Which alkali metal, based on ionization energies, would you expect to undergo the most exothermic reaction with chlorine gas?

Name: Chemistry: A Molecular Approach
Author: Tro
ISBN: 9780134112831

Verified step by step guidance

Identify the alkali metals in the periodic table. These include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs).

Understand that ionization energy is the energy required to remove an electron from an atom. Alkali metals have low ionization energies, which decrease as you move down the group.

Recognize that a lower ionization energy means the metal can more easily lose an electron to form a cation, which is a key step in reacting with chlorine gas to form a salt.

Consider that the most exothermic reaction will occur with the alkali metal that can most easily lose its electron, which corresponds to the metal with the lowest ionization energy.

Determine which alkali metal has the lowest ionization energy by looking at periodic trends, noting that ionization energy decreases down the group, making cesium (Cs) the most likely candidate for the most exothermic reaction with chlorine gas.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom or ion in its gaseous state. For alkali metals, which have one valence electron, this energy is relatively low, allowing them to easily lose that electron and form positive ions. The lower the ionization energy, the more reactive the metal, particularly in reactions with halogens like chlorine.

Reactivity of Alkali Metals

Alkali metals (Group 1 elements) are known for their high reactivity, which increases down the group. This is due to the decreasing ionization energy as the atomic size increases, making it easier for these metals to lose their outermost electron. When reacting with halogens, such as chlorine, the most reactive alkali metal will typically form a more stable ionic compound, releasing energy in the process.

Exothermic Reactions

An exothermic reaction is a chemical reaction that releases energy, usually in the form of heat, to the surroundings. In the context of alkali metals reacting with chlorine gas, the formation of ionic bonds between the metal cation and the chloride anion releases significant energy. The more exothermic the reaction, the more stable the resulting compound, which is influenced by the reactivity of the alkali metal involved.