Why Alkali Metals are Strong Reducing Agents than Other Metals

Alkali metals are strong reducing agents because they can readily release their valence electron (All alkali metals easily remove its last shell electron to make +1 cation). When consider about first ionization enthalpy in a period, alkali metals has the lowest values. In this tutorial, we will discuss why alkali metals (group IA metals) become strong reducing agents compared to other metals.

Content

Reactions to prove why alkaline earth metals are more strong reducing agents than other metals
- Reactions with water
- Reactions with air and oxygen gas
- Alkali metals reduces following compounds
Electrochemistry series to explain why alkaline metals show higher reducing capabilities
Occurrence of alkali metals in the nature
- Hydrogen and other alkali metals
Reducing ability along the group
- Why reducing ability of alkali metals increases going down the group?
- How do you prove alkali metals are very good reducing agents?

Reactions to prove why alkaline earth metals are more strong reducing agents than other metals

Let's consider Sodium, Magnesium and Aluminium to compare with each other. All these three metals belong to the 3^rd period of the periodic table.

Reactions with water

We know usually metals prefer to react with water and eliminate hydrogen gas and metal is oxidized.
Experimentally, we know that both Magnesium and Aluminium do not react with cold water. But, Sodium aggressively react with water to eliminate hydrogen gas and produce Sodium hydroxide. It proves that Sodium has more reducing capabilities than Magnesium and Aluminium

reaction of sodium magnesium aluminium with water

Reactions with air and oxygen gas

As with water, We know usually metals react with oxygen gas when that metal is exposed to ambient air and give metal oxide as the result.
Both Magnesium and Aluminium react with oxygen gas when exposed to air. But, those two metals take some time to give their respective oxide.
But, Sodium reacts more quickly with oxygen gas and you can see solid sodium metal piece turns to grayish white upon exposure to air.

Alkali metals reduces following compounds

Water - Hydrogen in the water reduces and Hydrogen gas is formed. Alkali metal oxidized and alkali metal hydroxide is given.
Acids - Hydrogen gas and alkali metal salt are given.
Halogens - Halogen is reduced to halide anions. Alkali metal halide is given as the product.
Sulfur - Metal sulfides are given.
Oxygen - Metal oxide is given.
Ammonia - Alkali metal Azanide and hydrogen gas are produced. Example : NaNH₂ and H₂
Hydrogen sulfide - Metal sulfide and hydrogen gas are given as products.
Phosphorous - Alkali metals forms metal phosphide. Examples: Na₃P

Electrochemistry series to explain why alkaline metals show higher reducing capabilities

This strong reducing behavior of alkali metals is also indicated by their very large negative values of reduction potentials in electrochemistry series. Lithium has the highest negative reduction potential value in the electrochemistry series.

Occurrence of alkali metals in the nature

Alkali metals exist as compounds in the nature because they are very reactive. They combine with other elements to form compounds. As alkali metals do not exist as free elements like Gold.

Hydrogen and other alkali metals

All of alkali metals are better reducing agents than hydrogen. Therefore alkali metals can liberate H₂ by reacting with compounds which include acidic hydrogen atoms such as HCl, H₂SO₄, alcohols, acetylene. Also alkali metals can liberate H₂ from water by forming strong aqueous hydroxide solutions.

Reducing ability along the group

Reducing ability increases along the group. It means that, reducing ability of potassium is higher than sodium.

Why reducing ability of alkali metals increases going down the group?

Atomic radius of alkali metals increases when going down the group. Therefore attraction of only electron in the last shell towards the nucleus decreases. Then ability of releasing that electron increases when going down the group. That increases the reducing ability.

How do you prove alkali metals are very good reducing agents?

See the electro-chemistry series and look its top elements. You can see in the top, there are lithium, potassium and sodium as alkali metals.

Questions

Why are alkali metals strong reducing agents than d block metals

Reducing agents means that those compounds are oxidized while other compounds are reduced. In this kind of reaction, electrons are exchanged are among compounds.
Metals prefer to eliminate electrons to form cations. Some metals such as alkali metals readily eliminate electrons compared to d block metals because electrons in outer shells of alkaline metals are poorly attracted towards the nucleus.
Due to that, alkali metals (group 1) become strong reducing agents than d block metals.

why group 1 metals become strong reducing agents than group 2 metals?

Electrons in the outer shells of group 2 metals are strongly attracted towards the nucleus compared to group 1 metals. Therefore, releasing outer shells electrons is much more difficult for group 2 metals. Therefore, reducing power of group 2 metals is much weaker than group 1 metals.