Alkali Metals: Definition, Properties, Facts and Examples

Alkali Metals

Edited By Shivani Poonia | Updated on Jul 02, 2025 06:32 PM IST

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

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.

Example 1

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

Froth floatation
Leaching
Liquation
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 TiO₂with 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:

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

(A)-(IV), (B)-(III), (C)-(II), (D)-(I)
(A)-(IV), (B)-(II), (C)-(I), (D)-(III)
(A)-(III), (B)-(II), (C)-(I), (D)-(IV)
(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.

Summary

Alkali metals are vital elements with distinctive characteristics and a variety of uses. Their behaviour and reactivity offer important insights into basic chemical principles and useful applications in a variety of industries. For their safe and efficient use, it is essential to fully understand their characteristics and safe handling procedures.

Alkali Metals

Frequently Asked Questions (FAQs)

1. Why are alkali metals so reactive?

Alkali metals are highly reactive due to their single valence electron in the outermost shell. This electron is easily lost, allowing the atom to achieve a stable electron configuration. The large atomic size and low ionization energy also contribute to their high reactivity.

2. What is the trend in reactivity among alkali metals as we move down the group?

The reactivity of alkali metals increases as we move down the group. This is because the atomic size increases, making it easier for the outermost electron to be removed. Additionally, the ionization energy decreases down the group, further enhancing reactivity.

3. Why do alkali metals have low melting and boiling points compared to other metals?

Alkali metals have low melting and boiling points due to weak metallic bonding. Only one electron per atom participates in bonding, resulting in weaker inter-atomic forces compared to other metals with multiple valence electrons.

4. How do alkali metals react with water?

Alkali metals react vigorously with water, producing hydrogen gas and a metal hydroxide. The general reaction is: 2M + 2H2O → 2MOH + H2 (where M is the alkali metal). The reaction becomes more vigorous as we move down the group, with cesium reacting explosively.

5. Why are alkali metals stored in oil?

Alkali metals are stored in oil to prevent them from reacting with air and moisture. The oil acts as a barrier, protecting the highly reactive metals from oxidation and other unwanted reactions that would occur if exposed to the atmosphere.

6. What is the flame test, and how is it used to identify alkali metals?

The flame test is a qualitative analysis method used to detect the presence of certain elements, including alkali metals. When a sample containing an alkali metal is introduced to a flame, it produces a characteristic color. For example, lithium produces a red flame, sodium gives an intense yellow, and potassium produces a lilac color.

7. Why do alkali metals form ionic compounds?

Alkali metals form ionic compounds because they easily lose their single valence electron to achieve a stable electron configuration. This electron loss results in a positively charged ion (cation) that can form strong electrostatic bonds with negatively charged ions (anions) from other elements.

8. How does the atomic radius change as we move down the alkali metal group?

The atomic radius increases as we move down the alkali metal group. This is due to the addition of new electron shells with each period, which increases the distance between the nucleus and the outermost electrons. The effect of nuclear charge is diminished by the increased number of inner electron shells, leading to less effective attraction of outer electrons.

9. What is the relationship between alkali metals and alkali earth metals?

Alkali metals (Group 1) and alkali earth metals (Group 2) are both s-block elements. The main difference is that alkali metals have one valence electron, while alkali earth metals have two. This results in alkali metals being more reactive and forming +1 ions, whereas alkali earth metals form +2 ions and are generally less reactive.

10. Why do alkali metals have low ionization energies?

Alkali metals have low ionization energies because their single valence electron is relatively far from the nucleus and shielded by inner electron shells. This makes it easier to remove the outermost electron, requiring less energy compared to other elements.

11. How do alkali metals conduct electricity?

Alkali metals are excellent conductors of electricity due to their single valence electron, which is loosely held and can move freely within the metal structure. This "sea" of mobile electrons allows for the easy flow of electric current when a potential difference is applied.

12. Why are pure alkali metals soft enough to cut with a knife?

Pure alkali metals are soft because of their weak metallic bonding. With only one valence electron per atom contributing to the bonding, the inter-atomic forces are relatively weak. This allows the layers of atoms to slide past each other easily, resulting in a soft, malleable structure.

13. What is the diagonal relationship in chemistry, and how does it apply to lithium?

The diagonal relationship refers to similarities in properties between elements diagonally adjacent to each other in the periodic table. Lithium, the first alkali metal, shows some similarities to magnesium (an alkaline earth metal) due to their similar charge-to-size ratios. This relationship explains some of lithium's unique behaviors compared to other alkali metals.

14. How do alkali metals react with halogens?

Alkali metals react vigorously with halogens to form ionic halides. The reaction is highly exothermic, often accompanied by heat and light. The general reaction is: 2M + X2 → 2MX (where M is the alkali metal and X is the halogen). The resulting compounds are typically white, crystalline solids with high melting points.

15. Why do alkali metals form hydrides, and what are their properties?

Alkali metals form hydrides by directly combining with hydrogen gas. The resulting compounds (MH) are ionic and contain the hydride ion (H-). Alkali metal hydrides are strong reducing agents and react vigorously with water, producing hydrogen gas. They are used in organic synthesis and as drying agents.

