Recognised as Chemical element
Thallium
- Tl
- Z = 81
- post-transition metal
Thallium (Tl) is element 81, a post-transition metal in period 6 and group 13. Its standard atomic weight is 204.38 Da. Weights follow IUPAC standard atomic weights, 2021 revision.
Identity
SymbolTl
Standard atomic weight204.38atomic mass units (Da)
Mass in kilograms3.3938097 × 10^-25
Categorypost-transition metal
Group13
Period6
Blockp-block
Electrons in a neutral atom81
Neutrons in the most common isotope123≈
Electron configuration
Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p¹ground state, subshells written in order of n
Noble gas shorthand[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹
Electrons per shell2, 8, 18, 32, 18, 3K, L, M and outward
Electrons in the outer shell3
Unpaired electrons1Hund's rule; unpaired electrons make the free atom paramagnetic
Madelung ruleFollowedthe ground state is what the n + l filling order predicts
Quantities
Molar mass204.38 g/mol
Mass of one mole204.38 grams
Atoms in one gram2.9465411 × 10^21
Mass of one atom3.3938097 × 10^-22 g
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