Why alkali metals are strong reducing agents

Why alkali metals are strong reducing agents?

Alkali metals are strong reducing agents because they can release their valence electrons very easily. When consider about first ionization enthalpy in a period, alkali metals has the lowest values.

All alkali metals easily remove its last shell electron to make +1 ion.

Electrochemistry series

This strong reducing behaviour 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 earth metals

Alkali earth metals exist as compounds because they are very reactive. They combine with other elements to form compounds. Alkali earth metals do not exist as free elements.

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 hydroxides.

Reducing ability along the group

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

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.

Alkali metals reduces following compounds

  • Water - Hydrogen in the water reduces and H2 gas forms. Alkali metal oxidized.
  • Acids - H2 gas and alkali metal salt are given.
  • Halogens - Halogen is reduced. Alkali metal halide is given.
  • Sulfur - Metal sulfides are given.
  • Oxygen - Metal oxide is given.
  • Ammonia - Matal 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

Why reducing ability increases along 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 decreses. Then ability of releasing that electron increses when going down the group. That increases the reducing ability.

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