16. How does the electronegativity of alkali metals compare to other elements?

Alkali metals have the lowest electronegativity values among all elements in the periodic table. This means they have a very low tendency to attract electrons in a chemical bond. Their low electronegativity contributes to their high reactivity and their tendency to form ionic compounds by losing electrons.

17. What is the anomalous behavior of lithium, and why does it occur?

Lithium exhibits some anomalous behavior compared to other alkali metals due to its small size and high charge density. This includes forming more covalent compounds, having a higher melting point, and being less reactive than expected. These properties are partly due to lithium's diagonal relationship with magnesium and its ability to polarize anions more effectively than other alkali metals.

18. How do alkali metals react with oxygen, and what products are formed?

Alkali metals react readily with oxygen to form oxides. However, the products vary depending on the metal and conditions. Lithium forms a normal oxide (Li2O), sodium forms a peroxide (Na2O2), and heavier alkali metals can form superoxides (MO2). These differences arise from the metals' ability to stabilize different oxygen anions.

19. Why do alkali metals have low first ionization energies but high second ionization energies?

Alkali metals have low first ionization energies because removing the single valence electron is relatively easy. However, the second ionization energy is very high because it involves removing an electron from a stable, noble gas-like configuration. This large jump in ionization energy explains why alkali metals form only +1 ions in compounds.

20. How do the melting points of alkali metal halides compare, and why?

The melting points of alkali metal halides generally decrease as we move down the group (from Li to Cs) for a given halide. This trend is due to the increasing size of the cation, which leads to weaker lattice energy. However, for a given alkali metal, the melting points increase as we move from fluoride to iodide, due to increasing polarizability of the anion.

21. What is the role of alkali metals in biological systems?

Alkali metals, particularly sodium and potassium, play crucial roles in biological systems. They are involved in maintaining osmotic balance, transmitting nerve impulses, and regulating heart function. Sodium is primarily found in extracellular fluids, while potassium is more abundant inside cells. Their concentration gradients across cell membranes are essential for many physiological processes.

22. How do alkali metals form alloys, and what are some applications?

Alkali metals can form alloys with each other and with some other metals. For example, sodium-potassium alloy (NaK) is liquid at room temperature and used as a heat transfer medium in some nuclear reactors. Lithium alloys are used in aircraft construction due to their low density and high strength-to-weight ratio.

23. Why do alkali metals have low electron affinities?

Alkali metals have low electron affinities because their valence shells are already complete (ns1 configuration). Adding an electron would require placing it in the next higher energy level, which is energetically unfavorable. This is why alkali metals prefer to lose electrons rather than gain them in chemical reactions.

24. How does the solubility of alkali metal compounds in water compare to other metal compounds?

Most alkali metal compounds are highly soluble in water due to the strong hydration of the small, highly charged alkali metal ions. This is in contrast to many other metal compounds, which may have limited solubility. The high solubility of alkali metal compounds contributes to their widespread distribution in nature and their importance in biological systems.

25. What is the significance of the alkali metal ion's hydration energy?

The hydration energy of alkali metal ions is significant because it affects their behavior in aqueous solutions. As we move down the group, the hydration energy decreases due to increasing ionic size. This trend influences properties such as solubility, mobility in solution, and the ability to form complexes. Understanding hydration energies is crucial in fields like electrochemistry and solution chemistry.

26. How do alkali metals interact with ammonia, and what are the resulting solutions called?

Alkali metals dissolve in liquid ammonia to form deep blue solutions. These solutions, called metal-ammonia solutions, contain solvated electrons and metal cations. The blue color is due to the presence of solvated electrons. At higher concentrations, the solutions become bronze-colored and metallic. These solutions are powerful reducing agents and have applications in organic synthesis.

27. Why do alkali metals form peroxides and superoxides, and how does this behavior change across the group?

Alkali metals form peroxides (O2^2-) and superoxides (O2^-) because they can stabilize these oxygen anions. The tendency to form these compounds increases down the group due to the increasing size of the cation. Lithium forms only the oxide (Li2O), sodium primarily forms the peroxide (Na2O2), while potassium and heavier alkali metals form superoxides (KO2, RbO2, CsO2). This trend is related to the lattice energy and the stability of the oxygen species.

28. How do the atomic and ionic radii of alkali metals compare to those of other elements in the same period?

Alkali metals have the largest atomic and ionic radii among elements in their respective periods. This is because they have the lowest effective nuclear charge, allowing their electron clouds to expand more. When they form cations, they lose their outermost electron but retain the same number of electron shells, resulting in ionic radii that are still larger than most other elements in the same period.

29. What is the photoelectric effect, and how does it relate to alkali metals?

The photoelectric effect is the emission of electrons from a material when it's exposed to light. Alkali metals exhibit this effect strongly due to their low ionization energies. When light of sufficient energy strikes an alkali metal surface, it can easily eject electrons. This property made alkali metals important in the early study of the photoelectric effect and led to applications in photocells and early television camera tubes.

