Question

This compound is characterized by ionic bonding between a group 1 metal cation and a tetrahedral anion. Write an appropriate Lewis structure for the anion and a specify a formal charge if there is one.

NaBF4

I looked up the answer and I have a few questions on why it is the answer. Why is the Na+ left on in the tetrahedral? I know a tetrahedral consists of 5 spots but I have 6 atoms I need to place. Also, how do I know that B is surrounded by the F rather than the Na?

Answer 1

1. The problem specifies that it is an ionic bond; therefore, the Na exists as a Na+ and the BF4^- as the anion. Is the Na^+ left on the tetrahedron in a drawing which you are looking at. I can't see the structure; perhaps the drawing you are looking at just as the Na^+ very close.The tetrahedral structure, then, consists of the B in the middle of the tetrahedron with a B at each of the four corners. (Does a tetrahedron have five "spots"? It has four sides; i.e., three sides that are triangles plus the bottom of the triangle (another triangle) so it has four corners or four "spots." I also don't see 6 atoms to place. You have A separate Na^+ and a separate BF4^- ion. The BF4^- then, as I said above, has the B in the middle of the tetrahedron with a F at each of the four corners.
2. Why is B surrounded by F than than the Na. Na is not a part of the structure. Note the problem states that NaBF4 is a compound characterised by an ionic bond between a metal I cation and a tetrahedral anion. Na is the metal I cation. BF4^- is the tetrahedral anion.
If this isn't clear to you, please try rephrasing your question and I'll take another crack at it.