Lewis structure of PH₃
8 valence electrons. Three P-H single bonds, with one lone pair on P.
Lewis structure
8 valence electronsFormal charges: none
Why this shape
- P has 5 valence electrons. It uses three in three single bonds to H, so two are left as one lone pair.
- Steric number = three sigma bonds + one lone pair = 4, so P is sp³ hybridised.
- Four electron pairs point to the corners of a tetrahedron (tetrahedral electron geometry). With one lone pair in place of atoms, the atoms make a trigonal pyramidal shape.
- P is larger and less electronegative than N, so the bond pairs sit farther from P and repel less. The angle closes to about 93.5 degrees, much less than 107 in NH3.
- The bond dipoles do not cancel in the trigonal pyramidal shape, so PH₃ is polar.
How to draw it
- Count the valence electrons: P 5 + 3 × H 1 = 8 valence electrons, 4 pairs.
- Put P in the middle and join it to the three outer atoms with single bonds.
- Give each outer atom lone pairs until it has an octet (H needs only two electrons), then put any electrons left over on the central atom.
- Result: three P-H single bonds, with one lone pair on P.
- Formal charge = valence electrons − lone pair electrons − number of bonds. Here: none.
Class 11, Chapter 4 Chemical Bonding and Molecular Structure.
Lewis structure of PH3: quick answers
How many valence electrons are in PH3?
P 5 + 3 × H 1 = 8 valence electrons, 4 pairs.
What are the formal charges in the Lewis structure of PH3?
Every atom has a formal charge of zero.
How many lone pairs are in the Lewis structure of PH3?
1 in all, 1 of them on the central P.