Short Answer:

Potassium is more reactive than sodium because its outermost electron is farther from the nucleus and is more easily lost. This makes potassium more willing to react with water, acids, or other substances.

As a result, potassium reacts more vigorously than sodium, producing more heat and hydrogen gas when it reacts with water. This trend is observed in alkali metals, where reactivity increases down the group in the periodic table.

Detailed Explanation:

Reactivity of Potassium and Sodium

Potassium (K) and sodium (Na) are both alkali metals in Group 1 of the periodic table. Alkali metals have one electron in their outermost shell, which they tend to lose to form positive ions. The reactivity of these metals depends on how easily this outer electron can be removed.

Atomic Structure Influence

1. Electron Configuration:
   • Sodium: 1s² 2s² 2p⁶ 3s¹
   • Potassium: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
   • Potassium’s outermost electron is in the 4th shell, farther from the nucleus than sodium’s 3rd shell electron.
2. Distance from Nucleus:
   • The farther the outer electron is from the positively charged nucleus, the weaker the attraction.
   • Weaker attraction makes it easier for potassium to lose its outer electron compared to sodium.
3. Shielding Effect:
   • Inner electrons shield the outer electron from the nucleus.
   • Potassium has more inner electron shells than sodium, increasing shielding and reducing nuclear pull on the outer electron.

Periodic Trend in Reactivity

• In Group 1 (alkali metals), reactivity increases down the group.
• Lithium < Sodium < Potassium < Rubidium < Cesium
• The trend is due to the increasing distance and shielding, which makes the outer electron easier to remove.

Reactivity with Water

• Sodium reacts with water to produce sodium hydroxide and hydrogen:
  2Na + 2H₂O → 2NaOH + H₂
• Potassium reacts more vigorously:
  2K + 2H₂O → 2KOH + H₂
• Potassium reaction is faster and often produces sparks and more heat, showing higher reactivity.

Other Factors

1. Ionization Energy:
   • Potassium has lower ionization energy than sodium, meaning it requires less energy to remove its outer electron.
2. Physical Properties:
   • Potassium is softer and can be cut easily, showing its readiness to react.

Importance of Reactivity Differences

• Helps predict reactions in chemistry experiments and industrial processes.
• Indicates the need for careful handling of potassium due to its high reactivity.
• Demonstrates periodic trends and the behavior of alkali metals.

Conclusion:

Potassium is more reactive than sodium because its outermost electron is farther from the nucleus, experiences weaker attraction, and is easier to remove. This increased reactivity is reflected in its vigorous reaction with water and other substances. Understanding this trend helps in predicting chemical behavior and handling alkali metals safely.