structures of beryllium chloride in the solid state and vapour phase

Structures of Beryllium Chloride in the Solid State and Vapour Phase

Edited By Shivani Poonia | Updated on Jul 02, 2025 07:56 PM IST

Beryllium chloride (BeCl₂), an inorganic material, is an essential chemical reagent in numerous processes. The beryllium ion (Be²⁺) is well-known for its unique structure and properties because of its small size and high charge density. The inorganic compound beryllium chloride (BeCl₂) has unique structural characteristics depending on the phase it is in.

This Story also Contains

Structure of Beryllium Chloride
Solved Examples
Conclusion

Structures of Beryllium Chloride in the Solid State and Vapour Phase

Solids Phase:

In its solid state, beryllium chloride forms a polymeric chain structure. Every beryllium atom is tetrahedrally linked to four chlorine atoms, while every chlorine atom connects two beryllium atoms. Consequently, BeCl₄ tetrahedra are linked by a one-dimensional chain consisting of common chloride ions. The bonding can be described as ionic with significant covalent character due to the Be^3⁺ ions small size and high charge density.

Gas Phase:

In the gas phase, beryllium chloride exists as distinct BeCl₂ molecules. Each BeCl₂ molecule assumes a linear shape with a 180° bond angle, which is indicative of sp hybridization of the beryllium atom. Covalent bonds make up the bulk of a molecule's bonding.

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

Structure of Beryllium Chloride

All metals on heating with halogens from halides of type MX₂M+X2→MX2
BeCl₂ cannot be prepared in aqueous solution due to the formation of hydrated ion [Be(H₂O)₄]²⁺.
BeCl₂ can be prepared by heating BeO in the presence of coke in a current of chlorine gas.
Structure of BeCl₂
- In Solid State:
- In Liquid State: Two forms of BeCl₂ exist at different temperature. Above 1200K, a monomeric form exists as shown below.
  
  Below 1200K, dimeric form exists as shown below.

A "covalent alkaline earth metal halide" refers to a compound composed of an alkaline earth metal (Group 2 elements like beryllium, magnesium, calcium, etc.) and a halogen (Group 17 elements like fluorine, chlorine, bromine, iodine, etc.) in which the bonding involves the sharing of electron pairs between the metal and the halogen atoms, indicating a covalent bond.

These compounds typically form when the electronegativity difference between the metal and halogen atoms is not significant enough to warrant a complete transfer of electrons, leading to a shared electron pair between the atoms. Examples include beryllium fluoride (BeF₂), magnesium chloride (MgCl₂), and calcium bromide (CaBr₂). These compounds often have high melting and boiling points due to the strong directional covalent bonds between the metal and halogen atoms, and they may exhibit some degree of solubility in polar solvents due to their polar nature.

Solved Examples

Example:1

Q 1. The structure of beryllium chloride in the solid state and vapour phase, respectively, are :

1) Chain and chain

2) Dimeric and dimeric

3) Chain and dimeric

4) Dimeric and chain

Solution-
As we learned-

Structure of Beryllium chloride in vapour and solid phase. -

A. In vapour state, it exists as a chlorine bridge dimer.

B. In the solid state, BeCl₂has a polymeric structure with chlorine bridges.

BeCl₂ is an electron-deficient compound with sp hybridization. Therefore in the solid state, it combines with another BeCl₂ molecule to give Be₂Cl₄ by forming a coordinate bond between Cl and Be thus attaining more stability

However, in the gaseous state, it exists as a single molecule. At room temperature BeCl₂ is a polymeric solid, this is because it can form coordinate bonds with other molecules of the same type and forms a chain-like structure.

Therefore, option(3) is correct.

Example :2

Q.2 The covalent alkaline earth metal halide (X=Cl, Br,I) is:

1) MgX₂

2) CaX₂

3) BeX₂

4) SrX₂

Solution-

As we learned

Covalent alkaline earth metal halide:-

In chemical terms, all of the alkaline earth metals react with the Halogens to form the alkaline earth metal halides, all of which are ionic crystalline compounds except for Beryllium halide, which is a covalent [exception. BeCl₂].

A chain type of structure can be observed in the solid form of beryllium chloride.

These beryllium halides can be generally dissolved in organic solvents.

Hence, the answer is the option (3).

