Why are Group 1 elements called alkali metals?

The term 'alkali' originates from the Arabic word 'al-qali', meaning 'ashes'. Historically, the ashes of plants, which are rich in compounds of sodium and potassium, were found to produce strong basic (alkaline) solutions when dissolved in water. Similarly, when Group 1 metals react with water, they form strong bases (metal hydroxides) and hydrogen gas. For example, $2Na(s) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2(g)$. This characteristic property of forming strong alkaline solutions led to their classification as alkali metals.

Why do alkali metals have low ionization enthalpies?

Alkali metals possess very low first ionization enthalpies because they have only one electron in their outermost s-orbital, which is relatively far from the nucleus and effectively shielded by inner core electrons. This single valence electron is loosely held, making it easy to remove. As you move down the group, the atomic size increases, and the shielding effect becomes more pronounced, further reducing the effective nuclear charge experienced by the valence electron, thus decreasing the ionization enthalpy.

Why does lithium show anomalous behavior compared to other alkali metals?

Lithium's anomalous behavior stems primarily from its exceptionally small atomic and ionic size, and consequently, its very high charge-to-radius ratio (polarizing power). It also has a relatively high ionization enthalpy and electronegativity for an alkali metal, and lacks d-orbitals in its valence shell. These factors lead to stronger covalent character in its compounds and distinct properties like forming a nitride, reacting less vigorously with water, and forming hydrated salts, differentiating it from heavier alkali metals.

Explain the phenomenon of flame coloration by alkali metals.

When alkali metals or their salts are introduced into a hot flame, the thermal energy excites their loosely held outermost s-electron to higher energy levels. This excited state is unstable, and the electron quickly falls back to its original ground state. During this transition, the excess energy is emitted as light. Since the energy difference between the excited and ground states is unique for each alkali metal, they emit light of specific wavelengths, which we perceive as characteristic colors in the visible spectrum (e.g., lithium: crimson red, sodium: golden yellow, potassium: lilac).

Why are alkali metals stored under kerosene oil?

Alkali metals are highly reactive due to their strong electropositive nature and low ionization enthalpies. They readily react with oxygen and moisture present in the air. For instance, they tarnish quickly by forming oxides and hydroxides. To prevent these vigorous reactions and preserve their metallic luster and reactivity, they are typically stored immersed in inert liquids like kerosene oil. Lithium, being less dense, is often stored in paraffin wax or wrapped in paraffin paper.

Why is $Li^+$ the strongest reducing agent in aqueous solution, despite having the highest ionization enthalpy among alkali metals?

While $Li$ has the highest ionization enthalpy (meaning it's hardest to remove an electron in the gaseous state), its reducing power in aqueous solution is determined by the overall energy change involving three steps: atomization, ionization, and hydration. $Li^+$ ion, due to its extremely small size, has an exceptionally high hydration enthalpy. This large amount of energy released during hydration more than compensates for its high ionization enthalpy, making the overall process of forming hydrated $Li^+$ ions highly favorable. Thus, $Li$ readily loses an electron and becomes the strongest reducing agent in aqueous solution.

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Group 2 Elements: Alkaline Earth Metals

Group 1 Elements: Alkali Metals

Chemistry

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Version 1Updated 22 Mar 2026

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Group 1 elements, commonly known as alkali metals, comprise Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), and Francium (Fr). Positioned in the s-block of the periodic table, they are characterized by having one valence electron in their outermost s-orbital, leading to a strong tendency to lose this electron and form a unipositive ion ( $M^+$ ). This electron configuration di…

Quick Summary

Group 1 elements, known as alkali metals (Li, Na, K, Rb, Cs, Fr), are highly reactive metals located in the s-block of the periodic table. They all possess a single valence electron ( $ns^1$ ) which they readily lose to form unipositive ions ( $M^+$ ), achieving a stable noble gas configuration.

This leads to their low ionization enthalpies and strong electropositive character. Key properties include large atomic radii, low densities (with K being an exception), low melting/boiling points, and characteristic flame colors (Li-crimson, Na-golden yellow, K-lilac).

Reactivity increases down the group. They react vigorously with air and water, forming oxides/hydroxides and releasing hydrogen. Lithium exhibits anomalous behavior due to its small size and high polarizing power, showing similarities with magnesium (diagonal relationship).

They are crucial in various applications, from batteries to photoelectric cells.

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Key Concepts

Trends in Ionization Enthalpy

Ionization enthalpy is a critical property dictating reactivity. For alkali metals, the first ionization…

Reactivity with Water

Alkali metals react vigorously with water to produce metal hydroxides and hydrogen gas, represented by the…

Anomalous Properties of Lithium

Lithium, the first member of Group 1, deviates significantly from the typical behavior of other alkali…

General electronic configuration:

[Noble\,gas]ns^1

Oxidation state: +1

Atomic/Ionic Radii: Increase down group

Ionization Enthalpy: Decreases down group (very low)

Hydration Enthalpy: Decreases down group (

Li^+ > Na^+ > K^+ > Rb^+ > Cs^+

)

Density: Increases down group (K < Na exception)

Melting/Boiling Points: Decrease down group (weak metallic bonding)

Reactivity: Increases down group

Flame colors: Li - Crimson, Na - Golden Yellow, K - Lilac, Rb - Red-violet, Cs - Blue

Li anomalous properties: Smallest, highest IE, highest hydration enthalpy, forms

Li_3N

, forms

Li_2O

, hydrated salts, strongest reducing agent in aqueous solution, diagonal relationship with Mg.

Reactions with

O_2

Li \rightarrow Li_2O

Na \rightarrow Na_2O_2

K, Rb, Cs \rightarrow MO_2

Reactions with

H_2O

2M + 2H_2O \rightarrow 2MOH + H_2

(vigor increases down group)

Reactions with

NH_3(l)

: Deep blue solution (ammoniated electrons), paramagnetic, forms amides on standing.

For Flame Colors: Little Crimson Naked Gorillas Kiss Lilacs. (Li-Crimson, Na-Golden, K-Lilac)

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