Thallium Lewis Structure

Thallium Lewis Structure: Tl Lewis Structure, see text Geometry, sp Hybridization & Polarity

Thallium Key Facts

The Thallium Lewis structure is central Tl bonded; the central Tl has 2 electron domains (1 lone pair), giving a linear electron-domain arrangement and a see text molecular geometry with a — bond angle. Tl is best described as sp-hybridized, and Thallium is polar because the see text shape (and/or unequal terminal atoms) prevents cancellation of the bond dipoles.

Figure 1: Lewis Structure of Thallium (Tl)

Chemical Formula	Tl
CAS Number	7440-28-0
Total Valence Electrons	3
Lewis Structure	central Tl bonded
Electron-Domain Geometry	linear
Molecular Geometry	see text
Hybridization Model	sp (central Tl)
Bond Angle	—
Polarity	Polar molecule

PubChem (CID 5359464) and NIST list Thallium as Tl with CAS 7440-28-0; molecular weight ≈ 204.383 g/mol. View CAS 7440-28-0 dictionary details on Guidechem →

Applications of Thallium (CAS 7440-28-0)

Thallium is encountered as a reagent, intermediate or specialty chemical in inorganic, organometallic and materials synthesis. Confirm grade, purity and supplier documentation (SDS) before specifying for a process.

Reagent / Intermediate Used in synthesis and formulation where the substance's reactivity is required.

Specialty Chemical Specified by grade for the intended process or research use.

Sourcing Verify purity, package and regional availability via the CAS identifier.

Procurement Note "Thallium" is supplied in multiple commercial grades and package sizes. Specify purity, grade, moisture/impurity limits, package (cylinder, drum or bulk) and intended process, and use CAS 7440-28-0 as the primary identifier when screening suppliers; always confirm regional availability and safety documentation (SDS).

Step 1 - Valence Electrons & Central Atom

To draw the Thallium Lewis structure we first count the total valence electrons. Tl contains 3 (Tl); the net charge of 0 gives a total of 3 valence electrons to place.

The central atom is Tl. It is the least electronegative atom capable of forming multiple bonds and is surrounded by the more electronegative terminal atom(s); hydrogen, when present, always occupies a terminal position. Electronegativity considerations place the electron density toward the terminal atom(s).

Valence-electron count

Total valence electrons = 3 (Tl) = 3 electrons.

Step 2 - Lewis Structure & Electron Distribution

Place Tl at the center and connect each surrounding atom with a single bond, complete octets on the terminal atoms, and place any remaining electrons on the central atom. The resulting electron distribution is: central Tl bonded; one lone pair on Tl and one unpaired electron on Tl.

Counting bonding and nonbonding electrons around Tl therefore satisfies the octet/expanded-octet requirement for the drawn structure.

Tl: 1 lone pair, 0 bonding domains

0 bonding domains + 1 lone pairs = 2 electron domains

Octet Rule: Why Tl Has Eight Electrons Tl forms 0 bond(s) and retains 2 nonbonding electron(s), reaching an octet. No expanded octet is required for this second-row (or octet-satisfying) central atom.

Step 3 - VSEPR Theory & Geometry

VSEPR theory states that the 2 electron domains around Tl arrange to minimize mutual repulsion, giving an linear electron-domain geometry.

Because 1 of these domains are lone pair(s) — and lone pairs repel more strongly than bonding pairs — the observed molecular geometry is see text; the Tl bond angle is set to — rather than the ideal value for the electron-domain geometry.

Repulsion hierarchy

A useful VSEPR approximation is: lone pair–lone pair repulsion > lone pair–bonding pair repulsion > bonding pair–bonding pair repulsion. With 1 lone pair(s) on Tl, the lone-pair domains occupy positions that minimize overall repulsion while pushing the bonding domains (and therefore the bonded atoms) closer together.

Hybridization & Formal Charge

In the conventional localized-bond model, Tl uses sp hybrid orbitals to form the 2 equivalent electron-domain directions (0 bonding + 1 lone pair).

Formal-charge check

Formal charge on central Tl = V − N − ½B = 3 − 2 − ½×0 = 1. The nonzero formal charge is distributed by resonance / charge separation; the drawn structure is the lowest-energy contributor.

Modeling Note Modeling Note: sp is a compact model for the 2 electron-domain directions around Tl; full quantum-chemical treatments use molecular orbitals.

Is Thallium Polar or Nonpolar?

Thallium is polar. The see text shape prevents cancellation of the bond dipoles. The bond dipoles do not cancel, leaving a net molecular dipole, which strongly influences solvation behavior and intermolecular interactions.

Expert Quote — Structural Chemistry Perspective

The decisive structural fact is not simply that the individual bonds are polar; it is whether molecular symmetry allows their vector sum to vanish. In Thallium the see text arrangement prevents cancellation, so a permanent dipole remains.

Interpretation consistent with standard VSEPR / molecular-geometry references.

This polarity profile underpins its behavior as a solvent, reactant or process intermediate; when sourcing, specify grade and container compatibility.

Structural Comparison Table

Species	Formula	Central Atom	Electron Domains	Molecular Geometry	Polarity
Thallium	Tl	Tl	2	see text	Polar
Carbon dioxide	CO₂	C	2	linear	Nonpolar
Carbon monoxide	CO	C	2	linear (diatomic)	Polar
Carbon disulfide	CS₂	C	2	linear	Nonpolar

Practice question Starting from the 3 valence electrons of Tl, draw the Lewis structure and confirm the central Tl atom is sp-hybridized with see text geometry. What happens to the bond angle if one terminal atom is replaced by a more electronegative substituent?

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FAQs

Is Tl polar or nonpolar?

Thallium is polar. Its see text geometry (and/or unequal terminal atoms) stops the bond dipoles from cancelling.

What is the Lewis structure of Thallium?

central Tl bonded; one lone pair on Tl and one unpaired electron on Tl. It uses all 3 valence electrons and the preferred structure carries a formal charge of 1 on the central atom.

What is the bond angle in Thallium?

The Tl angle is about —. Lone-pair repulsion compresses the angle from the ideal linear value.

What is the hybridization of Tl in Thallium?

The conventional model is sp. Thallium has 2 electron domains around the central Tl.

What is the CAS number of Thallium?

The CAS number is 7440-28-0. PubChem (CID 5359464) and NIST identify this with Tl; use it to locate suppliers and database records.

References

PubChem CID 5359464, Thallium. Molecular formula, CAS number, molecular weight and chemical identity.
NIST Chemistry WebBook, SRD 69, Thallium. Formula, CAS Registry Number and thermochemical / spectroscopic data.
IUPAC Gold Book. Definitions for "lone pair", "VSEPR", "hybridization" and "formal charge".
Atkins, P. & de Paula, J., Physical Chemistry. VSEPR, molecular geometry and dipole moments.
Guidechem supplier & dictionary records. Commercial sourcing and CAS-linked property pages for Thallium (CAS 7440-28-0).

Technical scope: Lewis structures, VSEPR and hybridization are model-based descriptions for chemical communication and structure prediction; actual molecular electronic structure is more accurately represented by molecular-orbital and quantum-chemical methods. Commercial grades vary substantially by supplier and intended use; CAS 7440-28-0 identifies the substance, not a universal purity specification.

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Thallium Lewis Structure