s-block Flashcards
why are group 1 elements called alkali metals
. Theseelements because of the highly alkaline nature of their water soluble hydroxides are
known as alkali metals.
why are they know as s-block elements
These elements are known as s-block elements as their last or valence electron enters in
the s-orbitals. These all are soft metals
electronic configuration
[noble gas] ns1
electropositive
Alkali metals are most electropositive elements and on moving down the group the
electropositive character increases. Therefore, they readily lose electron
alkali metal in size
The alkali metal atoms have the largest size and on moving down the group, the size of
atom increases. Low densities of alkali metals are due to their large size
alkali metals on reducing properties
Alkali metals are strong reducing agent down the group, their reducing nature increases.
alkali metals on ionic character
Alkali metal compounds are most ionic in nature and down the group, ionic character
increases
alkali metals on ionization enthalpy
The ionisation enthalpies of alkali metals are considerably low
and decreases down the group from Li to Cs.
alkali metals on hydration energy
Hydration enthalpy of alkali metal ions decreases with increase in ionic sizes
reactivity
The reactivity of these metals
increases down the group.
chemical properties(rx with air)
(1) Metal peroxides are diamagnetic
(2) The superoxides are paramagnetic in nature because ofthe presence of three electron bonds with one unpaired electron.
chemical properties (rx with liquid ammonia)
(1)The alkali metals dissolve
in liquid ammonia giving deep blue solutions which are
conducting in nature.
(2)The blue colour of the solution is due to the ammoniated
electrons. The solutions are paramagnetic and on standing,
slowly liberate hydrogen resulting in the formation of amide.
chemical properties(reducing agent)
Reducing power of alkali metals in
aqueous solution follows the trend: Li >Na> K> Rb> Cs .
The standard electrode potential (E °) which measures the
reducing power represents the overall change.
chemical properties(carbonates)
Alkali metals on exposure to air and
moisture get converted into oxides, hydroxides and
finally to carbonates,
notes: Alkali metals are normally kept in kerosene oil because of
their high reactivity towards air and water.
what is anomalous properties of lithium
● The anomalous behaviour of Li is due to exceptionally small size (like Mg) and high polarising power (i.e. charge/radius ratio) (like Mg) that exhibits some properties
