S-block (Group 1)

Question 1

Melting and boiling point comparison between metal compounds and pure metals

Answer 1

metal compounds > pure metals

NaCl > Na

Question 2

Elements showing photoelectric effect

Answer 2

K, Rb, and CS
It is best shown in Group 1
Commercially: mainly Cs is used

Question 3

Li + N2 —>

Answer 3

Li + N2 –heat–> LiN3 –H2O–> LiOH + NH3

LiN3 –heat–> Li + N2

Question 4

Atomic Size and Atomic volume trend

Answer 4

Increases top to bottom / down a group

Question 5

Metallic surfaces become tarnish due to air oxidation so they are stored in

Answer 5

Organic compounds

Question 6

Melting and boiling point order

Answer 6

Li > NA > K > Rb > Cs > Fr

Cs melts at 30*c (melts on palm)

Question 7

Na + O2 —>

Answer 7

Na + O2 —> Na2O –excess air–> Na2O2 –excess air–> No reaction

Question 8

Electropositive and metallic character

Answer 8

Increases down a group

Question 9

Li + O2 —>

Answer 9

Li + O2 —> Li2O –in excess air–> no reaction (trace Li2O2)

Question 10

Metallic Bond strength trend

Answer 10

Decreases down a group
mbs is prop to no of unpaired electrons
wrt other metallic groups alkali metals show comparatively weaker mbs

Question 11

Reaction with H2O

and rate of reactions of all alkali metals

Answer 11

M + H2O —> MOH + H2

Li —> slowly
Na —> vigorously
K —> Violently
Rb/Cs —> explosively

Question 12

Hydrated radius

Answer 12

Li+ > NA+ > K+ > Rb+ > Cs+

Question 13

Ammonia detection test

Answer 13

Hold a tube dipped out of HCl at the mouth of test tube containing aq. NH3 .
Observe the white fumes from the HCl tube.

NH3 + HCl —>NH4Cl

Question 14

Medium in which alkali metals are stored

Answer 14

All alkali metals are stored in kerosene except Li which is stored in paraffin wax.

Question 15

Reaction with Halogens

Answer 15

M + X2 —> MX (mostly ionic)

LiCl, LiBr, LiF are predominantly covalent.

For F2
ROR: Li > NA > K > Rb > Cs [LE]

For Br2/Cl2/I2
ROR: Cs > Rb > K > Na > Li [IE]

Question 16

Electronegativity and ionization energy trend

Answer 16

Decreases down a group
Due to f-orbital contraction
EN Cs~Fr=0.7
IE Cs<Fr

Question 17

Crystalline structure (Lattice arrangement)

Answer 17

Body centered cubic
almost shown in all alkali metals

Coordination number = 8

Question 18

Reducing power in aqueous solution (electron losing ability)

Answer 18

Li > Cs > Rb > K > Na

Li has high HE
while others have low IE

Question 19

Tritium radiation and half life

Answer 19

Tritium emits only beta radiations
Half life of tritium is 12.5 years

Question 20

Metallic luster is due to

Answer 20

Oscillation of free electrons

Question 21

Density order

Answer 21

Li < Na > K < Rb < CS
Na>K because of presence of vacant d orbital in K

Question 22

M + O2 —>
(M=K/Rb/Cs)

Answer 22

M + O2 —> M2O –controlled air–> M2O2 –excess air–> MO2

Question 23

Reaction with H2

Answer 23

M + H2 —> M+H- (ionic)

reactivity: Li > Na > K > Rb > Cs