Draw the structure of B F₄⁻ ion.

To draw the structure of the BF₄⁻ ion, we first need to understand its composition and the principles of molecular geometry. The BF₄⁻ ion consists of one boron atom (B) and four fluoride atoms (F), along with an overall negative charge. Let's break down the steps to visualize and understand its structure.

Step 1: Count the Valence Electrons

First, we need to determine the total number of valence electrons available for bonding:

• Boron (B) has 3 valence electrons.
• Each Fluorine (F) atom has 7 valence electrons, and since there are four fluorine atoms, that contributes 4 × 7 = 28 electrons.
• Since the ion has a -1 charge, we add one more electron to our total count.

So, the total number of valence electrons is:

3 (from B) + 28 (from F) + 1 (for the charge) = 32 valence electrons.

Step 2: Arrange the Atoms

In BF₄⁻, the boron atom will be at the center because it is less electronegative than fluorine. The four fluorine atoms will be arranged around the boron atom.

Step 3: Form Bonds

Each fluorine atom will form a single bond with the boron atom. A single bond consists of 2 electrons, so for four bonds, we will use:

4 bonds × 2 electrons/bond = 8 electrons.

After forming these bonds, we have:

32 total valence electrons - 8 used in bonding = 24 electrons remaining.

Step 4: Distribute Remaining Electrons

The remaining 24 electrons will be used to satisfy the octet rule for the fluorine atoms. Each fluorine needs 8 electrons to complete its octet. Since each fluorine is already sharing 2 electrons with boron, we need to add 6 more electrons (3 lone pairs) to each fluorine:

• Fluorine 1: 2 (bonding) + 6 (lone pairs) = 8 electrons.
• Fluorine 2: 2 (bonding) + 6 (lone pairs) = 8 electrons.
• Fluorine 3: 2 (bonding) + 6 (lone pairs) = 8 electrons.
• Fluorine 4: 2 (bonding) + 6 (lone pairs) = 8 electrons.

Step 5: Final Structure and Geometry

Now that we have all the electrons accounted for, we can visualize the BF₄⁻ ion. The structure will have the boron atom in the center with the four fluorine atoms symmetrically arranged around it. This arrangement leads to a tetrahedral geometry.

Summary of the BF₄⁻ Ion Structure

The final structure of the BF₄⁻ ion can be represented as follows:

• Boron (B) at the center.
• Four Fluorine (F) atoms at the corners of a tetrahedron.
• Each F atom has three lone pairs of electrons.

This tetrahedral shape is a result of the repulsion between the electron pairs, which pushes the fluorine atoms away from each other, creating a stable configuration.

In summary, the BF₄⁻ ion has a tetrahedral molecular geometry with boron at the center and four fluorine atoms surrounding it, each contributing to the overall stability of the ion.