Ibr3 Lewis Structure, Characteristics: 13 Facts You Should Know

Ibr3 is a polyatomic molecule comprising of one iodine atom and three bromine atoms with molar mass 366.62 g/mol. Let us study some more facts and details of Ibr3 lewis structure.

Ibr3 (iodine tribromide), is an interhalogen compound with two different halogens bonded together and is dark brown in color. It is produced by reacting atomic bromine with Ibr2 with elemental bromine gas at an elevated temperature and used as flame retardant.

Ibr3 is an interhalogen compound formed by heavy elements and it is quite difficult to synthesize at moderate temperatures. Let us discuss more detail oriented facts like valence electrons, lone pairs and characteristics like shape, hybridization of Ibr3 lewis structure.

How to draw Ibr3 Lewis structure?

Ibr3 lewis structure is drawn by following octet rule to give an idea about the skeletal structure of Ibr3. Let us construct the following steps required.

Counting total valence electrons

Ibr3 has a total of 28 valence electrons for constructing Ibr3 lewis structure. It has four 17th group elements (I and 3 Br) meaning each atom has 7 valence electrons (outermost electrons) in the atomic orbitals. Group 17, the halogen group, has valence shell electronic configuration as: ns2np5.

Choosing the central atom

The least electronegative atom, I, with X= 2.66 is taken as the central atom in lewis structure and Br (X=2.96) is placed as the surrounding atoms. The electronegative atoms are compared in terms of their magnitude. Br is more electronegative as conveyed by X value (X= electronegativity difference magnitude).

Construction of skeletal structure

Each Br atom has two electrons shared with I atom, counting a total of 6 valence electrons used for 3 Br atoms. The remaining electrons are arranged around the atoms but I expands its octet to accommodate 10 electrons violating the octet rule. It can accommodate extra electrons due to the extra subshell.

Formation of bonds

In this step, the pair of electrons shared between atoms are drawn in the form of bonds. 3 single bonds are formed between 3 sets of I-Br. The remaining valence electrons reside as lone pairs of electrons on the respective atoms.

IBr3 Lewis structure

Ibr3 lewis structure resonance

Resonance structures or canonical structures is a representation of the delocalization of bonds/electrons in a molecule. Let us check if Ibr3 lewis structure has resonance forms.

Ibr3 lewis structure has no resonance structure. This is because all single bonds and fixed lone pairs of electrons has no delocalization of electron cloud.

Ibr3 has neither ionic nor covalent canonical forms.

Ibr3 hybridization

Ibr3 lewis structure has sp3d hybridization that can be easily calculated using VSEPR theory. Let us discuss the mathematical formulation for hybridization.

Hybridization of a Ibr3 = (Valence electrons of the central atom + Number of monovalent atoms attached to the central atom + Negative charge on the molecule – Positive charge on the molecule)/2

  • Hybridization of Ibr3= (7+3-0)/2
  • Hybridization of Ibr3= 5 = sp3d
  • Hybridization of Ibr3= sp3d
  • Molecular geometry based on sp3d hybridization is trigonal bipyramidal (TBP).
  • Electronegative atoms occupy axial positions as it has more p character following Drago’s rule.

Why and how Ibr3 is sp3d hybridized ?

It doesn’t take up square pyramidal geometry as the five electron groups are not identical and they are further separated by electronegativity difference.

Ibr3 is sp3d hybridized as it involves five electron groups, out of which one two are lone pairs and three are bond pairs and takes up TBP geometry. The two lone pairs of I occupy the equatorial positions and the more electronegative Br atoms occupy both the axial positions and one equatorial positions.

sp3d hybridization of Ibr3 lewis structure

Ibr3 lewis structure shape

The shape of a molecule depends on two different factors; bonding and non-bonding electron pairs. Let us understand how.

The shape of Ibr3 lewis structure is T-shaped structure. This is due to the 3 Br atoms occupying the two axial positions and one equatorial positions. Shape of a molecule is determined by the bonding pairs.

Orbitals of lone pairs of electrons are not accounted to describe the shape of any molecule.

T-shaped geometry of Ibr3 lewis structure

Ibr3 valence electrons

The valence electrons is the outermost electrons in atomic orbitals present. Let us calculate the total valence electrons.

The total valence electrons of Ibr3 is 28. The ground state electronic configuration of I and Br are: [Kr]4d105s25p5 and [Ar]3d104s24p5. Each atom has 7 valence electrons in its outermost shell.

The 4d and 3d shells of I and Br are completely filled and inert. They are not valence shells as the prefix of d differs from s and p.

