How do you draw the Lewis structure of phosphorus pentachloride?

To draw the Lewis structure of phosphorus pentachloride (PCl₅), we need to follow a systematic approach that involves understanding the valence electrons of the atoms involved and how they bond together. Let’s break it down step by step.

Step 1: Determine the Total Number of Valence Electrons

First, we need to find out how many valence electrons are present in phosphorus pentachloride. Phosphorus (P) is in group 15 of the periodic table and has 5 valence electrons. Chlorine (Cl), being in group 17, has 7 valence electrons. Since there are five chlorine atoms in PCl₅, we calculate the total valence electrons as follows:

• Valence electrons from phosphorus: 5
• Valence electrons from chlorine: 5 × 7 = 35

Adding these together gives us:

Total valence electrons = 5 + 35 = 40

Step 2: Arrange the Atoms

In PCl₅, phosphorus is the central atom because it can expand its octet, while chlorine atoms will surround it. The arrangement will look like this:

• Phosphorus (P) in the center
• Five chlorine (Cl) atoms surrounding the phosphorus

Step 3: Connect the Atoms with Single Bonds

Next, we connect each chlorine atom to the phosphorus atom with a single bond. Each bond consists of two electrons. Since there are five bonds, we will use:

5 bonds × 2 electrons/bond = 10 electrons

Step 4: Distribute Remaining Electrons

After forming the bonds, we subtract the electrons used from the total valence electrons:

40 total electrons - 10 used in bonds = 30 electrons remaining

Now, we distribute these remaining electrons to the chlorine atoms. Each chlorine atom needs 8 electrons to complete its octet. Since each chlorine already has 2 electrons from the bond with phosphorus, we need to add 6 more electrons (3 lone pairs) to each chlorine atom:

• Chlorine 1: 2 (bond) + 6 (lone pairs) = 8 electrons
• Chlorine 2: 2 (bond) + 6 (lone pairs) = 8 electrons
• Chlorine 3: 2 (bond) + 6 (lone pairs) = 8 electrons
• Chlorine 4: 2 (bond) + 6 (lone pairs) = 8 electrons
• Chlorine 5: 2 (bond) + 6 (lone pairs) = 8 electrons

After placing the lone pairs, we have used:

5 chlorine atoms × 6 electrons = 30 electrons

Final Structure

Now, we have used all 40 valence electrons, and each chlorine atom has a complete octet. The Lewis structure of phosphorus pentachloride can be represented as follows:

Phosphorus is in the center with five single bonds to each chlorine atom, and each chlorine has three lone pairs of electrons. This structure indicates that phosphorus can accommodate more than eight electrons, which is characteristic of elements in the third period and beyond.

Visual Representation

While I can't draw it here, you can visualize it like this:

Cl Cl Cl

\ | /

P

/ | \

Cl Cl

This structure illustrates the bonding and lone pairs clearly. Understanding this process helps in drawing Lewis structures for other molecules as well, as the same principles apply.