Conclusion

Beryllium chloride (BeCl₂) is a useful chemical for competitive examinations and applications in chemistry since it possesses distinct structural features in different phases. In the solid state, BeCl₂ forms a polymeric chain structure when beryllium atoms are linked to create a one-dimensional chain with significant covalent character. Each beryllium atom has a tetrahedral coupling to four chlorine atoms. BeCl₂ is observed as discrete linear molecules with sp hybridization and predominantly covalent bonding in the gas phase. The hydrated ion [Be(H₂O)₄]²⁺ is produced during the heating of BeO in the presence of coke and chlorine gas, rendering the production of BeCl₂ in an aqueous solution unfeasible. BeCl₂ exists as a monomeric form above 1200K and as a dimeric form below 1200K.

Frequently Asked Questions (FAQs)

1. How is the structure of BeCl₂ affected by temperature?

Above 1200 K, BeCl₂ is a monomer but at temperatures below it, the chlorine bridging that takes place changes it into dimers. These points mean structural stability.

2. What is the nature of the bond in BeCl₂?

BeCl₂ is covalent with appreciable solid-state ionic character. In the vapor phase, it is essentially covalent.

3. How is beryllium chloride prepared?

Beryllium chloride is prepared by heating beryllium oxide BeO along with coke in the presence of chlorine gas. Coke helps in the formation of the compound.

4. Is beryllium chloride soluble in organic solvents?

Yes, it is. The covalent nature of beryllium chloride lets it dissolve in organic solvents. Several advantages are accrued thereby.

5. What is the structure of beryllium chloride in the solid state?

In the solid state, beryllium chloride exists as a polymer. It forms a chain-like structure where each beryllium atom is tetrahedrally coordinated to four chlorine atoms, and each chlorine atom bridges two beryllium atoms. This results in a zigzag chain structure.

6. How does the structure of beryllium chloride change in the vapor phase?

In the vapor phase, beryllium chloride exists as discrete linear molecules. Each beryllium atom is bonded to two chlorine atoms, forming a BeCl2 molecule with a linear geometry and 180° bond angle.

7. Why does beryllium chloride form different structures in solid and vapor phases?

The difference in structures is due to the tendency of beryllium to achieve a stable electron configuration. In the solid state, it forms a polymer to achieve an octet, while in the vapor phase, it exists as linear molecules due to the high temperature and low pressure conditions.

8. What type of bonding exists in solid beryllium chloride?

Solid beryllium chloride exhibits covalent bonding between beryllium and chlorine atoms within the chains, and weak van der Waals forces between the polymer chains.

9. How does the coordination number of beryllium change from solid to vapor phase?

In the solid state, beryllium has a coordination number of 4 (tetrahedral). In the vapor phase, its coordination number reduces to 2 (linear).

10. Why doesn't beryllium chloride form an ionic lattice like other metal chlorides?

Beryllium chloride doesn't form an ionic lattice due to the high polarizing power of the small Be2+ ion and the low lattice energy that would result from an ionic structure. Instead, it forms covalent bonds and a polymeric structure in the solid state.

11. What is the hybridization of beryllium in solid beryllium chloride?

In solid beryllium chloride, beryllium adopts sp3 hybridization, allowing it to form four equivalent bonds in a tetrahedral arrangement.

12. How does the hybridization of beryllium change in the vapor phase?

In the vapor phase, beryllium in BeCl2 molecules adopts sp hybridization, resulting in a linear geometry with two bonds at 180° to each other.

13. Why is beryllium chloride considered an electron-deficient compound in its vapor phase?

In the vapor phase, beryllium in BeCl2 has only four electrons in its valence shell (two from each Cl), falling short of the octet rule. This makes it electron-deficient and highly reactive.

14. How does the electron-deficient nature of vapor-phase BeCl2 affect its reactivity?

The electron-deficient nature makes vapor-phase BeCl2 a strong Lewis acid, readily accepting electron pairs from Lewis bases to complete its octet.

15. What role does temperature play in the structural changes of beryllium chloride?

Temperature influences the phase transition of beryllium chloride. At higher temperatures (vapor phase), the polymeric structure breaks down into discrete linear molecules due to increased kinetic energy.

16. How does pressure affect the structure of beryllium chloride?

Higher pressures favor the polymeric solid structure, while lower pressures in the vapor phase allow for the formation of discrete linear molecules.

17. What experimental techniques can be used to study the structure of beryllium chloride in different phases?

X-ray diffraction can be used to study the solid-state structure, while gas-phase electron diffraction and spectroscopic methods like IR or Raman spectroscopy can be used to study the vapor phase structure.

