Problem 39 - Chemistry and Chemical Reactivity

Question

When a potassium atom becomes a monatomic ion, how many electrons does it lose or gain? What noble gas atom has the same number of electrons as a potassium ion?

Step-by-Step Solution

Answer

Potassium loses 1 electron, and the potassium ion has the same electron configuration as argon.

Step 1: Identify the Electron Configuration of Potassium

Start by determining the electron configuration of a neutral potassium atom. Potassium (K) is element number 19 on the periodic table, which corresponds to having 19 electrons. Its configuration is \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^1 \].

Step 2: Determine Electron Change for Ion Formation

A potassium atom tends to lose one electron to achieve a stable electron configuration. Losing one electron means the potassium ion (K⁺) would now have an electron configuration of \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \], totaling 18 electrons.

Step 3: Identify the Noble Gas with the Same Electron Configuration

Compare the electron configuration of the potassium ion to that of the noble gases. Argon (Ar) has the electron configuration \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \], which is the same as the electron configuration of a K⁺ ion.

Key Concepts

Electron Configuration

Electron configuration is a way of representing how electrons are distributed within an atom's orbitals. These orbitals are divided into different levels or shells, denoted by the principal quantum numbers such as 1, 2, 3, etc. Each shell consists of subshells labeled as 's', 'p', 'd', and 'f', with varying capacities for holding electrons.
A neutral potassium atom, which is element number 19 on the periodic table, possesses 19 electrons. Thus, its electron configuration is expressed as \( 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^1 \). This means:

• 1s subshell holds 2 electrons
• 2s and 3s subshells hold 2 electrons each
• 2p and 3p subshells hold 6 electrons each
• 4s subshell holds 1 electron

The arrangement follows the Aufbau principle, which suggests electrons fill the lowest energy orbitals first before moving to higher ones. In essence, understanding electron configuration helps chemists predict how atoms interact in chemical reactions.

Monatomic Ion

A monatomic ion forms when a single atom gains or loses electrons, resulting in a charged entity. Potassium, for example, readily forms a monatomic ion by the loss of electrons.
When potassium (K) loses one electron, it transforms into a potassium ion \((K^+)\). This electron loss is driven by the atom's desire to achieve a stable electron configuration, typically seen in noble gases. By losing this single electron, the potassium transitions from having 19 electrons to just 18.
This ionization process is especially significant because it shows how elements achieve stability. Generally, metallic elements like potassium lose electrons to form cations, whereas non-metals gain electrons to become anions. For potassium, the resulting monatomic ion not only clarifies its role in reactions but also how it behaves in ionic compounds.

Noble Gas Electron Configuration

The concept of achieving a noble gas electron configuration is crucial for understanding atomic stability. Noble gases like helium, neon, and argon are known for their full valence shells, making them extremely stable and inert.
For potassium to achieve this stable configuration, it loses one electron and transitions from \( 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^1 \) to \( 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \). The potassium ion \((K^+)\) thus shares the same electron configuration as the noble gas argon (Ar).
This configuration offers insight into why elements behave the way they do in chemical reactions. It underscores the tendency of elements to stabilize by emulating the nearest noble gas electron configuration, guiding their electron gain, loss, or sharing processes. Understanding this concept explains why many chemical reactions occur and how compounds are formed.