Na, Mg and Al are the elements of the 3rd period of the Modern periodic Table having group number 1,2 and 13 respectively. Which one of these elements has the (i) highest valency, (ii) largest atomic radius, and (iii) maximum chemical reactivity? Justify your answer stating the reason for each.
OR

Based on the group valency of elements, state the formula for the following giving justification for each:

i. Oxides of group 1 elements

ii. Halides of the elements of group 13 and

iii. Compounds formed when an element of group 2 combines with an element of group 16.

Question

Na, Mg and Al are the elements of the 3rd period of the Modern periodic Table having group number 1,2 and 13 respectively. Which one of these elements has the (i) highest valency, (ii) largest atomic radius, and (iii) maximum chemical reactivity? Justify your answer stating the reason for each.
OR

Based on the group valency of elements, state the formula for the following giving justification for each:

i. Oxides of group 1 elements

ii. Halides of the elements of group 13 and

iii. Compounds formed when an element of group 2 combines with an element of group 16.

Philoid · Accepted Answer

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.

OR

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).