What is the shape and bond angle of PH3? Explain
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The shape of a molecule is determined by its molecular geometry, which is in turn influenced by the arrangement of its atoms and the number of electron pairs around the central atom. To determine the shape and bond angle of PH3 (phosphine), we can follow these step-by-step explanations:
Step 1: Draw the Lewis structure of PH3:
Start by determining the total number of valence electrons. Phosphorus (P) is in Group 5A of the periodic table, so it has 5 valence electrons. Hydrogen (H) is in Group 1A, so each hydrogen atom contributes 1 valence electron. Since there are three hydrogen atoms, the total number of valence electrons in PH3 is 5 + 3 = 8.
Place the phosphorus atom (P) in the center and arrange the three hydrogen atoms (H) around it. Each hydrogen atom should be bonded to the phosphorus atom. Then, distribute the remaining valence electrons to satisfy the octet rule by forming lone pairs on the phosphorus atom. In this case, all three hydrogen atoms are bonded to the phosphorus atom, and there are two lone pairs on the phosphorus atom.
H
/
H-P-H
\
H
Step 2: Determine the electron pair arrangement (EPA):
To determine the EPA, consider both the bonding pairs and lone pairs around the central atom. In PH3, there are three bonding pairs and two lone pairs. This gives us a total of five electron pairs. According to the electron pair repulsion theory, these electron pairs will arrange themselves in a way that maximizes the distance between them.
Step 3: Determine the molecular geometry and bond angle:
With five electron pairs around the central phosphorus atom, the molecular geometry of PH3 is trigonal bipyramidal. The two lone pairs occupy equatorial positions, while the three hydrogen atoms are located in the axial positions.
The bond angle is the angle between two adjacent atoms or groups around the central atom. In the case of PH3, the bond angle between the three hydrogen atoms (H-P-H) is approximately 90 degrees. This is because the three hydrogen atoms are in the axial positions of the trigonal bipyramidal shape, which are perpendicular to the equatorial plane.
In summary, the shape of PH3 is trigonal bipyramidal, and the bond angle between the hydrogen atoms is approximately 90 degrees.