Yes, potassium is more reactive than lithium. This heightened reactivity is a fundamental characteristic of alkali metals as you move down Group 1 of the periodic table.
Understanding Alkali Metal Reactivity
Alkali metals, including lithium (Li), sodium (Na), and potassium (K), are known for their high reactivity, especially with non-metals like oxygen and water. This reactivity primarily stems from their atomic structure. Each alkali metal atom has only one electron in its outermost shell, which it readily loses to form a positive ion. The ease with which this electron is lost determines the metal's reactivity.
Why Potassium is More Reactive
As you descend Group 1 from lithium to potassium:
- Increasing Atomic Size: Potassium atoms are significantly larger than lithium atoms.
- Increased Shielding: The valence electron in potassium is further from the nucleus and is more shielded by inner electron shells.
- Lower Ionization Energy: Due to the increased distance and shielding, the electrostatic attraction between the nucleus and the outermost electron is weaker in potassium. Consequently, less energy is required to remove this electron, making potassium more eager to react and form compounds.
This trend is evident in how quickly these metals react with common substances. For instance, potassium tarnishes almost instantly upon exposure to air, making it difficult to observe its natural shiny metallic luster. This rapid tarnishing is strong evidence of potassium's higher reactivity compared to both lithium and even sodium.
Comparative Reactivity: Lithium vs. Potassium
The differences in reactivity between lithium and potassium are noticeable in their reactions with air and water.
Table: Reactivity Comparison of Lithium and Potassium
| Feature | Lithium (Li) | Potassium (K) |
|---|---|---|
| Atomic Size | Smaller | Larger |
| Ionization Energy | Higher | Lower |
| Reaction with Oxygen | Reacts steadily, forms lithium oxide. | Reacts extremely rapidly, often explosively, tarnishing almost instantly; forms potassium superoxide. |
| Reaction with Water | Reacts steadily, fizzes, floats, does not melt. | Reacts violently, often explosively, producing a lilac flame; melts into a sphere and darts across the surface. |
| General Reactivity | Least reactive alkali metal. | Highly reactive, more so than lithium and sodium. |
Practical Insights and Storage
Due to their high reactivity, alkali metals like potassium and lithium must be stored carefully to prevent accidental reactions.
- Potassium is typically stored under oil or in an inert atmosphere (like argon) to prevent its rapid reaction with oxygen and moisture in the air. Its quick tarnishing indicates its need for strict isolation from the environment.
- Lithium, while less reactive than potassium, is also stored under mineral oil or in a dry environment to prevent it from reacting with atmospheric components over time.
The enhanced reactivity of potassium makes it valuable in specific industrial applications, though its handling requires stringent safety protocols.
