S-block (Group 1) Flashcards
Melting and boiling point comparison between metal compounds and pure metals
metal compounds > pure metals
NaCl > Na
Elements showing photoelectric effect
K, Rb, and CS
It is best shown in Group 1
Commercially: mainly Cs is used
Li + N2 —>
Li + N2 –heat–> LiN3 –H2O–> LiOH + NH3
LiN3 –heat–> Li + N2
Atomic Size and Atomic volume trend
Increases top to bottom / down a group
Metallic surfaces become tarnish due to air oxidation so they are stored in
Organic compounds
Melting and boiling point order
Li > NA > K > Rb > Cs > Fr
Cs melts at 30*c (melts on palm)
Na + O2 —>
Na + O2 —> Na2O –excess air–> Na2O2 –excess air–> No reaction
Electropositive and metallic character
Increases down a group
Li + O2 —>
Li + O2 —> Li2O –in excess air–> no reaction (trace Li2O2)
Metallic Bond strength trend
Decreases down a group
mbs is prop to no of unpaired electrons
wrt other metallic groups alkali metals show comparatively weaker mbs
Reaction with H2O
and rate of reactions of all alkali metals
M + H2O —> MOH + H2
Li —> slowly
Na —> vigorously
K —> Violently
Rb/Cs —> explosively
Hydrated radius
Li+ > NA+ > K+ > Rb+ > Cs+
Ammonia detection test
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
Medium in which alkali metals are stored
All alkali metals are stored in kerosene except Li which is stored in paraffin wax.
Reaction with Halogens
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]
Electronegativity and ionization energy trend
Decreases down a group
Due to f-orbital contraction
EN Cs~Fr=0.7
IE Cs<Fr
Crystalline structure (Lattice arrangement)
Body centered cubic
almost shown in all alkali metals
Coordination number = 8
Reducing power in aqueous solution (electron losing ability)
Li > Cs > Rb > K > Na
Li has high HE
while others have low IE
Tritium radiation and half life
Tritium emits only beta radiations
Half life of tritium is 12.5 years
Metallic luster is due to
Oscillation of free electrons
Density order
Li < Na > K < Rb < CS
Na>K because of presence of vacant d orbital in K
M + O2 —>
(M=K/Rb/Cs)
M + O2 —> M2O –controlled air–> M2O2 –excess air–> MO2
Reaction with H2
M + H2 —> M+H- (ionic)
reactivity: Li > Na > K > Rb > Cs
