AsH3 Lewis structure

AsH₃ (arsine) has one arsenic atom and three hydrogen atoms.

In the AsH₃ Lewis structure, three single bonds around the arsenic atom, with three hydrogen atoms attached to it, and on the arsenic atom, there is one lone pair.

Alternative method: Lewis structure of AsH₃

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, arsenic lies in group 15, and hydrogen lies in group 1.

Hence, arsenic has five valence electrons and hydrogen has one valence electron.

Since AsH₃ has one arsenic atom and three hydrogen atoms, so…

Valence electrons of one arsenic atom = 5 × 1 = 5
Valence electrons of three hydrogen atoms = 1 × 3 = 3

And the total valence electrons = 5 + 3 = 8

Learn how to find: Arsenic valence electrons and Hydrogen valence electrons

• Second, find the total electron pairs

We have a total of 8 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 8 ÷ 2 = 4

• Third, determine the central atom

Here hydrogen can not be the central atom. Because the central atom is bonded with at least two other atoms, and hydrogen has only one electron in its last shell, so it can not make more than one bond.

Hence, here we have to assume that the central atom is arsenic.

Therefore, place arsenic in the center and hydrogens on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 4 electron pairs. And three As — H bonds are already marked. So we have to only mark the remaining one electron pair as a lone pair on the sketch.

Also remember that arsenic is a period 4 element, so it can keep more than 8 electrons in its last shell. And hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are hydrogens. But no need to mark on hydrogen, because each hydrogen has already two electrons.

So for arsenic, there is one lone pair.

Mark the lone pair on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For arsenic atom, formal charge = 5 – 2 – ½ (6) = 0

For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0

Here, both arsenic and hydrogen atoms do not have charges, so no need to mark the charges.

Final structure

The final structure of AsH₃ features a central arsenic atom connected to three hydrogen atoms through single covalent bonds. In this arrangement, the arsenic atom satisfies the octet rule by forming three bonding pairs and maintaining one lone pair. Each hydrogen atom reaches its stable duet state through its single shared bond. This configuration is the most stable because it results in formal charges of zero for all atoms involved, representing the most energetically favorable state for the molecule. Thus, this specific electronic distribution serves as the definitive and most accurate Lewis representation of arsine.

Next: SeF₆ Lewis structure

External video

• ASH3 Lewis Structure: How to Draw the Lewis Dot Structure for Arsenic Trihydride – YouTube • Wayne Breslyn

External links

• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/AsH3-lewis-structure.html
• https://techiescientist.com/ash3-lewis-structure/
• https://sciedutut.com/ash3-lewis-structure/