18. Why is beryllium chloride considered a covalent compound despite being formed from a metal and a nonmetal?

The high charge density of the small Be2+ ion leads to significant polarization of the chloride ions, resulting in covalent bond formation rather than ionic bonding typically expected between metals and nonmetals.

19. How does the bond angle in beryllium chloride change from solid to vapor phase?

In the solid phase, the Cl-Be-Cl bond angles are approximately tetrahedral (109.5°). In the vapor phase, the bond angle in linear BeCl2 molecules is exactly 180°.

20. What is meant by the term "bridging chlorine" in the context of solid beryllium chloride?

"Bridging chlorine" refers to chlorine atoms that connect two beryllium atoms in the polymeric chain structure of solid beryllium chloride, forming Be-Cl-Be bridges.

21. How does the concept of electron-domain geometry apply to beryllium chloride in different phases?

In the solid phase, the electron-domain geometry around beryllium is tetrahedral. In the vapor phase, it is linear, with two electron domains around the central beryllium atom.

22. Why doesn't beryllium chloride form a dimeric structure like aluminum chloride in the vapor phase?

Unlike aluminum, beryllium is too small to accommodate more than two chlorine atoms around it in the vapor phase. Its small size and high electronegativity favor the formation of linear molecules rather than dimers.

23. How does the bond strength in beryllium chloride compare between the solid and vapor phases?

The Be-Cl bonds in the vapor phase are typically stronger than in the solid phase due to less electron sharing in the linear molecules compared to the polymeric structure.

24. What role does electronegativity difference play in the bonding of beryllium chloride?

The relatively small electronegativity difference between beryllium and chlorine contributes to the formation of covalent bonds rather than ionic bonds, influencing the compound's structure and properties.

25. How does the melting point of beryllium chloride compare to other alkaline earth metal chlorides, and why?

Beryllium chloride has a lower melting point compared to other alkaline earth metal chlorides due to its covalent nature and polymeric structure, which require less energy to break than the ionic lattices of other alkaline earth chlorides.

26. What is the significance of beryllium's small size in determining the structure of beryllium chloride?

Beryllium's small size results in a high charge density, leading to strong polarization effects. This influences its bonding behavior, favoring covalent bonds and unique structures in both solid and vapor phases.

27. How does the concept of polarizing power apply to beryllium in beryllium chloride?

Beryllium's high polarizing power, due to its small size and relatively high charge, distorts the electron clouds of the chloride ions, leading to covalent bond formation rather than ionic bonding.

28. Why is beryllium chloride considered a Lewis acid, and how does this relate to its structure?

Beryllium chloride is a Lewis acid because the beryllium atom has an incomplete octet and can accept electron pairs. This is particularly evident in the vapor phase where BeCl2 molecules are electron-deficient.

29. How does the solubility of beryllium chloride in non-polar solvents relate to its structure?

Beryllium chloride is soluble in non-polar solvents, especially in its vapor phase, due to its covalent nature and the formation of discrete, non-polar BeCl2 molecules.

30. What is the importance of van der Waals forces in solid beryllium chloride?

Van der Waals forces play a crucial role in holding the polymeric chains of beryllium chloride together in the solid state, contributing to its three-dimensional structure and physical properties.

31. How does the structure of beryllium chloride influence its electrical conductivity in different phases?

Solid beryllium chloride is a poor electrical conductor due to its covalent nature and lack of free ions. In the vapor phase, it's non-conductive as it exists as discrete, neutral molecules.

32. What is the relationship between the structure of beryllium chloride and its volatility?

The covalent nature and formation of discrete molecules in the vapor phase contribute to beryllium chloride's relatively high volatility compared to ionic metal chlorides.

33. How does the concept of resonance apply to the solid-state structure of beryllium chloride?

Resonance in solid beryllium chloride involves the delocalization of electrons along the polymeric chains, contributing to the overall stability of the structure.

34. Why is beryllium chloride considered an exception to the typical behavior of alkaline earth metal halides?

Beryllium chloride is exceptional due to its covalent bonding, polymeric solid structure, and molecular vapor structure, which differ from the ionic lattices typically formed by other alkaline earth metal halides.

35. How does the structure of beryllium chloride influence its reactivity with water?

The covalent nature and electron-deficient character of beryllium chloride, especially in the vapor phase, make it highly reactive with water. It undergoes hydrolysis, forming Be(OH)2 and HCl.

36. What role does orbital overlap play in the bonding of beryllium chloride in different phases?

In the solid phase, sp3 hybrid orbitals of beryllium overlap with p orbitals of chlorine to form tetrahedral structures. In the vapor phase, sp hybrid orbitals of beryllium overlap with p orbitals of chlorine to form linear molecules.

