S-BLOCK

Basic definations:
1A Alkali metals: Their oxides/hydroxides are strongest bases irresepective of periods.

2A Alkaline earth metals: Because of their carbonates they are most abundant in earth's crust and basic in nature.

PHYSICAL PROPERTIES:

1. Atomic size:

1A > 2A > d-block

2. Sonority is the property to produce sound for longer time due to collision b/w the atoms if once hammered

3.High conductivity: due to presence of free electrons,ions and low Ionization energy

4. LUSTROUS BEHAVIOUR: Due to oscialltion of free electron by absorption of energy from photons

5. Metallic bond strength decreases downward

Metallic bond strength 1/metallic character number of unpaired electron

6. Softness: It decreases left to right. 1A are softest metals due to weakest metallic bond strength or due to crystalline properties. Softness increases downward.

7. Brittleness: It decreases from right to left. Hence these s-block metals are very very less brittle.

Brittleness is the separtion of layers of the particles from the crystal structure by applying the force at a point.

U cn also undrstnd like this: Metal Jitna soft hoga utna hi mushkil hoga uski layers ko separate karna.

8. Crystal structure:

1A similar crystal lattice.

2A dissimilar crystal lattice.

1A physical properties show regular trend

2A phys. prop. show irregular trend.

9. 1A: melting and boiling point decrease downard regularly due to decrease in metallic bond strength

2A: MP and BP decreease dwnwrd irregularly due to different crystal structures.

The BP and MP of s-block metals is less than d block metals due to stronger metallic bond strength in d block elements.

10. DENSITY: It increases downward due to poor shielding effect and increase in atomic mass.

1A Li<K

2A Ca

Li, K and Na are lighter than water

K

there is SUDDEN EXPANSION in volume of K and Ca

therefore their density is low.

Be has high density because of different LATTICE STRUCTURE

The density of d-block metals is greater than s-block metals due to low atomic mass and high volume of s-block metals...

10. PHOTOELECTRIC EFFECT:

In all metals of s block only K, Rb, Cs give photoelectric effect. They are used in photoelectric effect due to high Ionization energy.

11. FLAME TEST:

s-block salts like NO3-, NO2-, SO42-etc...

are heated on bunsen burner the salt absorbs heat radiations and then releaes energy which belongs to visible part of the spectrum which produces colours. On the basis of colour we can decide the elements..

NOTE: Be and Mg dunno give flame test due to high IE.

Platinum wire is taken due to its inertness and SEMI-SOLID form is taken of the salt due to low IE.

Halides are taken because of emission of high volatile radiation.

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Li Crimson Red

Na Golden Yellow

K Purple/lilac/plane violet

Rb violet

Cs Blue

NOTE: LILAC colour of K has been asked in JEE

Be X

Mg X

Ca Brick

Sr Crimson Red

Ba Apple Green

NOTE: wavlength increases downward and frequency upward.

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All S-block compounds are dimagnetic(exceptions alwys dere)

FLAME TEST is significant for s-block elements because all elements are white in colour and water soluble...

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CHEMICAL PROPERTIES:

1. Chemical reactivity:

Q. What happens when Na is left open in air ?

A. Na in air gives Na₂O

Na₂O comes in contact of water present in atmosphere and it fomrs NaOH

NaOH comes in contact with carbon dioxide of air and forms Na₂CO₃.

Na forms carbonates at end.

Metals like Fe and Al loose their lusturous behaviour due to formation of oxides.

All s-block elements follow the same reaction.

Therefore they can't be kept free in air as they are too reactive.

Hence they are stored in organic solvents like Carbon Tetrachloride, pyridene, toulene, benzene except Be, Mg and Li

Be and Mg form stable layer of oxides. Thus they can be kept freely in water or air.

IMP: Li is stored in wax. it can't be STORED IN KEROSENE because its density is less than that of kerosene. ( IT FLOATS ON THE SURFACE OF KEROSENE)

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SOLUBILITY:

The solubility of compounds of s-block elements with NO3-,HCO3-, OH-, H-, O2- and many other anions INCREASES DOWN THE GROUP.

FOR all 1A compounds the SOLUBILITY WILL INCREASE DOWN THE GROUP (except for Chlorides...itz an exception cn't do much about it).

The same fate will follow for 2A compounds....

BUT THERE ARE IMPORTANT EXCEPTIONS OF COMPOUNDS WHICH HAVE TO BE LEARNED:

Carbonates, MnO4-, Sulphates.

in these compounds the solubility decreases downward (ONLY 2A)

The reason is in these compounds Lattice energy > Hydration energy.

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