Chemical Properties of Alkali Metals

What are the Chemical Properties of Alkali Metals?

The chemical properties of alkali metals can be described as the greatest electropositive characteristics of all elements. This means they react with a wide range of non-metals. Lithium’s chemical reactivity is more similar to Group 2 (IIa) metals than the other metals in its group. Alkali metals react with carbon, nitrogen, and hydrogen more than other alkali metals.

Alkali metals have the following chemical and physical properties:

• High reactivity at standard pressure and temperature
• Quickly lose an electron to form +1 cations
• Shiny
• Silvery
• Soft

They are soft, making them easy to cut with a plastic knife. Their bright surface tarnishes rapidly in the air. Alkali metals are very reactive and must be kept under oil to avoid air reaction. All Group 1 elements, excluding hydrogen, according to the IUPAC display these characteristics. Heavy alkali metals react more violently with water than light.

Reactions with Oxygen

Alkali metals tend to produce ionic solids with oxidation number +1. Thus, neutral oxygen compounds may easily characterise the oxygen species. The ionic oxygen species are oxide, peroxide, superoxide, and ozonide. The alkali metal M and oxygen compounds are M2O2, superoxide, MO2, monoxide, M2O, peroxide, and ozonide, MO3. Rubidium, cesium, and maybe potassium creates M4O6, a sesquioxide with two peroxide anions, and one superoxide anion and lithium only produces monoxide and peroxide.

4M(s) + O2(g)→ 2M2O

4Li + O2→ 2Li2O

2Na + O2→Na2O

All alkali metals react directly with oxygen, forming monoxides (Li2O and Na2O) and superoxides (MO2). The reaction rate with oxygen or air relies on the metal’s state (solid or liquid) and the degree of mixing with oxygen or air. If ignited in the liquid form, alkali metals produce huge quantities of heat and oxide smoke.

The free energy of the formation of alkali metal oxides ranges from 133 kcal/mole for lithium oxide to 63 kcal/mole for caesium oxide at 25 °C (77 °F), with the lithium oxide having an extremely high free energy of formation due to the tiny lithium ions near the oxygen atom. Passing oxygen through an alkali metal liquid-ammonia solution forms the peroxides (Li2O2 and Na2O2). However, the oxidation of sodium monoxide produces sodium peroxide commercially. 

High oxygen pressures may produce sodium superoxide (NaO2), whereas burning in air produces rubidium, potassium, and cesium superoxides. 

M + O2(g)→ MO2  where M is K/Rb/Ce

On the other hand, lithium and alkaline-earth metals contain no pure superoxides, though they may oxidise to peroxide their heavier components. The reaction of superoxides with ozone produces potassium, rubidium, and caesium cyanides, which are less stable than lower oxides.

Reactions with Water

All alkali metals react violently with water, according to M + H2O →MOH + 1/2 H2. The rate of reaction relies on the metal surface exposed to the liquid. Small metal droplets or alkali metal thin films can be explosive. The rate of water reaction with alkali metals rises with metal atomic weight. 

Heavier alkali metals easily remove less soluble hydroxides from the reactive surface, continuing the reaction unabated. When we mix alkali metal and water equimolarity, they produce alkali metal hydroxide and half a mole of hydrogen gas. The produced hydrogen may react with oxygen to increase the heat generated.

Reactions with Non-metals

Only lithium and nitrogen react to form nitride (Li3N), making it more similar to alkaline-earth metals than Group 1 metals. Lithium also produces a stable hydride, while other alkali metals create reactive hydrides. Lithium, like calcium, produces a carbide (Li2C2). Although they react with graphite, they do not form stable carbides to generate intercalation compounds.

It is possible to burn alkali metals to generate halides by mixing them with various halogens. Exothermic reactions produce up to 235 kcal/mole lithium fluoride. Group 15 and 16 (Va and VIa) alkali metals react with non-metals. The direct reaction of alkali metals with sulphur produces a range of sulphides. Phosphorus combines with alkali metals to generate phosphides with the general formula M3P.

Formation of Alloys

There is a similarity in the components involved in the alloy used to assess alloy behaviour in alkali metals. Some dissimilarity in atomic volume results in eutectic-type systems, while greater dissimilarity results in wholly immiscible systems. Rubidium, potassium, and cesium undergo a high-pressure transition from s-type to d-type metals, producing atomic volumes similar to multiple transition metals at the same pressure. It enables alkali metals to create alloys with transition metals like nickel or iron.

Compared to sodium, potassium, rubidium, and caesium tend to form eutectic systems with similar atomic volumes and ionisation energies. Sodium and lithium have very different atomic volumes, causing liquid phase in solubilities. From the lithium-sodium alloy to lithium-cesium alloy, the consolute temperature increases. At temperatures over 1,100 °C (2,000 °F), lithium and caesium may coexist as two separate liquid phases.

The lithium-magnesium system is a unique example of solid miscibility in alkaline-earth-metal binaries. Only barium and sodium form alkaline-earth metal compounds, and the heavier alkali metals tend to mix with them.

Zinc, cadmium, and mercury (Group 12 (IIb)) react with alkali metals to create compounds. Except for the amalgam with lithium (MHg2), mercury produces six amalgams with each of the five alkali metals. Lithium and sodium combine with cadmium and zinc to produce compounds.

The Importance of Chemical Properties of Alkali Metals 

The chemical properties of alkali metals’ importance is presented in the following points:

• Higher temperatures cause alkali metals to produce metallic hydrides. Metallic hydrides release ions.
• Alkali metals may generate nitrides when they react with even atmospheric nitrogen.
• Alkali metals react with atmospheric oxygen, lose their shine, and oxidise with oxygen. But the oxides generated have a different nature.
• The reaction of alkali metal and water generate basic hydroxides that release hydrogen. The metal reaction is exothermic and increases in enthalpy from lithium to cesium.

Conclusion

Alkali refers to the metal hydroxides’ basic or alkaline nature. Because they form alkalies, which are strong bases capable of neutralising acids when they react with water, the compounds are alkali metals.

Noble gas-like alkali metals have an ns1 electronic configuration. They are in the periodic table’s first column. Sodium (Na), Cesium (Cs), Rubidium (Ru), Potassium (K), Lithium (Li), and Francium (Fr) are alkali elements that occupy successive periods from first to seventh, and the radioactive element francium has a short life.

Hydrogen is not an alkali metal. It is a gas at normal pressure and temperature, and high pressure causes hydrogen to change properties or become an alkali metal.