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 one electron and becomes like argon.

Step 1: Understanding Potassium Atom

A potassium atom, represented by the symbol \( K \), has an atomic number of 19. This means that a neutral potassium atom has 19 electrons.

Step 2: Forming a Potassium Ion

A potassium atom tends to lose electrons to form a stable ion. Specifically, it loses one electron to achieve stability.

Step 3: Charge of Potassium Ion

Once potassium loses one electron, it becomes a positively charged ion, \( K^+ \). This is because it initially had 19 protons and 19 electrons; losing one electron results in 18 electrons.

Step 4: Determining Equivalent Noble Gas

A potassium ion \( K^+ \) with 18 electrons shares the same electron configuration as the noble gas argon, which also has 18 electrons.

Key Concepts

Electron Configuration

The electron configuration of an atom describes the distribution of its electrons in different orbitals or energy levels. Each element has a unique arrangement based on its atomic number, which specifies the number of electrons. For a neutral potassium atom (symbolized by \( K \)), this is 19. Its electron configuration can be written based on its placement in the periodic table. Using standard notation, potassium has the configuration: \( 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 \).

• The first shell (1s) holds 2 electrons.
• The second shell (2s, 2p) holds 8 electrons.
• The third shell (3s, 3p) also holds 8 electrons.
• The fourth shell begins with one electron in the 4s orbital.

This arrangement shows that potassium has a single electron in its outermost shell, making it more likely to lose that electron and form a stable ion.

Potassium Ion

When a potassium atom forms an ion, it undergoes a change in its electron configuration. Since potassium is in Group 1 of the periodic table, it has one electron in its outermost shell (4s). This makes it eager to lose that lone electron to achieve a more stable state. By shedding this electron, potassium becomes a positively charged ion, known as \( K^+ \).

• This process leaves the ion with 18 electrons.
• The charge is +1 because it results in more protons than electrons.
• The loss of one electron brings it closer to the electron configuration of a noble gas.

Once potassium loses an electron, its electron configuration mirrors that of argon, and hence, it achieves stability through a similar electronic configuration.

Noble Gases

Noble gases are elements in Group 18 of the periodic table known for their stability and reluctance to react with other elements. This stability arises from their completely filled outer electron shells. For many atoms, achieving a noble gas electron configuration is synonymous with achieving stability.

Potassium ion \( K^+ \) reaches such stability by losing one electron, adopting the same electron configuration as the noble gas argon. Argon's electron arrangement is \( 1s^2 2s^2 2p^6 3s^2 3p^6 \), comprising a total of 18 electrons.

• Noble gases are often compared to other elements as a yardstick of stability.
• Many elements will gain or lose electrons to resemble the electron configuration of a noble gas.
• This process is central to the formation of stable ions through ionic bonding.

Thus, by achieving a noble gas configuration, the potassium ion becomes more energetically favorable and chemically stable, demonstrating the significance of noble gases in understanding chemical bonding and stability.