Question

Which of the following alkali metals has the lowest melting point?

• A. Cs
• B. Li
• C. Na
• D. K

Hint:

Remember that in Group 1, the metal with the largest atomic size will have the lowest melting point due to weaker metallic bonding.

Answer 1

The Correct Option is A

Step 1: Concept
The melting points of alkali metals decrease as you move down the group in the periodic table. This trend is due to the increasing atomic size, which leads to weaker metallic bonds.

Step 2: Meaning
Atomic size increases from top to bottom within a group because the outermost electrons are farther from the nucleus. As the atomic size increases, the attraction between the metal ions and the delocalized electrons decreases, resulting in lower melting points.

Step 3: Analysis
Lithium (Li) is at the top of Group 1. Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), and Francium (Fr) are successively larger as you move down the group. The metallic bond strength decreases with increasing atomic size, leading to lower melting points for metals further down the group. To compare Cs, Li, Na, and K: Cs has a larger atomic radius compared to Li, Na, and K due to its position in the periodic table. As a result, the metallic bonds in cesium are weaker than those in lithium, sodium, or potassium. Therefore, cesium will have the lowest melting point among these alkali metals.

Step 4: Conclusion
The melting points of alkali metals decrease as you move down the group. Cesium (Cs) has the largest atomic radius and thus the weakest metallic bonds, leading to its lowest melting point. Final Answer: (A)