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Alkali metals are the first group of s-block elements that are found on the leftmost side of the periodic table. Alkali metals are the most electropositive elements on the periodic table as they easily lose electrons. These metals formed various useful compounds with halides, oxygen, and sulfur. Alkali metals form a strong base in their aqueous solution.

In this article, we will learn about, alkali metals, their electronic configuration, periodic trends, physical and chemical properties, and others in detail.

Alkali Metals Definition

We define alkali metals as the member of s-block of the periodic table and these are the members of the first group of the table. They are called alkali metals because their aqueous solution forms a strong alkaline (basic) solution. These metals on dissolving in water easily release their electrons and form positive ions (cations). They are the most electropositive elements in the periodic table. They are one of the most reactive elements in the periodic table.

Alkali Metal Examples

The various alkali metals are,

  • Lithium(Li)
  • Sodium(Na)
  • Potassium (K)
  • Rubidium (Ru)
  • Cesium (Cs)
  • Francium (Fr)

Even though Hydrogen is placed with the Alkali metal group it is not considered to be an alkali metal.

Why Hydrogen is not an Alkali Metal?

The position of Hydrogen is in the Alkali Group but Hydrogen is not considered to be a true alkali even though it has some properties of Alkali as it is mostly found in gaseous and some of its properties are similar to Halogens.

Position of Alkali Metal in Periodic Table

The alkali metals in the periodic table are placed at the right corner in the periodic table. They are placed in the first column of the periodic table. The image added below shows the position of alkali metals in the periodic table.

Alkali Metals

 

Alkali Metals Overview

The table added below tells us in brief about the properties of Alkali Metals

Metals

Lithium

Sodium

Potassium

Rubidium

Cesium

Atomic number311193755
SymbolLiNaKRbCs
Configuration[He]2s1[Ne]3s1[Ar]4s1[Kr]5s1[Xe]6s1
Abundance (ppm)6528300259003107
Reduction potential (v)-3.04-2.714-2.925-2.93-2.927
Ionization energy kJ/mol520496419403376
Hydration enthalpy kJ/mol-506-406-330-310-276
Flame colorCrimson redYellowVioletRed violetBlue
Density g/cm30.530.970.861.531.9
Atomic size (pm)152186227248265

Electronic Configuration of Alkali Metals

Alkali Metals are the metal that is placed in the first group of the periodic table. They have one electron in their outermost shell. 

The general electronic configuration of alkali metals is ns1. For example, the electronic configuration of Lithium is 1s2, 2s1. They easily lose this electron in the outermost shell to form positive ions. They have a charge of +1.

The ionic configuration of all the elements of the Alkali metal is discussed below,

Alkali MetalSymbolElectronic Configuration
LithiumLi[He]2s1
SodiumNa[Ne]3s1
PotassiumK[Ar]4s1
RubidiumRb[Kr]5s1
CesiumCs[Xe]6s1

Francium (Fr) is also an Alkali metal but its general electronic configuration is not given because it is a Radioactive Element.

Trends in Physical Properties of Alkali Metals

The physical properties of alkali Metals follow a general trend while moving down the group in the periodic table. We learn about various trends of alkali metal that include,

  • Atomic and Ionic Radii of Elements
  • Density of Alkali Metals
  • Electropositive Metallic Character
  • Ionization Energy
  • Solubility or Hydration of Alkali Metal Ions
  • Reduction Potential
  • Flame Coloration

Now, let’s learn about these properties in detail and follow their trend.

Atomic and Ionic Radii of Elements

The atomic radii and ionic radii of alkali metals increase in a straight line down the column. Furthermore, in the corresponding period, every alkali metal has the largest radii of any element.

  • Order of Atomic Radius: Li ˂ Na ˂ K ˂ Rb ˂ Cs
  • Order of Ionic Radius: Li+ ˂ Na+ ˂ K+ ˂ Rb+ ˂ Cs+

Density of Alkali Metals

Alkali elements have the lowest density because they have the largest radius and volume. As a result of low density, they are extremely soft and can be cut with a knife. The elements Lithium, Sodium, and Potassium are all lighter than water. Among all the alkali metals, Potassium(K) has the lowest density.

Electropositive Metallic Character

Alkali metals are electropositive metals that easily form cations by releasing their only electrons of the valance shell. Lithium is the most electropositive metal that is present in the periodic table.

