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Friday, 3 February 2017

Classification of elements and periodicity in properties of elements III


ELECTRO-NEGATIVE OR NON- METALLIC CHARACTERS: 
  • The tendency of an element to accept electrons to form an anion is called its non metallic or electronegative character. The elements having high electro-negativity have higher tendency to gain electrons and forms anion. So, the elements in the upper right hand portion of the periodic table are electro-negative or non-metallic in nature.
Periodicity:
(i) In period- The electro-negative or non- metallic characters increases from left to right in a period.

(ii) In group- The electro-negative or non-metallic characters decreases from top to bottom in a group.

REACTIVITY OF METALS:
Periodicity:
(i) In period- The tendency of an element to lose electrons decreases in a period. So the reactivity of metals decreases from left to right in a period.

(ii) In group- The tendency of an element to lose electrons increases in a period. So the reactivity of metals increases from top to bottom in a group.

REACTIVITY OF NON- METALS:
(i) In period- The tendency of an element to gain electrons increases in a period. So the reactivity of non-metals increases from left to right in a period.

(ii) In group- The tendency of an element to gain electrons decreases in a group. So the reactivity of non-metals increases from top to bottom in a group.

SOLUBILITY OF ALKALI METALS CARBONATES AND BICARBONATES:

PERIODICITY IN GROUP: The solubility of alkaline earth metal hydroxide and sulphates in water increases down the group (From Beryllium to Barium).

BASIC STRENGTH OF ALKALINE EARTH METAL HYDROXIDES:

PERIODICITY IN GROUP: 
The basic strength of alkaline earth metal hydroxide in water increases down the group (From Beryllium to Barium), i.e.,

Be(OH)2             <    Mg(OH)2    <     Ca(OH)2   <    Sr(OH)2      <     Ba(OH)
                    ------------------------------------------------------>
                                Basic strength increases

THERMAL STABILITY OF CARBONATES OF ALKALI AND ALKALINE EARTH METALS:
  • Except lithium carbonate, (LiCO3), the carbonates of all other alkali metals are stable towards heat, i.e., carbonates of alkali metals (except LiCO3) do not decompose on heating. LiCO3 decomposes on heating to give lithium oxide (LiCO3).
  • The carbonates of alkaline earth metals are relatively less stable. On heating, they decompose to give corresponding oxide and CO2 gas. The decomposition temperature for alkaline earth metal carbonates increases as we go down the group.
Anomalous Properties of Second Period Elements :


Their anomalous behaviour is attributed to their small size, large charge/radius ratio, high electro negativity, non- availability of d- orbitals in their valence shell. the first member of each group of p-Block elements displays greater ability to form pp-pp multiple bonds to itself (e.g. C=C, C≡C, O=O, N≡N) and to other second period elements (e.g. C=O, C≡N, N=O) compared to subsequent member of the group.


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