Ibr3 lewis structure lone pairs

Lone pairs of electrons are the electrons that do not participate in hybridization. Let us calculate the lone pairs of Ibr3.

The total lone pairs of electrons of Ibr3 lewis structure is 11. Each Br has 3 lone pairs which makes a total of 9 lone pairs residing on 3 Br atoms and I contains 2 lone pairs. They are localized on their respective atoms and cannot show delocalization of electron cloud.

Ibr3 lewis structure angle

Ibr3 lewis structure adopts sp3d hybridization meaning it has two different angles. Let us discuss it below.

The bond angles of Ibr3 with Trigonal Bipyramidal geometry with sp3d hybridization are 1200 and 900 for equatorial and axial positions. The axial bonds suffer more repulsion and hence, has longer bond lengths as it should be since it possesses more p character.

The lone pairs therefore occupies 1200 bond angle for minimum repulsion.

The two Br atoms in axial positions have a bond angle of 1800 with the central I atom and the angle between one axial Br, central I and one equatorial Br atoms is 900.

Ibr3 lewis structure octet rule

Octet rule implies that every atoms tries to accommodate 8 electrons in their subshells for noble and inert characteristics. Let us check if Ibr3 follows octet rule.

In Ibr3, I does not follow octet rule due to its expanded subshells bearing 10 electrons. Br follows octet rule as it has a total of 8 electrons in its surrounding. Most elements down the group have extra subshells due to its large size and violates the octet rule if necessary.

Ibr3 lewis structure formal charge

Formal charge is the hypothetical charge acquired if all the electrons are shared equally in the molecule. Let us calculate formal charge for Ibr3.

Formal charge = (Number of valence electrons in a free atom of the element) – (Number of unshared electrons on the atom) – (Number of bonds to the atom).

Is Ibr3 polar or non-polar?                        

Ibr3 is a polar molecule. Let us discuss in details.

Ibr3 has T-shaped structure with asymmetric electron cloud distribution on I. The dipole moments of Ibr3 do not cancel each other completely due to I-Br X difference.           

Polarity of a molecule can be well known from its dipole moments vectors and their orientation which depends on electronegativity difference, presence of lone pairs etc. X= magnitude of electronegativity difference.

Is Ibr3 ionic or covalent?

Ibr3 is a covalent compound based on Fajan’s rule. Let us discuss in details.

The electronegativity difference of I and Br is negligible. It also do not possess any electronic charge separation and are formed by two non-metals. This makes Ibr3 lewis structure a covalent compound.

Why Ibr3 is covalent ?

Ibr3 is covalent because electronegativity difference between two non-metals, I and Br, is 0.30 and to be ionic, it should have been greater than 1.7. The size of the cation, I3+ and size of the anion, Br are comparable in size with less polarizing power.

Ibr3 electron geometry

Electron geometry of Ibr3 lewis structure is trigonal bipyramidal. Let us check for Ibr3.

Ibr3 lewis structure has three single bonds meaning 3 electron groups plus two non-bonded electron pairs on central atom (I). It has a total of 5 electron groups so the electron geometry is trigonal bipyramidal (TBP).

How electron geometry is TBP ?

Molecular geometry and electron geometry are two different ways of representing a molecule and molecular geometry depends only on the bonded electron pairs.

The electron geometry of Ibr3 is TBP due to the arrangement of electron groups and it includes bonded, non-bonded electron pairs. Ibr3 has 5 electron groups with different ligands, belonging to TBP geometry.

Ibr3 oxidation state

Oxidation state is the hypothetical static charge of an atom in a molecule formed by loss or gain of electrons. Let us calculate the oxidation state of ibr3.

I has an oxidation state of +3 and each Br atom has -1 charge. As Br is more electronegative than I, each Br takes up one electron from I so I loses 3 electrons. As each Br takes one electron from I, it has -1 charge due to gain of an extra electron.

Gaining of electrons means reduction and it gives negative charge as electron has a negative charge.


Ibr3 lewis structure is a T-shaped interhalogen molecule with trigonal bipyramidal geometry. It has 3 single bonds and a total of 11 lone pairs of electrons.

Nandita Biswas

Hello. I am doing my Masters in Chemistry with a specialization in organic and physical chemistry. Also, I have done two projects in chemistry- One dealing with colorimetric estimation and determination of ions in solutions. Others in Solvatochromism study of fluorophores and their uses in the field of chemistry alongside their stacking properties on emission. I have also specialized in Resin chemicals. Let's connect through LinkedIn-https://www.linkedin.com/in/nandita-biswas-244b4b179

Recent Posts