All alkali metals form various oxides, hydroxides, carbonates and nitrates. They are hence, known as the most reactive elements as they have the weakest nuclear charge in the respective period. They have the tendency to lose their one valence electron in the last shell and form strong ionic bonds with their anions. Let’s, one by one study the characteristics of the compound of the alkali metals.
1. Forming Oxides and Hydroxides
The property of alkali metals allows their oxides, their peroxides and their super-oxides to dissolve in water quite readily. Such dissolving in water produces corresponding hydroxides which are basically very strong alkalis. Certain examples in the form of a chemical equation that display such phenomenon are as follows:
It will be right to say that peroxides and super-oxides act as oxidising agents since they are able to react with water to form hydrogen oxide and oxygen easily. For any hydroxide of an alkali metal, one can observe whitish crystalline solids. As a base, they are very strong and can easily dissolve in water, also emitting a large quantity of heat in the process.
Moving down the periodic table, we can observe that the basic strength of such hydroxides, tends to increase. The hydroxides of alkali metals usually behave as strong bases owing to their low ionization energies which go down in the group. This decrease in ionization energies usually leads to the weakening of the bond between the metal and hydroxide ions and M – O bond in M – O – H can easily break, hence giving M+ and OH–
This ultimately results in increased concentration of hydroxyl ions in the solution which can be defined by the increase in basic characters. All such hydroxides are very soluble in water and thermally stable with the exception of lithium hydroxide. Alkali metals with their hydroxides, being strongly basic, tend to react with all acids, leading to the formation of salts.
2. Forming Halides
The alkali metals tend to combine directly with different halogens under appropriate conditions, thus forming halides of the general formula MX. Examples that demonstrate the formation of such halides are as follows:
(where M = Li, Na, K, Rb or Cs and X = F, Cl, Br or I). All of these halides are usually colourless, are high melting crystalline solids that have high negative enthalpies of formation.
3. Other Compounds of the Alkali Metals
Q. Why does lithium form only lithium oxide and not peroxide or superoxide?
Ans: Due to the small size of lithium compounds, the element has a strong positive field around it. When combined with the oxide anion (O2–), the positive field around the lithium-ion restricts the spreading movement of the negative charge towards another oxygen atom and thus prevents the formation of higher oxides. This is why lithium does not form lithium peroxide or lithium superoxide and gets restricted to only lithium oxide.
|1. What are the common characteristics of compounds of the alkali metals?
|2. What types of compounds do alkali metals typically form?
|3. How does the solubility of alkali metal compounds in water contribute to their reactivity?
|4. Why are alkali metal compounds often used as catalysts in chemical reactions?
|5. How do alkali metal compounds contribute to the vibrant colors observed in fireworks?