Alkali metal halide

Introduction

Alkali metal halides are basic compounds made up of alkali metals from Group 1 of the periodic table (such as lithium, sodium, and potassium) and halogens from Group 17 (such as fluorine, chlorine, and bromine). The combination of negatively charged halide ions (anions) and positively charged alkali metal ions (cations) characterizes these compounds as being ionic. This bonding results in strong ionic lattices with high melting and boiling temperatures. At normal temperatures, alkali metal halides usually have a white, crystalline solid appearance.

They have many applications, ranging from everyday ones like table salt (sodium chloride) to more specialist ones like photography, medicine, and materials research. Understanding their properties and reactivity facilitates the clarification of their roles in various industrial, scientific, and technical fields. In brief, being familiar with alkali metal halides' characteristics, structure, and uses provides insight into their many functions in the scientific, industrial, and technical fields emphasizing their significance for both forefront research and daily life.

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

Alkali Metal Halides

Alkali metals react with halogens to form ionic metal halides.
2M+X2→MX+ Heat

The reactivity order of alkali metals towards halogens is:
Cs>Rb>K>Na>Li

In ionic nature, solubility in H2O increases while lattice energy decreases.
For example:
LiF<NaF<KF<RbF<CsF
KF<KCl<KBr<KI

These halides are colorless, however, on heating, they become colored due to nonstoichiometry and crystal defects.

NOTE:

• LiF is ionic but insoluble in H₂O due to very high lattice energy while LiCl, LiBr, and LiI are covalent and hence are less soluble or insoluble as their hydration energy is less than lattice energy.
• Other MX are crystalline solids with high melting and boiling points.
• Halides of K, Rb, and Cs can also form polyhalides. For example:KI+I₂⟶KI₃

Recommended topic video on (Alkali Metal Halides)

Solved Examples Based On Modern Periodic Table

Q 1. Which among the following is least soluble in water?

1) RbF

2) KF

3) NaF

4) LiF

Solution:

Since LiF has the maximum lattice energy, thus it is the least soluble in water.

Hence, the answer is the option (4).

Q 2. Reason for the covalent nature of LiF :

1) Exceptionally small size of Li⁺ ion

2) High polarising power

3) Both 1 and 2

4) None of these

Solution:

As we learned,

Reasons for anomalous behavior of Lithium -

1. Exceptionally small size of its atom and ion

2. High polarising power or high charge/radius ratio

Hence, the answer is the option (3).

Conclusion

To sum up, alkali metal halides are a fundamental class of compounds that result from the interaction of alkali metals from Group 1 of the periodic table with halogens from Group 17. These compounds are ionic due to the interaction of positively charged alkali metal ions (cations) and negatively charged halide ions (anions). The materials have high melting and boiling temperatures due to the strong crystal lattices formed by this ionic bonding, and at ambient temperature, they typically look like white, crystalline solids. The significant hydration energy of alkali metal ions and the polarizability of halide ions are two factors that contribute to alkali metal halides' generally high solubility in water. Because of its solubility, aqueous solutions produce solutions that are transparent or have mild shades and can be applied to a number of practical situations.