9. (6 points) We have looked at several different coordination numbers and the t
ID: 553465 • Letter: 9
Question
9. (6 points) We have looked at several different coordination numbers and the types of structures they form, based on the ratio rcra. However, we skipped over coordination number 5: the tables shown go from 4-fold coordination to 6-fold coordination. Suppose we have an arrangement of atoms in which there is one central atom (labeled A) and there are 3 atoms of a second type (labeled B) surrounding A in a plane. All four atoms are coplanar, and form a triangle as in the coordination number 3 example in your textbook. Now suppose we introduce two more B atoms, one to coordinate with A in the plane above, and one to coordinate with A in the plane below. This makes a trigonal bipyramidal structure with 5-fold coordination! (a) Suppose that every B atom is in contact with the A atom at the center. Will all of the B - B contacts along the edges of the polyhedron be the same length? (b) What is the minimum ratio of radii that would form this structure? Hint: calculate the ratio of rA to rB (c) Why do you think this structure is so rarely found in ionic crystals?Explanation / Answer
a) No, the edge length B-B will be different. The polyhedron triagonal bipyramid will have three short planar B - B bonds (equitorial) and two long (axial) B-B bonds
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.