Question

Explain, in terms of ionization energies, why potassium is more reactive than sodium.

Short answer

Potassium is more reactive than sodium because potassium has a lower ionization energy than sodium. This means that potassium loses its outermost electron more readily than sodium, which increases its reactivity.

Step-by-step solution

Understanding What Reactivity Is

Reactivity refers to the ability of an element to lose or gain electrons and participate in chemical reactions. An element is considered more reactive if it can lose or gain electrons more easily.

Comparing the Atomic Structure of Potassium and Sodium

Potassium (K) is in Period 4 and Group 1 (alkali metals) on the periodic table, while sodium (Na) is directly above it in Period 3. This means that the extra electron in potassium is farther away from the nucleus compared to that of sodium. This is because as you move down the groups in the periodic table, the number of energy levels or shells increases, hence the outermost electron in potassium is farther away from the attraction of the nucleus than in sodium.

Understanding Ionization Energy

Ionization energy is the energy needed to remove an electron from a gaseous atom. The farther the electron is from the nucleus, the less energy is required to remove it due to reduced electromagnetic force of attraction. Thus, potassium should have a smaller ionization energy than sodium.

Connecting Ionization Energy to Reactivity

Elements with lower ionization energies are usually more reactive because these atoms can lose their outermost electron more readily, enabling them to participate in chemical reactions more readily. Since potassium, being farther from the nucleus, requires less energy (has low ionization energy) to remove its outermost electron than sodium, potassium is more reactive than sodium.

Conclusion

So, potassium is more reactive than sodium because it has a lower ionization energy, indicating that potassium can lose its outermost electron more readily than sodium, making it more likely to engage in chemical reactions.

Key concepts

Reactivity

Reactivity in chemistry often describes how quickly and strongly an element can undergo a chemical change. For alkali metals like sodium (Na) and potassium (K), reactivity is linked to their ability to lose electrons.
As you move down the group in the periodic table, the reactivity of alkali metals increases. This increase is because the outermost electron is located in a higher energy level or shell, which is farther from the nucleus.
The distance of the outer electron from the nucleus makes it easy for these elements to lose it, thus enhancing their reactivity. In simpler terms, the weaker force between the nucleus and the outer electron in elements further down the group, like potassium, allows them to more readily participate in chemical reactions to achieve a stable electron configuration.

Chemical Reactions

Chemical reactions occur when substances interact and transform into new substances. During these reactions, the atoms of the elements or compounds rearrange themselves to form different products.
For alkali metals, these reactions often involve the metal losing an electron and reacting with other more electronegative elements or compounds. The ability to readily lose an electron means that alkali metals are highly reactive and often react explosively, especially with water.
When potassium reacts with water, it loses its outer electron quickly, forming potassium hydroxide and hydrogen gas, which can ignite due to the heat of the reaction. This rapid reaction is a classic display of how the reactivity of an element can lead to vigorous chemical activity.

Alkali Metals

Alkali metals include the elements found in group 1 of the periodic table, such as lithium, sodium, and potassium. These metals are known for their high reactivity and distinctive physical properties.
One major property of alkali metals is their tendency to lose their single outer electron easily. This property stems from their large atomic radius and low ionization energy. The atomic radius increases as you move down the group, making the outer electron less tightly held by the nucleus.

• These metals are soft and can often be cut with a knife.
• They have low melting and boiling points compared to most other metals.
• Their reactions with water are highly exothermic, releasing hydrogen gas.

Because of these characteristics, caution is needed when handling alkali metals like potassium, as their reactive nature can lead to spontaneous and potentially dangerous chemical reactions.