30. How do alkali metals behave in non-aqueous solvents compared to water?

In non-aqueous solvents, alkali metals often exhibit different behavior compared to water. For example, in liquid ammonia, they dissolve to form solvated electrons without producing hydrogen gas. In organic solvents like ethers, they can form organometallic compounds. The reactivity in non-aqueous solvents is generally lower than in water, allowing for different types of reactions and applications, particularly in organic synthesis.

31. Why do alkali metals form complexes less readily than transition metals?

Alkali metals form complexes less readily than transition metals because they lack d-orbitals for bonding and have a lower charge-to-size ratio. Their large size and single positive charge make them poor at attracting and holding ligands. When alkali metals do form complexes, they tend to have high coordination numbers and form weaker bonds compared to transition metal complexes.

32. How does the reactivity of alkali metals with nitrogen compare to their reactivity with oxygen?

Alkali metals are generally less reactive with nitrogen compared to oxygen. While they react readily with oxygen at room temperature, they typically require heating to react with nitrogen. The product of the reaction with nitrogen is a nitride (M3N), where M is the alkali metal. Lithium is the most reactive with nitrogen, forming lithium nitride (Li3N) more easily than other alkali metals.

33. What is the role of alkali metals in the production of organometallic compounds?

Alkali metals play a crucial role in the production of organometallic compounds, particularly in the synthesis of organic molecules. They are used to prepare strong bases and reducing agents like butyllithium and sodium naphthalenide. These organometallic reagents are essential in organic synthesis for creating carbon-carbon bonds and performing various transformations that would be difficult or impossible with other reagents.

34. How do alkali metals contribute to the properties of glass?

Alkali metals, particularly sodium and potassium, are important components in many types of glass. They act as flux agents, lowering the melting point of silica and making glass formation easier. However, they also make the glass more susceptible to chemical attack and thermal shock. The ratio of different alkali metals can be adjusted to fine-tune the properties of glass, such as its thermal expansion coefficient and chemical durability.

35. Why do alkali metals have relatively low melting points compared to other metals?

Alkali metals have low melting points compared to other metals due to their weak metallic bonding. With only one valence electron per atom contributing to the bonding, the cohesive forces between atoms are relatively weak. This allows the crystal structure to break down at lower temperatures compared to metals with stronger metallic bonds, resulting in lower melting points.

36. How do alkali metals behave in flames, and what is the principle behind flame photometry?

When introduced into a flame, alkali metals produce characteristic colors due to the excitation and subsequent relaxation of their valence electrons. This property is the basis of flame photometry, an analytical technique used to detect and quantify alkali metals in samples. Each alkali metal produces a distinct color: lithium (red), sodium (yellow), potassium (lilac), rubidium (red-violet), and cesium (blue). The intensity of the color is proportional to the concentration of the metal in the sample.

37. What is the significance of the alkali metal-graphite intercalation compounds?

Alkali metal-graphite intercalation compounds are formed when alkali metal atoms are inserted between the layers of graphite. These compounds have interesting electrical and chemical properties. They can be superconductors at low temperatures and are highly reactive. Lithium-graphite intercalation compounds are particularly important as they form the basis for the anodes in many lithium-ion batteries, enabling high energy storage capacity.

38. How do alkali metals interact with aromatic compounds, and what are the applications?

Alkali metals can react with aromatic compounds to form intensely colored solutions. For example, sodium reacts with benzene to form a green solution containing sodium benzene radical anions. This reaction, known as Birch reduction, is used in organic synthesis to reduce aromatic rings. Similar reactions are used in the production of alkali metal anions of polyaromatic hydrocarbons, which have applications in materials science and organic electronics.

39. Why are cesium atomic clocks more accurate than other types of atomic clocks?

Cesium atomic clocks are extremely accurate because they use the precise frequency of the electromagnetic waves emitted by cesium atoms during a specific electron transition. Cesium is particularly suitable because it has a large atomic mass (reducing the effects of atomic motion), a simple spectrum, and a transition frequency in the microwave region that's easy to measure. The accuracy of cesium clocks is due to the extremely consistent and stable nature of this atomic transition.

40. How do alkali metals contribute to the development of superconductors?

Alkali metals play a role in certain types of superconductors. For example, cesium has been used in the development of high-temperature superconductors. Alkali metal fullerides, compounds of alkali metals with buckminsterfullerene (C60), can exhibit superconductivity at relatively high temperatures. The alkali metals donate electrons to the fullerene molecules, creating a conducting system that can become superconducting under certain conditions.

41. What is the role of lithium in psychiatric medications, and how does it work?

Lithium is used as a mood stabilizer in the treatment of bipolar disorder and other psychiatric conditions. While its exact mechanism of action is not fully understood, it's believed to work by modulating neurotransmitter systems and affecting intracellular signaling pathways. Lithium can influence sodium transport in neurons and affect the metabolism of neurotransmitters like seroton