Why are alkali metals so reactive? (+ Video)

Alkali metals are highly reactive because they have a single valence electron in their outermost energy level, which is easily lost. This electron configuration makes them eager to give away this electron and achieve a stable, noble gas configuration, resulting in their strong reactivity with other elements. ¹

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Explanation: Why are alkali metals reactive?

Alkali metals are highly reactive due to the presence of a single valence electron in their outermost energy level (also known as the valence shell). This electron configuration makes them highly likely to lose this outer electron and form a positive ion with a stable electron configuration. ²

Here are a few reasons why alkali metals exhibit such reactivity:

• Low ionization energy: Alkali metals have low ionization energies, which means it requires relatively little energy to remove their outermost electron. ³ The low ionization energy allows them to readily lose this electron and form a positively charged ion (cation).
• Large atomic size: Alkali metals have relatively large atomic sizes due to the presence of only one electron in their outermost energy level. ⁴ The large size leads to a weak attraction between the valence electron and the positively charged nucleus, making it easier for the electron to be removed.
• Formation of stable octet: By losing their single valence electron, alkali metals achieve a stable electron configuration similar to the noble gas configuration of the preceding noble gas element. This stable octet configuration (eight electrons in the outermost shell) increases the stability of the resulting cation.
• Electrostatic attraction with other atoms: Once alkali metals lose their valence electron and form a positive ion, they are strongly attracted to other negatively charged species, such as nonmetals or polyatomic ions. This electrostatic attraction leads to the formation of ionic compounds, where the alkali metal cation is surrounded by negatively charged ions. ⁵

Due to their reactivity, alkali metals are highly reactive with water and air, and they must be handled with care. They can react vigorously with water, releasing hydrogen gas and forming alkali metal hydroxides. They also readily oxidize in air, forming oxides or hydroxides on their surfaces.

Vigorous reaction of alkali metals with water

The reaction of alkali metals with water is highly vigorous due to their high reactivity. When alkali metals, such as sodium or potassium, come into contact with water, they undergo a rapid and exothermic reaction. ⁶

Here’s a simplified explanation of the reaction:

• Upon contact with water, the alkali metal reacts with the water molecules.
• The metal atom loses its outermost valence electron, forming a positively charged alkali metal ion (cation).
• The released electron combines with water molecules, producing hydrogen gas (H₂) and hydroxide ions (OH⁻).
• The alkali metal cation and hydroxide ions combine to form an alkali metal hydroxide compound.

The reaction is highly exothermic, meaning it releases a significant amount of heat. ⁷ This heat, combined with the rapid release of hydrogen gas, causes the reaction to be highly energetic and sometimes even explosive. The reaction of alkali metals with water is a classic demonstration of their reactivity, but it’s important to note that it can be hazardous and should be conducted with caution.

Other examples showing higher reactivity of alkali metals

Here are a few examples that illustrate the higher reactivity of alkali metals:

Reactivity with water: Alkali metals, such as sodium (Na) and potassium (K), react vigorously with water. ^{8 9} When sodium is placed in water, it reacts violently, producing hydrogen gas and sodium hydroxide:

2Na + 2H₂O -> 2NaOH + H₂

The reaction is highly exothermic and releases hydrogen gas rapidly. The reactivity increases as you move down the group, with potassium being even more reactive than sodium.

Reaction with oxygen: Alkali metals readily react with oxygen in the air, resulting in the formation of metal oxides. ¹⁰ For example, when potassium is exposed to air, it quickly forms potassium oxide:

4K + O₂ -> 2K₂O

This reaction is exothermic and can even cause the alkali metal to ignite. The reactivity with oxygen also increases as you go down the group.

Reaction with halogens: Alkali metals react vigorously with halogens, such as chlorine (Cl) or bromine (Br), to form alkali metal halides. ¹¹ For instance, when sodium reacts with chlorine gas, sodium chloride is formed:

2Na + Cl₂ -> 2NaCl

The reaction is highly exothermic and can release a significant amount of energy. Alkali metals readily donate their outermost electron to halogens, forming stable ionic compounds.

These examples demonstrate the higher reactivity of alkali metals, showcasing their tendency to readily lose electrons and form compounds with other elements. Their reactivity makes them useful in various applications but also requires careful handling due to potential hazards.

Further reading

Why are Noble Gases Unreactive?
Is Ice a Mineral?
Is Granite a Mineral?
Is Amber a Mineral?
Is Lithium a Mineral?

1. Group 1: Reactivity of Alkali Metals. (2017, September 19). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Group/Group_01%3A_Hydrogen_and_the_Alkali_Metals/2Group_1%3A_Reactivity_of_Alkali_Metals
2. Boudreaux, K. A. (n.d.). The Parts of the Periodic Table. The Parts of the Periodic Table. https://www.angelo.edu/faculty/kboudrea/periodic/periodic_main1.htm
3. Ionization Energy. (2013, October 2). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Ionization_Energy
4. Alkali metal – Wikipedia. (2012, March 24). Alkali Metal – Wikipedia. https://en.wikipedia.org/wiki/Alkali_metal
5. Gsu.edu https://hyperphysics.phy-astr.gsu.edu/hbase/pertab/alkmet.html
6. Information on Alkali Metals – Stanford Environmental Health & Safety. (n.d.). Information on Alkali Metals – Stanford Environmental Health & Safety. https://ehs.stanford.edu/reference/information-alkali-metals
7. Le.ac.uk https://journals.le.ac.uk/ojs1/index.php/pst/article/download/4246/3618
8. Reactions of alkali metals with water – Group 1 alkali metals – GCSE Chemistry (Single Science) Revision – WJEC – BBC Bitesize. (n.d.). BBC Bitesize. https://www.bbc.co.uk/bitesize/guides/zdykw6f/revision/2
9. Activity Series – Alkali Metals in Water | Department of Chemistry | University of Washington. (n.d.). Activity Series – Alkali Metals in Water | Department of Chemistry | University of Washington. https://chem.washington.edu/lecture-demos/activity-series-alkali-metals-water
10. Reactions of alkali metals with oxygen – Group 1 alkali metals – GCSE Chemistry (Single Science) Revision – WJEC – BBC Bitesize. (n.d.). BBC Bitesize. https://www.bbc.co.uk/bitesize/guides/zdykw6f/revision/3
11. Reactions of alkali metals with halogens – Group 1 alkali metals – GCSE Chemistry (Single Science) Revision – WJEC – BBC Bitesize. (n.d.). BBC Bitesize. https://www.bbc.co.uk/bitesize/guides/zdykw6f/revision/4