Without consulting any tables, arrange the following substances in order and explain your choice of order: (a) Mg21, Ar, Br2, Ca21 in order of increasing radius (b) Na, Na1, O, Ne in order of increasing ionization energy (c) H, F, Al, O in order of increasing electronegativity

Explanation:

(a)  When we move across a period then there occurs a decrease in atomic size of the elements due to increase in force of attraction between the protons and electrons of an atom.

On the other hand, when we move down a group then there will occur an increase in atomic size of the elements due to increase in number of electrons which will also increase number of shells.

For example, Mg and Ca are group 2 elements, Br is a group 17 element and Ar is a group 18 element.

Hence, these are arranged in order of increasing radius as Ar < Br < Mg < Ca.

(b)  Ionization energy is defined as the energy required to remove the most loosely bound electron from a neutral gaseous atom.

When we move across a period from left to right then there occurs a decrease in atomic size of the atoms. Therefore, ionization energy increases along a period but decreases along a group.

Hence, order of increasing ionization energy for the given species is as follows.

                    Na < O < = Ne

(c)  Electronegativity is defined as the ability of an atom to attract electrons towards itself. When we move across a period then there occurs an increase in electronegativity of the atoms.

And, when we move down a group then there occurs a decrease in electronegativity of the atoms.

Therefore, for the given elements order of increasing electronegativity is as follows.

                       Al < H < O F

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2

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