Question

Potassium is a highly reactive metal while argon is an inert gas. Explain this difference based on their electron configurations.

Short answer

Potassium is highly reactive because it has one valence electron that is easily lost to achieve a stable configuration. Argon is inert as it already has a full outer shell and does not need to gain or lose electrons.

Step-by-step solution

Identify the Electron Configuration of Potassium

The first step is to determine the electron configuration of Potassium (K), which is an alkali metal. Potassium's atomic number is 19, meaning it has 19 electrons. The electron configuration is written as 1s2 2s2 2p6 3s2 3p6 4s1, with the last electron in the 4s orbital.

Identify the Electron Configuration of Argon

Next, determine the electron configuration of Argon (Ar), which is a noble gas. Argon's atomic number is 18, indicating it has 18 electrons. Its electron configuration is 1s2 2s2 2p6 3s2 3p6, with a complete octet in the outer shell.

Compare the Reactivity Based on Electron Configurations

Potassium has a single electron in its outermost energy level (4s1), which it tends to lose easily to achieve a stable noble gas configuration (like Argon). This loss of the single electron requires minimal energy making potassium highly reactive. In contrast, argon has a full outer shell (3p6), which makes it stable and not inclined to react with other elements, thus being inert.

Key concepts

Potassium Chemical Properties

Potassium, found in group 1 of the periodic table, is characterized by its notable reactivity. This active behavior can primarily be attributed to its electron configuration, \( [Ar] 4s^1 \), which leaves it with one electron in its outermost shell. This solitary electron possesses a relatively low ionization energy, meaning that it doesn't require much energy to remove it. As a result, potassium readily loses this electron to form a positive ion, \( K^+ \),thus reaching the stable electron configuration of the noble gas argon.
In the presence of water, it reacts vigorously, producing potassium hydroxide and hydrogen gas. Due to such chemical properties, potassium plays a crucial role in various industrial processes.

Argon Electron Configuration

Argon belongs to group 18 of the periodic table, which comprises the noble gases. Looking at argon's electron configuration, it reads as \( 1s^2 2s^2 2p^6 3s^2 3p^6 \). This configuration highlights a complete octet in its outer shell, aligning with the \( 'octet rule' \) that suggests atoms tend to be stable with eight electrons in their valence shell. This complete outer shell negates the need for argon to gain or lose electrons, rendering it nonreactive or inert. Its use in lighting and welding takes advantage of this stability, as it provides an inert atmosphere that doesn't react with the materials involved.

Alkali Metals Reactivity

Alkali metals, located in group 1 of the periodic table, are known for their significant reactivity. This trait stems from their similar electron configurations which feature a single valence electron that can be easily removed to achieve the electron configuration of a noble gas.
As you progress down the group, the reactivity of alkali metals increases. This trend is due to the valence electron being further from the nucleus and less tightly held, allowing for more straightforward electron loss.
Consequently, elements like lithium, sodium, and potassium react exothermically upon contact with water, often vigorously enough to ignite the produced hydrogen gas.

Noble Gases Inertness

The noble gases, inhabitants of group 18 in the periodic table, showcase an inherent inertness or lack of reactivity. This characteristic arises from their filled valence shells, which obey the 'octet rule' for attaining stability.
Since they already possess a stable electron arrangement, noble gases like helium, neon, argon, and others do not typically form chemical bonds with other elements. Their inertness makes them ideal for applications that require non-reactive environments such as light bulbs, where they prevent the oxidation of the filament, and in shielding gases for welding, preventing unwanted chemical reactions.