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प्रश्न
What are the common physical features of alkali metals?
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उत्तर
Physical properties of alkali metals are as follows.
- They are quite soft and can be cut easily. Sodium metal can be easily cut using a knife.
- They are light coloured and are mostly silvery-white in appearance.
- They have low density because of their large atomic sizes. The density increases down the group from Li to Cs. The only exception to this is K, which has a lower density than Na.
- The metallic bonding present in alkali metals is quite weak. Therefore, they have low melting and boiling points.
- Alkali metals and their salts impart a characteristic colour to flames. This is because the heat from the flame excites the electron present in the outermost orbital to a high energy level. When this excited electron reverts back to the ground state, it emits excess energy as radiation that falls in the visible region.
- They also display a photoelectric effects. When metals such as Cs and K are irradiated with light, they lose electrons.
संबंधित प्रश्न
Why are lithium salts commonly hydrated and those of the other alkali metal ions usually anhydrous?
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Metallic elements are described by their standard electrode potential, fusion enthalpy, atomic size, etc. The alkali metals are characterised by which of the following properties?
(i) High boiling point.
(ii) High negative standard electrode potential.
(iii) High density.
(iv) Large atomic size.
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The valence shell electronic configuration of alkali metals is ______.
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Given below are two statements, one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Lithium salts are hydrated.
Reason (R) : Lithium has higher polarising power than other alkali metal group members.
In the light of the above statements, choose the most appropriate answer from the options given below :