37. How does the concept of molecular polarity apply to beryllium chloride in its vapor phase?

Despite being composed of polar Be-Cl bonds, vapor-phase BeCl2 molecules are non-polar due to their linear geometry, which results in the cancellation of individual bond dipoles.

38. What is the significance of beryllium's tendency to form covalent compounds in understanding its chemistry?

Beryllium's tendency to form covalent compounds, as seen in beryllium chloride, is crucial for understanding its unique chemical behavior, reactivity, and the properties of its compounds.

39. How does the structure of beryllium chloride relate to its ability to act as a Friedel-Crafts catalyst?

The electron-deficient nature of beryllium in vapor-phase BeCl2 makes it an effective Lewis acid catalyst in Friedel-Crafts reactions, able to accept electron pairs from reactants.

40. What is the importance of understanding the structural changes of beryllium chloride in different phases for industrial applications?

Understanding these structural changes is crucial for optimizing industrial processes involving beryllium chloride, such as its use in the production of high-purity beryllium metal or as a catalyst.

41. How does the structure of beryllium chloride influence its ability to form complexes?

The electron-deficient nature of beryllium in BeCl2, especially in the vapor phase, allows it to readily accept electron pairs from ligands, forming various coordination complexes.

42. What is the relationship between the structure of beryllium chloride and its low boiling point compared to other metal chlorides?

The covalent nature and formation of discrete, linear molecules in the vapor phase contribute to beryllium chloride's relatively low boiling point compared to ionic metal chlorides.

43. How does the concept of electronegativity equalization apply to the bonding in beryllium chloride?

Electronegativity equalization in beryllium chloride results in the formation of polar covalent bonds rather than purely ionic bonds, influencing its structure and properties.

44. What role does electron delocalization play in the solid-state structure of beryllium chloride?

Electron delocalization along the polymeric chains in solid beryllium chloride contributes to the overall stability of the structure and influences its physical properties.

45. How does the structure of beryllium chloride relate to its ability to sublime?

The covalent nature and relatively weak intermolecular forces in solid beryllium chloride allow it to sublime more readily than typical ionic compounds, transitioning directly from solid to vapor phase.

46. What is the significance of beryllium's diagonal relationship with aluminum in understanding the structure of beryllium chloride?

The diagonal relationship between beryllium and aluminum helps explain some similarities in their chemistry, such as the tendency to form covalent chlorides, although their structures differ in the vapor phase.

47. How does the structure of beryllium chloride influence its behavior as a Lewis acid in different phases?

In both solid and vapor phases, beryllium chloride acts as a Lewis acid due to its electron-deficient nature. However, its Lewis acidity is more pronounced in the vapor phase where it exists as discrete, linear molecules.

48. What is the importance of understanding the structural changes of beryllium chloride in different phases for safety considerations?

Understanding these structural changes is crucial for safe handling and storage of beryllium chloride, as its reactivity and physical properties can vary significantly between phases.

49. How does the structure of beryllium chloride relate to its ability to form adducts with other molecules?

The electron-deficient nature of beryllium in BeCl2, particularly in the vapor phase, allows it to form adducts with electron-rich species, completing its octet through coordinate covalent bonding.

50. What role does crystal field theory play in understanding the solid-state structure of beryllium chloride?

While crystal field theory is more applicable to transition metal complexes, it can provide insights into the tetrahedral coordination of beryllium in the solid-state structure of beryllium chloride.

51. How does the concept of bond order apply to beryllium chloride in different phases?

The bond order of Be-Cl bonds in beryllium chloride remains consistent (single bonds) in both solid and vapor phases, but the overall electron distribution changes due to the structural differences.

52. What is the significance of understanding the structural changes of beryllium chloride in different phases for theoretical chemistry?

These structural changes provide valuable insights into bonding theories, molecular geometry, and the behavior of electron-deficient compounds, contributing to our broader understanding of chemical bonding and structure.

53. How does the structure of beryllium chloride influence its behavior in gas-phase reactions?

The linear, electron-deficient structure of vapor-phase BeCl2 molecules makes them highly reactive in gas-phase reactions, particularly as Lewis acids or in addition reactions.

54. What role does the concept of hybridization play in explaining the different structures of beryllium chloride in solid and vapor phases?

Hybridization explains the tetrahedral structure (sp3) in the solid phase and the linear structure (sp) in the vapor phase, demonstrating how electronic configuration influences molecular geometry and bonding.