S block: Group 1

Question 1

Electronic configuration

Answer 1

Li: [He]2s1
Na: [Ne]3s1
k:{ar}4s1
Rb:[Kr]5s1
Cs:[Xe]6s1

Question 2

Atomic and ionic radii

Answer 2

Largest in their respective periods. Increases down the group.

Question 3

Ionization Enthalapy

Answer 3

Low in general, decreases down the group.

Question 4

Hydration enthalapy

Answer 4

Energy released when 1 mol of a substance is dissolved into large amount of water. (always negative)
Decrease with increase in ionic size and decrease in charge/size ratio.

Li has maximum degree of hydratio, thus salt: LiCl.2H2O

Question 5

Density

Answer 5

Low density due to large atomic volume. Density increases down the group but K is lighter than Na

Question 6

State

Answer 6

soft, light metal.

Question 7

Conductors

Answer 7

good for both heat and electricity

Question 8

MP and BP

Answer 8

Low generally(weak metallic bonds), decreases down the group.

Question 9

Fame coloration

Answer 9

Due to low IE
Li: red
Na: yellow
K: violet
Rb: red-violet
Cs: blue

Question 10

Reducing properties

Answer 10

good reducing agents due to low IE

Question 11

Reaction w air

Answer 11

• creates oxides and moisture which then results in hydroxides.
• reactivity w oxygen increases from Li to Cs
• 4Li+O2 -> 2Li2O (oxide)
• 2Na + O2 -> Na2O2
• K/Rb?Cs + O2 -> kO2 (superoxide)

Stability is linked with relative sizes of anion and cation. Li forms oxide but Na+,K+ being larger form peroxides and superoxides

Li reacts directly with nitrogen to form nitrides Li2N

Question 12

Reaction w acids

Answer 12

readily reacts and liberates H2

M + HCl -> MCl + H2

Question 13

Nature of oxides

Answer 13

Oxides and peroxides -> Colourless
Superoxides-> yellow or orange, paramagnetic, used as oxidising agent

• all oxides are basic in nature and easily hydrolysed water to form hydroxides
  M2O + H2O -> 2M + 2OH-
  M2O2 + 2H2O -> 2M + 2OH- + H2O2
  2MO + H20 -> 2M + 2OH- + H2O2 + O2

Question 14

Reaction w water

Answer 14

• forms hydroxides and releases H2
  2M + H2O-> 2MOH + h2
• Li is less vigorous than the rest

Question 15

Nature of hydroxides

Answer 15

• strongest of all bases
• dissolve easily in water with evolution of heat due to intense hydration
• corrosive to skin- caustiic alkalis

Question 16

Reactivity towards halogens
among halides, what happens to covalent charecter? MP,BP of halides?
why low solubility of LiF and CsI?

Answer 16

react vigorously to form ionic halides.

• Li forms covalent halides due to high polarisation.
• among halides, covalent charecter increases from F to I
• MP and BP: F>Cl>Br>I
• Low solubility of LiF in water is due to high lattice enathalapy.
• Low solubility of CsI is due to small hydration enthalpy of two ions

Question 17

Reactivity towards Hydrogen

Answer 17

All metals react to form ionic hydrides which have high melting points (NaH)
- Ionic nature increases from Li to Cs

Question 18

Salts of Oxo - acids ( H+ on hydroxyl group) (Carbonates & bicarbonates)

Answer 18

• Forms salts of oxo-acids
• salts are soluble in water and thermally stable (increases down the group)
• • Li2CO3 decomposes on heating & its bicarbonates(HCO3-) does not exist as a solid.
  Li2CO3→ Li2O + CO2
  • Bicarbonates of other metals decompose at low temperature.
  • Nitrates: Lithium nitrate on heating gives oxide whereas other alkali metals give nitrites.
  4LiNO3 → 2Li2O + 4NO2 + O2
  2NaNO3 → 2NaNO2 + O2

Question 19

Lithium vs others (she’s not like other girls)

Answer 19

1) Li is harder, w higher BP and MP
2) Less reactive but stronger reducing agent
3) Li froms lithium monooxide and reacts directly w nitrogen to form nitrides
4) LiCl is deliquescent and forms hydrates like LiCl.2H2O
5) Lithium Hydrogen carbonate isnt formed in solid state
6) Lithium Nitrate on heating gives oxide (others give nitrites)
4LiNO3 -> Li2O + 4NO2 + O2
2NaNO3 -> 2NaNO2 + O2
7) LiF & Li2O are less soluble in water.

Question 20

Similarities between Li & Mg:

Answer 20

HORN-W

1) Atomic & ionic radii are almost the same.
2) Both are harder & lighter than other elements of their group.
3) Both react slowly with water. Their oxides & hydroxides are much less soluble in water.
4) Both react directly with nitrogen to form nitrides Li3N & Mg3N2.
5) Their oxides Li2O & MgO do not combine with excess of O2 to form superoxides.