Question

Explain why is sodium less reactive than potassium.

Short answer

Potassium is more reactive due to its larger atomic size and increased electron shielding, making its outer electron easier to remove.

Step-by-step solution

Understand Atomic Structure

Sodium (Na) and potassium (K) are both alkali metals, which means they have one electron in their outermost shell. Sodium has the atomic number 11, and potassium has the atomic number 19, meaning sodium has a configuration ending in 3s¹, while potassium ends in 4s¹.

Assess Atomic Size

Potassium's electrons are farther from the nucleus compared to sodium because potassium has an additional energy level. This increased atomic size contributes to the shielding effect, making it easier for the outer electron in potassium to escape.

Evaluate the Shielding Effect

In potassium, there are more inner electron shells than in sodium. These inner shells shield the outer electron from the attractive forces of the nucleus, making it easier to remove than in sodium, which has less shielding.

Compare Electron Affinity

The tendency of an atom to attract electrons decreases as the atomic number increases down a group in the periodic table. Therefore, compared to sodium, potassium's single outer electron is less tightly held, leading to higher reactivity.

Conclude Based on Reactivity

Since potassium's outer electron is easier to remove due to increased atomic size, greater shielding, and lower hold by the nucleus, it will react more vigorously than sodium when engaging in chemical reactions.

Key concepts

Understanding Atomic Structure of Alkali Metals

At the heart of understanding reactivity in alkali metals, such as sodium (Na) and potassium (K), is their atomic structure. Both of these metals belong to the group of alkali metals and share a common trait—they each have one electron in their outermost shell. This is known as the valence electron. For sodium, which has an atomic number of 11, the electron configuration ends in 3s¹. On the other hand, potassium, with an atomic number of 19, has a configuration that ends in 4s¹.

It's important to remember that having a single electron in the outer shell makes these metals very reactive, yet the layer or shell in which this electron resides can dramatically impact their reactivity levels. As we investigate further, it becomes apparent that this configuration difference between sodium and potassium is a key factor in understanding why potassium is more reactive than sodium.

The Role of Atomic Size in Reactivity

Atomic size is an essential concept when discussing the reactivity of elements. As you move down a group in the periodic table, the atomic size increases. This is because additional energy levels (or shells) are added as you progress down the group. Potassium, being below sodium in the periodic table, thus has a larger atomic size due to having an extra energy level.

With a larger atomic size, the outer electron in potassium is located further away from the nucleus compared to sodium. This increased distance leads to reduced nuclear attraction on the outer electron, making it easier for the electron to escape. As a result, potassium tends to react more readily than sodium because it requires less energy to lose its outer electron.

Impact of the Shielding Effect

The shielding effect plays a crucial role in determining how easily an atom can lose its outer electron. In essence, it describes how inner-shell electrons can shield the outer-shell electrons from the attractive pull of the nucleus. The more inner electron shells an atom has, the more effective this shielding effect becomes.

In potassium, which has more inner shells than sodium, the outermost electron experiences a significant shielding effect. This means the electron is less tightly held by the nucleus, as the inner electrons partially block the attractive forces of the nucleus. This makes it simpler for potassium to lose its outer electron, as compared to sodium, which experiences less shielding due to fewer inner electron shells.

Influence of Electron Affinity on Reactivity

Electron affinity is another factor influencing reactivity and refers to the ability of an atom to attract and hold onto an added electron. In the context of alkali metals, electron affinity is less about gaining electrons and more about the ease of losing them. As you move down a group in the periodic table, electron affinity decreases.

In this case, since potassium is further down the group from sodium, it has a lower electron affinity, meaning its outer electron is not as strongly held. This decreased attraction between the outer electron and the nucleus results in a higher tendency for this electron to be lost during a reaction. Ultimately, the lower electron affinity in potassium compared to sodium contributes to its greater reactivity. This explains why, when reacting in chemical processes, potassium will generally be more vigorous than sodium.