Barium is a group 2 (alkaline) element found on the left-hand side of the period

Question

Barium is a group 2 (alkaline) element found on the left-hand side of the periodic table with an atomic number (Z) of 56. It may be replaced in the BaCl_2 structure by calcium (Ca^2+), which is also a group 2 (alkaline) element with an atomic number (Z) of 20 to make CaCl_2. a) Based on your knowledge of the periodic table and its trends, if barium was replaced by calcium would you expect the number of anions surround each cation to change, and if so, how, and suggest a possible coordination number and coordination polyhedral that may result? [N.B. The number of CI^- surrounding each Ba^2+ is 8] b) Chlorine is a group VII (group 17) element found in the top-right hand corner of the periodic table with an atomic number (Z) or 17. When elemental chlorite ionizes to form an anion, what is the relative change in its radius (increase versus decrease) and explain your answer using appropriate electron orbital theory and nomenclature. c) Discuss, using appropriate tools such as the periodic table, whether you think that BaCI_2 and CaCl_2 represent an ionically or covalently bonded solid?

Explanation / Answer

QUESTION a

Ba ion is larger than the Ca ion. Thus Ba ion can accomodate more Cl ions around it. Thus the number of anions would decrease when Ba ion is replace by Ca ion.

Calcium chloride has the rutile structure with a coordination number of six. Thus the coordiantion polyhedral is octahedral.

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