Atomic number of Sodium: 11
Atomic number of Magnesium: 12
Atomic number of Aluminium: 13
Electronic configuration of the given elements:
Na(Sodium) : 2,8,1 (11 electrons)
Mg(Magnesium): 2,8,2 (12 electrons)
Al (Aluminium): 2,8,3 (13 electrons)
i) Valency is the power of an atom to combine with another atom by donating or receiving electrons in their outermost shell or Valency is the number of electrons gained or lost by an element to achieve stable noble gas configuration which is a fully filled octet. Aluminium has the highest valency since it loses three valence electrons to attain stable electronic configuration of a noble gas.
ii) Sodium has the largest atomic size. We know that atomic size decreases on moving from left to right across a period due to increase in nuclear charge decreasing the atomic size.
iii) Maximum chemical reactivity is of sodium (Na) because as we can see that all the three elements are metals and the chemical reactivity of these elements is determined by their metallic character (tendency to lose electrons). We know that the tendency to lose electrons decreases from left to right across a period hence sodium has the highest chemical reactivity.
I) Valency of group I elements is 1. And valency of oxygen is 2. Hence, formula of oxides of group I elements is A2O (where A is the group I element and O is oxygen).
II) Valency of group 13 elements is 3. And valency of halogens (halides) is 1. Therefore, the formula of halides of group 13 elements is MX3 (where M is the group 13 element and X is the halogen).
III) Valency of element of group 2 is 2 and that of group 16 is also 2. Hence, the formula of the compound formed is X2Y2or XY. (where X is the element of group 2 and Y is the element of group 16).
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