Question

Use the principle of periodic trends and chemical bonding to explain the following observations. The atomic radius of Nais 1.86X10 -10 m and the atomic radius of Rb is 2.48X 10 -10 m The firs ionization energy of Na is 496kJ/mol and the first ionization energy of Cl is 1251 kJ/mol The formula of sodium chloride is NaCl and the formula of potassium chloride is KCl The formula of sodium chloride is NaCl and the formula of magnesium chloride is MgCl2

Answer 1

As we go down the group the electrons enters in new valency shells as a result the size of atoms increases. Therefore size of Rb is greater than that of Na.

Ionization enthalpy is the energy to required to remove the valency electron from atom or ion. In sodium there is only one valency electron and loosing it makes it stable by forming a octet configuration also adding to it the valency electron is attracted by only 11 protons. In case of chlorine the valency electron is attracted by 17 protons and gaining 1 electron makes it octet in it's valency shell and hence the Ionization enthalpy of chlorine is greater than sodium.

Sodium and potassium are in first group and they have only one loosely bound valency electron in it's valency shell, loosing this they form highly stable octet configuration and hence they form chlorides of type MCl. Whereas Magnesium belongs to second group and has 2 valency electrons and hence it forms MgCl2.

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