Reactivity with water

Definition

Reactivity with water refers to the ability of certain chemical elements, particularly metals, to react with water to form new substances, often releasing gases or producing hydroxides. In the context of group 1 and 2 elements, this property highlights the trends in their reactivity as one moves down the groups in the periodic table, showcasing increasing reactivity due to the decreasing ionization energy and the increasing size of the atoms.

5 Must Know Facts For Your Next Test

1. Alkali metals react vigorously with water, producing hydrogen gas and a corresponding alkali metal hydroxide that is highly soluble in water.
2. The reactivity of alkali metals with water increases down the group, with lithium reacting slowly while cesium reacts explosively.
3. Alkaline earth metals also react with water but typically require higher temperatures for the reaction to occur; beryllium does not react at all with water under normal conditions.
4. The general equation for the reaction of an alkali metal with water can be represented as: $$2M + 2H_2O \rightarrow 2MOH + H_2$$, where M is the alkali metal.
5. The reactivity trends are influenced by atomic size and ionization energy; as atomic size increases down a group, the outer electrons are further from the nucleus and more easily lost.

Review Questions

• Compare the reactivity of alkali metals and alkaline earth metals with water and explain why there are differences.
  • Alkali metals are generally much more reactive with water than alkaline earth metals. This difference arises because alkali metals have a single electron in their outer shell, which they can lose easily when reacting with water. In contrast, alkaline earth metals have two valence electrons, which makes their reactions less vigorous and often requires higher temperatures. As one moves down each group, both types of metals become more reactive due to decreasing ionization energy, but this trend is more pronounced in alkali metals.
• Explain how the structure of alkali and alkaline earth metals affects their reactivity with water.
  • The structure of both alkali and alkaline earth metals plays a significant role in their reactivity with water. Alkali metals have one electron in their outermost shell, leading to lower ionization energies compared to alkaline earth metals that have two. This means alkali metals can lose their single outer electron more readily than alkaline earth metals can lose both of theirs. Furthermore, as you go down each group, atomic size increases which reduces the hold that the nucleus has on these outer electrons, making them even more reactive when interacting with water.
• Evaluate how understanding reactivity with water contributes to predicting the behavior of group 1 and 2 elements in various chemical reactions.
  • Understanding reactivity with water provides insight into how group 1 and 2 elements will behave in different chemical contexts. For instance, knowing that alkali metals will vigorously produce hydrogen gas when reacting with water allows chemists to anticipate potential hazards in experiments or industrial processes involving these elements. Additionally, recognizing that alkaline earth metals may require specific conditions to react informs decision-making about their use in applications like alloys or catalysts. By analyzing these reactivity patterns, chemists can better predict outcomes in synthesis or during reactions under varying environmental conditions.

Related terms

alkali metals:

The group 1 elements, such as lithium, sodium, and potassium, known for their high reactivity, particularly with water, where they form alkaline hydroxides and hydrogen gas.

alkaline earth metals: The group 2 elements, including magnesium and calcium, that also react with water but typically at a slower rate compared to alkali metals, producing hydroxides and hydrogen gas.

hydroxide: A negatively charged ion (OH⁻) that is formed when metals react with water, resulting in the creation of metal hydroxides.