Thallium
POST-TRANSITION METAL
Bohr Model: Electrons arranged in energy shells around the nucleus.
Thallium is a chemical element with symbol Tl and atomic number 81. This soft gray post-transition metal is not found free in nature. When isolated, it resembles tin, but discolors when exposed to air.
Quick Facts
Atomic Number 81
Period 6
Group 13
Phase Solid
Appearance silvery white
About Post-Transition Metals
Transition metals are elements with partially filled d-orbitals. They are hard, have high melting points, and often form colored compounds.
History
Discovered By William Crookes
Named By Unknown
Physical Properties
Atomic Mass 204.38
Density 11.85 g/L
Molar Heat 26.32 J/(mol·K)
Phase Transition (Melting & Boiling Points)
Thallium melts at 577 K and boils at 1746 K.
Atomic Properties
Electron Config [Xe] 4f14 5d10 6s2 6p1
Electronegativity 1.62
Electron Affinity 36.4 kJ/mol
Ionization Energy 589.4 kJ/mol
Orbital Filling Diagram
This diagram visualizes electron configuration according to the Aufbau principle and Hund's rule.
Boxes represent orbitals (s, p, d, f), while arrows indicate electrons with spin up or down.
Electrons fill lower energy levels first and occupy orbitals singly before pairing.
Photograph
External Resources
Study Guide
Atomic Number
The number of protons in the nucleus, which defines the element.
Atomic Mass
The average mass of an atom, including protons and neutrons.
Electronegativity
A measure of how strongly an atom attracts electrons in a bond.
Ionization Energy
The energy required to remove an electron from an atom.
Electron Config
The arrangement of electrons in the atom's energy shells.