Ionization Energy

Ionization energy of the alkali metal decreases as we go down along the group in the periodic table. The smaller Lithium atom requires the highest ionization energy to remove the valence electron. Increasing the atomic size of the alkali metals lowers the electrostatic pull of the nucleus to the electrons making it easier for the electron to escape from its valance shell.

As a result, with the increase in the atomic number increases ionization energy decreases.

Decreasing Order of Ionization Energy: Li > Na > K > Rb > Cs

Solubility  of Alkali Metal Ions

The most soluble alkali metal ion is the Lithium-ion, and as the size of the ion increases, the solubility of the alkali metal ion decreases, with the Cesium ion being the least water-soluble alkali metal ion. The ionic nature and size of a substance influence its solubility in water. Smaller ions have a higher charge density and can be dissolved by more water molecules. This results in a higher enthalpy of hydration and more stable hydrated ions.

Solubility of Alkali Metal: Li+ > Na+ > K+ > Rb+ > Cs+

Reduction Potential

Reducing agents are substances that easily donate their electrons and form positive ions. As Alkali Metals easily donate their electrons and form positive ions they are considered to be good reducing agents. The reduction potential of the elements is inversely proportional to the ionization energy of the elements as the ionization energy decreases reduction potential increases.

As we know in the case of Alkali metal the ionization energy decreases along the period so the reduction potential increases.

The reduction potential of the Alkali metals follows the trends,

ENa ˂ EK ˂ ERb ˂ ECs

Flame Coloration

The energy required for an electronic transition between available energy levels in s-block elements falls in the visible spectrum region. As a result, when heated, they have a distinct flame color.

Chemical Properties of Alkali Metals

Various chemical properties of alkali metals are discussed below,

Hydrides

At higher temperatures, alkali metals react with hydrogen to form metallic hydrides. Hydride ions are released by metallic hydrides.

2M + H2 → 2MH → M+ + H

Nitrides

Nitrides can be formed when alkali metals react with even atmospheric nitrogen.

6M + N2 → 2M3N

Oxides

Alkali metals tarnish their gleaming nature when they react with atmospheric oxygen. Oxides are formed when they react with oxygen. However, the nature of the oxides formed differs. They each have a different oxidation state for oxygen. Smaller lithium atoms form a normal oxide, while sodium atoms form peroxides and larger atoms form superoxides. Because alkali metals react in the air with nitrogen, oxygen, and water, they are always stored in kerosene.

  • 4Li + O2 → 2Li2O (Here the compound form is called Oxides)
  • 2Na + O2 → Na2O2 (Here the compound form is called Peroxide)
  • Cs + O2 → Cs2O (Here the compound form is called Superoxide)

Hydroxides of Alkali Metals

Reaction of water and alkali metal yields hydroxide of metal and liberated the hydrogen. We can represent this as,

2M + 2H2O → 2M+ + 2OH + H2 + ∆H

Some examples of the reaction of metal with water resulting in the formation of metal hydroxides are,

  • 2Na + 2H2O → 2Na+ + 2OH + H2 + ∆H
  • 2Li + 2H2O → 2Li+ + 2OH + H2 + ∆H
  • 2K + 2H2O → 2K+ + 2OH + H2 + ∆H

Oxides and Water

The oxides of the alkali metals react with the water to form the alkali metal hydroxide, this reaction is represented as,

M2O + H2O → 2MOH

Some examples of the reaction of alkali metal oxide with water resulting in the formation of metal hydroxides are,

  • Li2O + H2O → 2LiOH
  • Na2O2 + 2H2O → 2NaOH + H2O2
  • 2KO2 + 2H2O → 2KOH + H2O2 + O2

Carbonates and Bicarbonates

The hydroxides of the alkali metals react with carbon dioxide to form metal carbonate. The reaction of sodium hydroxide with carbon dioxide forming sodium carbonate is discussed below,

2NaOH + CO2 → Na2CO3 + H2O

Halides

All alkali metals react violently with the halides, and the reactivity of the halides decreases from Fluorine to Iodine. The reaction of heavy alkali metals with halide forms poly halides by combining more halogens. The reaction of potassium iodide with iodine is described as,

KI + I2 → KI3

Reaction of Alkali Metals with Liquid Ammonia

Alkali metals easily react with liquid ammonia to form Sodamide and liberate the hydrogen gas.

