What is the trend in reactivity down Group 2?
• A. Increases
• B. Decreases
• C. Remains constant
• D. Is unpredictable
• Correct Answer: A
• Explanation: Reactivity increases down Group 2 for the same reason: ionization energy decreases as the atomic radius increases.

• Q8. Which of the following statements is true?
• A. Group 1 metals are less reactive than Group 2 metals.
• B. Group 2 metals are stronger reducing agents than Group 1 metals.
• C. Group 1 metals have higher ionization energies than Group 2 metals.
• D. Group 1 metals are more reactive than Group 2 metals.
• Correct Answer: D
• Explanation: Group 1 metals are more reactive than Group 2 metals due to their lower ionization energies.

• Q9. Which Group 1 metal reacts most vigorously with water?
• A. Lithium
• B. Sodium
• C. Potassium
• D. Cesium
• Correct Answer: D
• Explanation: Reactivity increases down Group 1, so cesium (Cs) is the most reactive and reacts most vigorously with water.

Q10. Why do Group 1 metals have lower ionization energies than Group 2 metals? A. They have a larger atomic radius and lower effective nuclear charge. B. They have a smaller atomic radius and higher effective nuclear charge. C. They have more protons in the nucleus. D. They have more neutrons in the nucleus. Correct Answer: A Explanation: Group 1 metals have a larger atomic radius and a lower effective nuclear charge, so their valence electron is less tightly held and easier to remove.