Thallium (Tl)

Silvery white

Thallium is a soft, malleable post-Transition known for its extreme toxicity, and with [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹, thallium mimics potassium in biological systems, disrupting ion channels. Historically used as a rat poison and in electronics, its applications are now tightly controlled due to severe health risks.

Key metrics

Density11.85g/cm³

Melting point577K

Boiling point1,746K

Electronegativity1.62Pauling

Discovery

1861discovered

Discovered by: William Crookes
Reactivity profile: Toxic and moderately reactive
Reactivity: Medium
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Xe]}\; \textcolor{#a855f7}{4_{f}^{14}}\; \textcolor{#22c55e}{5_{d}^{10}}\; \textcolor{#ef4444}{6_{s}^{2}}\; \textcolor{#3b82f6}{6_{p}^{1}}

[Xe] 4f14 5d10 6s2 6p1

Wave function

\Psi_{\text{Tl}} \approx \frac{1}{\sqrt{81!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{81}(\mathbf{r}_{81}) \right|

Probability density $|\Psi|^2$ across the Tl valence shell.

Crystal structure

Hexagonal Close-Packed

Lattice constantsa 1.00 · b 1.00 · c 1.63

Cell anglesα 90° · β 90° · γ 120°

Coordination number12

Atoms per cell2

Atomic packing factor0.74

Physical properties

Atomic radius: 156 pm
Ionization energy: 589 kJ/mol
Electron affinity: 19 kJ/mol
Crystal structure: Hexagonal close-packed (hcp)

Oxidation states

+1+3

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

577 K1746 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

377.6nmTl I (UV)UV60%

530.7nmTl IGreen50%

535.0nmTl I (green)Green100%

Dominant line 535.0 nmRange 378–535 nmTransitions 3