M + (x + y)NH3 → [M(NH3)x]+ + [M(NH3)y] → MNH2 + ½H2

Extraction of Alkali Metals

The conventional extraction method is inapplicable to the extraction of alkali metals. Since these metals have the highest electropositivity, displacement, and electrolysis are not applicable. Furthermore, high electrode potential limits the ability to reduce agents such as carbon to reduce them. 

Hydrogen ions are preferentially reduced to gaseous hydrogen during aqueous solution electrolysis over sodium ions. As a result, sodium and potassium can only be obtained by electrolysis of the fused salts of sodium hydroxide and sodium chloride. Alkali metals combine to form alloys, and amalgams with other metals.

Anomalous Behaviour of Lithium

Because of its small size, high ionization energy, and strongest electropositive and polarizing properties, lithium differs from other alkali metals in that it has a more covalent nature. Because of its small size, higher solubility, and highest electrode potential, lithium has the strongest reducing character.

Learn more about, Anomalous Behavior of Lithium

Diagonal Relationship of Lithium with Magnesium

Lithium and Magnesium have a diagonal relation, i.e. they have similar properties and their position is diagonal in the periodic table. Some of the similar properties of Lithium and Magnesium are,

  • Lithium from the alkali metal group is more similar to magnesium from the alkaline earth metal group.
  • Magnesium and lithium are harder metals with higher melting points.
  • Both slowly react with water, releasing hydrogen.
  • Water hydrolyzes both nitrides, releasing ammonia.
  • Both produce normal oxides, which are less water-soluble.
  • Both produce carbide, which when hydrolyzed yields acetylene.
  • Lithium and magnesium bicarbonates are only stable in solution and not in solid form.

Uses of Alkali Metals

Various uses of Alkali metals are,

  • Lithium, sodium, and potassium have numerous applications, whereas rubidium and cesium are particularly useful in academic settings.
  • Lithium is commonly used in lithium-ion batteries, and lithium oxide can aid in the processing of silica.
  • Lithium chloride is a brazing alloy used for aluminum parts.
  • Metallic lithium is combined with magnesium and aluminum to create extremely tough and light alloys.
  • Sodium chloride, which is used as table salt.
  • Soap is made from sodium salts of fatty acids.
  • Pure sodium metal has numerous applications, including use in sodium-vapor lamps, which produce very efficient light compared to other types of lighting and can aid in the smoothing of other metals’ surfaces.
  • Potassium compounds are frequently used as fertilizers because potassium is an essential nutrient for plants.
  • Potassium hydroxide is a very strong base that is used to regulate the pH of a variety of substances.

Read More,

FAQs on Alkali Metals

Q1: What are Alkali Metals?

Answer:

The alkali metals are the metal of the s-block of the periodic table that have one electron in their outermost shell.

Q2: Which Alkali Metal is the Strongest Reducing Agent?

Answer:

The alkali metal Lithium is the strongest reducing agent.

Q3: Why Alkali Metals are Good Reducing Agents?

Answer:

Alkali metals are a good reducing angle because they easily lose their valance electrons and form cations.

Q4: How many Alkali Metals are there?

Answer:

There are six alkali metals that are,

  • Lithium(Li)
  • Sodium(Na)
  • Potassium (K)
  • Rubidium (Ru)
  • Cesium (Cs)
  • Francium (Fr)

Q5: Which Alkali Metal is Radioactive?

Answer:

The radioactive element that is radioactive in nature is Francium.

Q6: Why Alkali metals are the most Electropositive elements?

Answer:

Alkali metals are the most electropositive metals due to the fact that they easily lose electrons in the outermost shell. and form positive ions, such as M+.

Q7: Why is the Melting and Boiling Point of Alkali Metals low?

Answer:

Since alkali metals have only one valence electron, they have a weak metallic bonding. that is the cause of the low melting and boiling point of Alkali metal.

Q8: Why is Sodium kept under Kerosene Oil?

Answer:

As Sodium is the most reactive element, it easily reacts with the water present in the air. So it is placed in the Kerosene Oil to avoid its reaction with air.

Q9. Why is Lithium kept in Paraffin Wax?

Answer:

Since Lithium has the lowest density it floats on kerosene hence they are kept under paraffin wax to avoid reaction with air.



Last Updated : 19 Dec, 2023
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