flourines are at axial or at equitorial in the structure of PF3Cl2 justify.?

Question

structure is trigonal bi pyramidal

Answer 1

Okay, your central atom is Phosphorous, and a glimpse at the periodic table shows you it is in column V, and therefore has five valence electrons. Trigonal Bi Pyramidial structure is simply a fancy way of saying the P atom has two bonds running up and down along the axis of the P atom, and three bonds lying flat in a plane around the equator of the P atom. Since there are only two choices for where the F and Cl atoms are, equatorial or axial, and since there are only two axial and three equatorial bonds, deduction, rather than true understanding of chemical bonding, tells us that the two Cl atoms are axial and the three F atoms are equatorial. Now I would suggest thinking about the radii of the F and Cl atoms, and doing some geometry to see how close the F and Cl atoms, can get to the P atom, and I will venture a guess that since F is highly electronegative (slightly moreso than Cl), that the F atoms can fit closer to the P atom if they are in the equatorial positions, than the Cl could if they were in the equatorial positions. By keeping the distances between the F and P small, we are reducing the potential energy of the molecule, which is thermodynamically favorable.

Answer 2

All 3 F atoms are equatorial and the 2 Cl atoms are axial.

This is because F has strong electron cloud of lone pairs on it due to its small size. so electronic repulsion b/w F and F is strong as compared to Cl to Cl or F to Cl repulsion. Therefore f atoms will try to be as far from each other as possible. So they will occupy Equatorial position as then the angle b/w any 2 f atoms is 120 deg. If any of the F atom occupy axial position it will be strongly repelled by another F atom located 90 deg apart. So, the former position is thermodynamically favourable.

Answer 3

Two of the fluorines are axial and one is equatorial. Large substituents are preferably equatorial because they only have two 90-degree interactions, whereas they would have three 90-degree interactions when placed axially. Small substituents therefore go to the axial positions. Lone pair electrons are the most sterically demanding substituents, and thus these are found in equatorial positions in, for example, the AX4E formulae. Flourine is less sterically demanding than chlorine for at least two reasons. Its atomic radius is smaller. Also, it pulls its electrons closer to itself more so than does chlorine, so there is less electron density near the phosphorus atom. Thus you want to put as many fluorines as possible at the axial positions. Of course only two can go axially, so the third has no choice but to go equatorial.