Alkali Metals

The fascinating family of the s- s-block elements in Group 1 of the Periodic Table are known as Alkali metals. These elements are well-known for having unique chemical and physical characteristics as well as strong reactivity in the Periodic Table

The essential components of alkali metals, such as their location in the Periodic Table and general properties, will be discussed in this article. They are essential to many scientific and industrial applications.

In this article, we will cover the topic of Alkali metals. This topic falls under the broader category of (The s - Block elements) which is a crucial chapter in (Class 11 Chemistry)

The General Characteristics of Alkali Metals are as follows:

Electron Configuration:

Alkali metals have an electron configuration of ns¹, where n is the period number.

Physical characteristics such as:

• Softness: These metals are easily cut with a knife due to their softness.
• Low Density: Lithium, sodium, and potassium have lower densities than water, making them less dense than the majority of metals.
• Shiny Appearance: They show metallic brilliance when they are freshly cut.
• Low Melting and Boiling values: As you move down the group, their melting and boiling values get gradually lower.
• Physical Properties of Alkali Metals :
• All the alkali metals are silvery-white, soft and light metals.
• Because of the large size, these elements have low density which increases down the group from Li to Cs. However, potassium is lighter than sodium.
• The melting and boiling points of the alkali metals are low indicating weak metallic bonding due to the presence of only a single valence electron in them.
• The alkali metals and their salts impart characteristic colour to an oxidizing flame. This is because the heat from the flame excites the outermost orbital electron to a higher energy level. When the excited electron comes back to the ground state, there is the emission of radiation in the visible region of the spectrum as given below:
• The other physical properties of Alkali metals are:

Physical properties of Alkali Metals- 2 :

Melting and Boiling Point

• The melting and boiling points of these metals are quite low.
• Melting point and Boiling point decrease down the group.
• This is because the metallic bonding becomes weak as we move down the group.
• The weak metallic bonding can be attributed to the involvement of a single electron in the bonding.

Oxidation state

• All the alkali metals show an oxidation state of +1
• This is because, upon loss of one electron, these attain stable noble gas configuration.
• All the alkali metal ions are diamagnetic in nature with no unpaired electrons

Chemical characteristics such as:

• High Reactivity: They react very quickly, particularly to oxygen and water. Down the group, reactivity rises.
• Formation of Hydroxides: When they react with water, they produce hydrogen gas and hydroxides, such as NaOH.
• Ionic Compound Formation: To create +1 cations and ionic compounds, they easily give up their single valence electron.

Chemical Properties of Alkali Metals: Alkali metals are highly reactive due to their large size and low ionization enthalpy. The reactivity of these metals increases down the group.

• Reactivity towards air: The alkali metals tarnish in dry air due to the formation of their oxides which in turn react with
  moisture to form hydroxides. They burn vigorously in oxygen forming oxides.
• Reactivity towards water: The alkali metals react with water to form hydroxide and dihydrogen.2M+2H2O→2M++2OH−+H2
• Reactivity towards dihydrogen: The alkali metals react with dihydrogen at about 673K (lithium at 1073K) to form hydrides. All the alkali metal hydrides are ionic solids with high melting points.
• Reactivity towards halogens: The alkali metals readily react vigorously with halogens to form ionic halides, M⁺X^-.
  However, lithium halides are somewhat covalent.
• Reducing nature: The alkali metals are strong reducing agents, lithium being the most and sodium the least powerful

Chemical Properties of Alkali Metals - 2 :

Carbonates and Bicarbonates

• The carbonates of the alkali metals are stable to heating except Li₂CO₃
• Li₂CO₃ dissociates upon heating to form its oxide and liberates CO₂ gas

Li₂CO₃→ΔLi₂O+CO₂

• Thermal stability of the alkali metal carbonates increase down the group. This is because of Lattice energy effects in which larger anions are more stabilised by larger cations and vice versa.
• The bicarbonates of the alkali metals are also quite stable and exist in the solid state except Lithium bicarbonate
• The bicarbonates (except Li) however dissociate upon heating to give the respective carbonate and release

2MHCO₃→ΔM₂CO₃+CO₂+H₂O

• Lithium bicarbonate does not exist in the solid state and is unstable.

Solutions of Alkali Metals in Liquid Ammonia

• The alkali metals dissolve in liquid ammonia giving deep blue solutions which are conducting in nature.
• These solutions are also reducing in nature
• The blue colour of the solution is due to the ammoniated electron which absorbs energy in the visible region of light and thus imparts blue colour to the solution.
• These solutions are paramagnetic
• Upon increasing the concentration, the electrons start to pair up and the paramagnetism decreases
• The colour of the solution also changes to Bronze upon increasing the concentration.

Recommended topic video on (Alkali Metals)

Some Solved Examples

Example 1

Question: Which one of the following benefaction processes is used for the mineral Al₂O₃⋅2H₂O?

1. Froth floatation
2. Leaching
3. Liquation
4. Magnetic separation

Solution:
Leaching is used to concentrate the ore. The powdered ore is treated with a suitable chemical reagent that dissolves the ore while the impurities remain insoluble. For example, bauxite is separated from Fe₂O₃, SiO₂, and TiO₂ with the help of NaOH, in which Al₂O₃ gets dissolved while the rest are insoluble. Hence, the correct answer is option 2.

2\Example 2

Question: Al₂O₃ was leached with alkali to get X. The solution of X on passing gas Y forms Z. X, Y, and Z respectively are:

1. X=Na[Al(OH)₄],Y=CO₂,Z=Al₂O₃⋅xH₂OX
2. X=Al(OH)₃,Y=SO₂,Z=Al₂O₃⋅xH₂O
3. X=Na[Al(OH)₄],Y=SO₂,Z=Al₂O₃
4. X=Al(OH)₃,Y=CO₂,Z=Al₂O₃

Solution:
Al₂O₃ is leached out as sodium aluminate (Na[Al(OH)₄]). The aluminate in the solution is neutralized by passing CO₂ gas, and hydrated Al₂O₃ is precipitated. Hence, X = Na[Al(OH)₄], Y = CO₂ , and Z = Al₂O₃⋅xH₂O . Therefore, the correct answer is option 1.

Example 3

Question:

Match List - I with List - II.

List - I:
(A) Concentration of gold ore
(B) Leaching of alumina
(C) Froth stabilizer
(D) Blister copper

List - II:
(I) Aniline
(II) NaOH
(III) SO₂
(IV) NaCN

Choose the correct answer from the options given below:

1. (A)-(IV), (B)-(III), (C)-(II), (D)-(I)
2. (A)-(IV), (B)-(II), (C)-(I), (D)-(III)
3. (A)-(III), (B)-(II), (C)-(I), (D)-(IV)
4. (A)-(II), (B)-(IV), (C)-(III), (D)-(I)

Solution:
(A) NaCN is used for the concentration of gold ore. (IV)
(B) Leaching of alumina is done by NaOH (II)
(C) Froth stabilizer is aniline (I)
(D) Blister copper is due to the evolution of SO₂ (III)

Hence, the correct answer is option 2.