PH3 (Phosphine) Lewis Structure, Shape, Molecular Geometry
Phosphine is a very toxic gaseous compound. In phosphine (PH3) lewis structure, there are three sigma bonds and one lone-pair around phosphorous atom. No charges on phosphorous atom and hydrogen atoms. Shape of PH3 is trigonal pyramidal. Molecular geometry around phosphorous atom is tetrahedral. Total valence electrons pairs around phosphorous atom is four. In this tutorial we will learn how to draw the lewis structure of PH3 and determining the shape and molecular geometry of the molecule.
PH3 lewis structure
According to the lewis structure shown above, you will understand phosphine's structure is a simple. Therefore, we can draw the lewis structure of phosphine easily.
Steps of drawing lewis structure of PH3
There are several steps to draw the lewis structure of PH3. But, because phosphine is a simple molecule, these steps are not complex and do not require all general steps which are used to draw lewis structures of complex molecules and ions. Those steps are explained in detail in this tutorial.
- Find total number of electrons of the valance shells of hydrogen atoms and phosphorous atom
- Total electrons pairs as lone pairs and bonds
- Center atom selection
- Mark lone pairs on atoms
- Mark charges on atoms if there are charges on atoms.
- Check the stability and minimize charges on atoms by converting lone pairs to bonds to obtain best lewis structure.
Total number of electrons of the valance shells of PH3
There are two elements in PH3; hydrogen and phosphorous. Hydrogen is a group IA element and has only one electron in its last shell (valence shell). Phosphorus is a group VA element in the periodic table and contains five electrons in its last shell. Now we know how many electrons are includes in valence shells of hydrogen and phosphorus atom.
To find out total valence electrons given by a particular element, you should multiply number of electrons of the valance shell by the number of atoms of that element.
- valence electrons given by hydrogen atoms = 1 * 3 = 3
- valence electrons given by phosphorus atom = 5*1 = 5
- Total valence electrons = 3 + 5 = 8
Total valence electrons pairs
Total valance electrons pairs = σ bonds + π bonds + lone pairs at valence shells
Total electron pairs are determined by dividing the number total valence electrons by two. For, PH3, Total pairs of electrons are 4.
Center atom of PH3 molecule
To be the center atom, ability of having greater valance is important. Then, from hydrogen and phosphorus, which atom has the highest valence? Maximum valence of phosphorus is five. Hydrogen's only valence is one. Therefore, phosphrus atom should be the center atom of PH3. Now, we can draw the sketch of PH3 to describe how atoms are attached with each other.
Mark lone pairs on atoms
After determining the center atom and sketch of PH3 molecule, we can start to mark lone pairs on atoms. Remember that, there are total of four electron pairs.
- There are already three P-H bonds in the above drawn sketch. Now only one (4-3) electron pair remains to mark on atoms.
- Usually, those remaining electron pairs should be started to mark on outside atoms. But in PH3, hydrogen atom are the outside atoms which cannot keep more than two electron in its last shell. There are already two electrons in hydrogen atoms. Therefore, we cannot mark that electrons pair on hydrogen atoms.
- Therefore, then mark that electron pair on center atom; phosphorus.
Mark charges on atoms
There are no charges on phosphorus atom and hydrogen atoms. Also, remember that PH3 is a molecule which does not have a overall charge.
Check the stability and minimize charges on atoms by converting lone pairs to bonds
Because there is no charges on atoms, no need to reduce charges as a step of obtaining the best lewis structure. So, we have got the best lewis structure for PH3.
Shape and Geometry of phosphine
There are three sigma bonds and one lone-pair around phosphorus atom . Therefore, shape of PH3 is trigonal pyramidal.
Summation of number of sigma bonds and lone-pairs around phosphorus atom is four. Therefore geometry should be tetrahedral.
Questions
What are the similarities in lewis structures of ammonia and phosphine?
Both structures have three sigma bonds and one lone pair on center atom. So, shape of both ammonia and phosphine is trigonal pyramidal.
Are there charges on atoms in PH3 lewis structure?
There are no direct charges such as -1,+1 on atoms. But, due to electronegativity difference, phosphorus and hydrogen atoms are slightly polarized. Phosphorus is negatively polarized and hydrogen is positively polarized.