METALS AND NON-METALS
METALLOIDS (SEMI METALS)
TYPICAL ELEMENTS :
DIAGONAL RELATIONSHIP :
Some elements of certain groups of 2nd period resemble much in properties with the elements of third period of next group i.e. elements of second and third period are diagonally related in properties. This phenomenon is known as diagonal relationship.
Diagonal relationship arises because of
(i) similar size of atom and ions
Li = 1.23 Å & Mg = 1.36 Å; Li+ = 0.60 Å & Mg2+ = 0.65 Å
(ii) similar electropositive characters
(iii) similar polarising powers (charge to radius ratio)
(iv) similarity in electronegativity values
(Li = 1.0 & Mg = 1.2; Be = 1.5 &AI = 1.5)
Similarities between properties of Li and Mg are as follows:
(a) Li and Mg both reacts directly with nitrogen to form lithium nitride (Li3N) and magnesium nitride (Mg3N2) whereas other alkali metals of I A group does not form nitride.
(b) Fluoride, carbonate and phosphate of Li and Mg are insoluble in water whereas these compounds of other alkali metals are soluble.
(c) Li and Mg both are hard metals, whereas other metals of I A group are soft.
(d) LiOH and Mg(OH)2 both are weak bases, whereas hydroxides of other elements of IA group are strong base.
(f) Metallic bond in Li and Mg both are strong compare to other alkali metals.
(g) Their melting and boiling points are high.
(h) By thermal disintegration of LiNO3 and Mg (NO3)2 ; Li2O and MgO is obtained respectively.
(I) Thermal stability of Li2CO3 and Mg CO3 is very less compare to other alkali metals and they liberates CO2 gas easily.
Similarly, Be shows similarity to Al of IIIA group compare to other elements of IIA group which are as follows:
(a) These both elements do not provide colour to Bunsen burner.
(b) They both are comparatively stable in air.
(c) Both are insoluble in NH3, therefore, do not form blue coloured solution.
(d) There is no tendency of making peroxide and superoxide in them.
(e) Reducing power is very less due to low value of standard electrode potential in the form of oxidation potential.
(f) Be and AI both forms halogen bridge halides.