General Characteristics of s-Block Elements
9 Apr 2018
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The
general characteristics of alkali metals (Li, Na, K, Rb, Cs and Fr) and
alkaline earth metals (Be, Mg, Ca, Sr, Ba and Ra), i.e.,
5-block elements are the following:
(i)
They are soft metals, possess low melting and
boiling points, have the largest atomic radii in their corresponding periods
and are good conductors of heat and electricity.
(ii)
They have low values of ionisation energies and
hence highly electropositive.
(iii)
They are very reactive and readily form ionic
compounds. They show a fixed valency which depends on the number of electrons
present in the outermost shell. The alkali metals show monovalency while
alkaline earth metals show divalency. They are never found in free state in
nature due to their reactive nature.
(iv)
On account of low ionisation energies and highly
negative electrode potentials, they act as strong reducing agents. The alkali
and alkaline earth metals cannot be prepared by doing electrolysis of aqueous
solutions of their salts.
AD
(v) Except Be and Mg, they impart a characteristic colour to the flame.
(v) Except Be and Mg, they impart a characteristic colour to the flame.
(vi
i The compounds of 5-block elements are predominently ionic and
colourless. However, lithium and beryllium compounds are
covalent in nature.
(vii)
They have great
affinity for oxygen and non-metals. The oxides are basic. The hydroxides are
strong alkalies.
(viii)
They displace hydrogen
from acids and form corresponding salts.
(ix)
With exception of Be
and Mg, they decompose water and readily evolve hydrogen.
(x)
Fr and Ra are
radioactive elements. Cs and Fr are liquid elements while H is a gaseous
element. Helium is also a gaseous element but is included in group 18 or zero.
(M.pt. Cs = 28.5°C;
M.pt. Fr = 27°C)
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