S block: Group 1 Flashcards
Electronic configuration
Li: [He]2s1
Na: [Ne]3s1
k:{ar}4s1
Rb:[Kr]5s1
Cs:[Xe]6s1Atomic and ionic radii
Largest in their respective periods. Increases down the group.
Ionization Enthalapy
Low in general, decreases down the group.
Hydration enthalapy
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
Density
Low density due to large atomic volume. Density increases down the group but K is lighter than Na
State
soft, light metal.
Conductors
good for both heat and electricity
MP and BP
Low generally(weak metallic bonds), decreases down the group.
Fame coloration
Due to low IE Li: red Na: yellow K: violet Rb: red-violet Cs: blue
Reducing properties
good reducing agents due to low IE
Reaction w air
- 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
Reaction w acids
readily reacts and liberates H2
M + HCl -> MCl + H2
Nature of oxides
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
Reaction w water
- forms hydroxides and releases H2
2M + H2O-> 2MOH + h2 - Li is less vigorous than the rest
Nature of hydroxides
- strongest of all bases
- dissolve easily in water with evolution of heat due to intense hydration
- corrosive to skin- caustiic alkalis
Reactivity towards halogens
among halides, what happens to covalent charecter? MP,BP of halides?
why low solubility of LiF and CsI?
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
Reactivity towards Hydrogen
All metals react to form ionic hydrides which have high melting points (NaH)
- Ionic nature increases from Li to Cs
Salts of Oxo - acids ( H+ on hydroxyl group) (Carbonates & bicarbonates)
- 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
Lithium vs others (she’s not like other girls)
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.
Similarities between Li & Mg:
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.
