Lewis Structure of AlH3 (With 5 Simple Steps to Draw!)

Ready to learn how to draw the lewis structure of AlH3?

Awesome!

Here, I have explained 5 simple steps to draw the lewis dot structure of AlH3 (along with images).

So, if you are ready to go with these 5 simple steps, then let’s dive right into it!

Lewis structure of AlH3 contains three single bonds between the Aluminum (Al) atom and each Hydrogen (H) atom. The Aluminum atom (Al) is at the center and it is surrounded by 3 Hydrogen atoms (H).

Let’s draw and understand this lewis dot structure step by step.

(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of AlH3).

5 Steps to Draw the Lewis Structure of AlH3

Step #1: Calculate the total number of valence electrons

Here, the given molecule is AlH3. In order to draw the lewis structure of AlH3, first of all you have to find the total number of valence electrons present in the AlH3 molecule.
(Valence electrons are the number of electrons present in the outermost shell of an atom).

So, let’s calculate this first.

Calculation of valence electrons in AlH3

• For Aluminum: 

Aluminum is a group 13 element on the periodic table. ^[1]

Hence, the valence electrons present in aluminum is 3 (see below image).

• For Hydrogen: 

Hydrogen is a group 1 element on the periodic table. ^[2]

Hence, the valence electron present in hydrogen is 1 (see below image).

Hence in a AlH3 molecule, 

Valence electrons given by Aluminum (Al) atom = 3
Valence electrons given by each hydrogen (H) atom = 1
So, total number of Valence electrons in AlH3 molecule = 3 + 1(3) = 6

Step #2: Select the center atom (H is always outside)

While selecting the center atom, always put the least electronegative atom at the center.

(Remember: Fluorine is the most electronegative element on the periodic table and the electronegativity decreases as we move right to left in the periodic table as well as top to bottom in the periodic table). ^[1]

Here in the AlH3 molecule, if we compare the aluminum atom (Al) and hydrogen atom (H), then hydrogen is less electronegative than aluminum. But as per the rule, we have to keep hydrogen outside.

So, aluminum should be placed in the center and the remaining 3 hydrogen atoms will surround it.

Step #3: Put two electrons between the atoms to represent a chemical bond

Now in the above sketch of AlH3 molecule, put the two electrons (i.e electron pair) between each aluminum atom and hydrogen atom to represent a chemical bond between them.

These pairs of electrons present between the Aluminum (Al) and Hydrogen (H) atoms form a chemical bond, which bonds the aluminum and hydrogen atoms with each other in a AlH3 molecule.

Step #4: Complete the octet (or duplet) on outside atoms

In the Lewis structure of AlH3, the outer atoms are hydrogen atoms.

So now, you have to check whether these hydrogen atoms are forming a duplet or not! (because hydrogen requires only 2 electrons to have a complete outer shell).

You can see in the above image that all the hydrogen atoms form a duplet.

Also, all the 6 valence electrons of AlH3 molecule (as calculated in step #1) are used in the above structure. So there are no remaining electron pairs.

Hence there is no change in the above sketch of AlH3.

Let’s move to the next step.

Step #5: Check the stability of lewis structure by calculating the formal charge on each atom

Now, you have come to the final step and here you have to check the formal charge on aluminum atom (Al) as well as each hydrogen atom (H).

For that, you need to remember the formula of formal charge;

Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2

• For Aluminum:
  Valence electrons = 3 (as it is in group 13)
  Nonbonding electrons = 0
  Bonding electrons = 6
• For Hydrogen:
  Valence electron = 1 (as it is in group 1)
  Nonbonding electrons = 0
  Bonding electrons = 2

Formal charge	=	Valence electrons	–	Nonbonding electrons	–	(Bonding electrons)/2
Al	=	3	–	0	–	6/2	=	0
H	=	1	–	0	–	2/2	=	0

So you can see above that the formal charges on aluminum as well as hydrogen are “zero”.

Hence, there will not be any change in the above structure and the above lewis structure of AlH3 is the final stable structure only.

Each electron pair (:) in the lewis dot structure of AlH3 represents the single bond ( | ). So the above lewis dot structure of AlH3 can also be represented as shown below.

Related lewis structures for your practice:
Lewis Structure of MgF2
Lewis Structure of SbF3
Lewis Structure of Cl3-
Lewis Structure of PCl2-
Lewis Structure of AsO2- 

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