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Candidates who are preparing for their CSIR NET exam might need to get some short study notes and strategies to apply while preparing for the key exam of their life. At this point in time, We at Gradeup come up with short notes on Alkali Metal Trends which comes under the Inorganic Chemistry section of the Chemical Science syllabus.
This set of short notes on Alkali Metal Trends has been meticulously designed by our experienced subject-matter experts to give you the most standard set of study materials to be focused upon. In this cut-throat competitive world, students need to prepare themselves with the best study materials to help them in the learning process and for their future. Here we are offering the best study notes that are reliable and can be used by the students during their preparations for the upcoming CSIR-NET 2021 exam.
Study Notes on Alkali Metal (Group 1)Trends
1. All metals are malleable and tend to become softer down the group. For instance, Lithium can be cut by knife, whereas, Rb and Cs are of the consistency of putty.
2. Reactivity of metals towards O2 and H2O increases as we go down the group.
Reaction with H2O
Reaction with O2
Li reacts slowly
Li forms Li2O
Na reacts vigorously
Na forms Na2O2
K evolves H2
K forms KO2
Rb and Cs are explosive
Rb and Cs forms RbO2 and CsO2 respectively
3. Lithium does not replace protons on PhC=CH, whereas, all other elements from the group do.
4. Group 1 elements generally form ionic compounds, with Lithium being an exception.
5. They form a wide range of salts with ionic properties; such as-
- High Melting Points.
- Water solubility that gives conducting solutions.
- Halide salts are ionic and are not hydrolysed.
- Basic nature of oxides and hydroxides.
- Their hydrides are ionic, basic and are strong reducing agents.
6. Thermal stability of their sulphates, carbonates, nitrates, peroxides, and superoxide increases as we go down the group.
7. With the increase in the size of metal atoms, any electron pair which is bonded becomes farther from the nucleus of metal and it gets least attracted towards the same. This leads to a decrease in electronegativity down Group 1.
8. Solubility of hydroxide in water increases as we go down the group.
LiOH < NaOH < KOH < RbOH < CsOH
9. Lithium possess a high charge/size ratio, which leads to anomalies, such as-
- LiH is more stable than other hydrides.
- Li2CO3 is very much less stable than other carbonates in the group.
- Lithium salts are less soluble in water whereas, more soluble in organic solvents.
- Li and Na form a number of hydrated salts. Whereas, K forms some hydrated salts and Rb and Cs does not form any hydrated salts.
10. Alkali metal ions do not readily form complexes with ligands such as NH3 or CN- but form complexes with polydentate ligands or chelates, such as crown ethers and cryptands.
The bonding in the complex ions is primarily electrostatic, i.e., ionic, and very hard; and the relative size of cation and cavity plays an important role. For instance, the complex ions with 18-crown-6 ether ligand follows the order of stability: Li+ < Na+ < K+ < Rb+ < Cs+. This implies that different ring sizes prefer different ions. For example,
12-crown-4 and 15-crown-5 prefers Li+;
24-crown-8 prefers Rb+ and Cs+.
11. RLi are used as reagents in organic chemistry as they’re readily synthesized. These are soluble in organic solvents and provide a slightly more reactive source of carbanions than the Grignard reagent, RMgX.
RLi compounds also form oligomers or clusters in the form of rings and polyhedral which have hydrocarbon residues which dominate the surface.
In comparison to this, Alkyls of Na and K are more ionic in nature and form an infinite 3-D structure in its solid state. These are soluble in hydrocarbons and are also extremely air/moisture sensitive.
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