Element 81 · Thallium (Tl)

Thallium Bohr model: diagram and electrons per shell

The thallium Bohr model shows a thallium atom (Tl) as a small nucleus with its electrons circling it in 6 shells: 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O and 3 in shell P. This page has a rotating 3D thallium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the thallium Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of thallium (Tl), a simplified picture of a single thallium atom. Its nucleus holds 81 protons, and a neutral thallium atom has 81 electrons, arranged around it in 6 shells (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O and 3 in shell P).

Tl K · 21s² L · 82s² 2p⁶ M · 183s² 3p⁶ 3d¹⁰ N · 324s² 4p⁶ 4d¹⁰ 4f¹⁴ O · 185s² 5p⁶ 5d¹⁰ P · 36s² 6p¹

Thallium Bohr model diagram

Bohr model diagram of thallium: a nucleus of 81 protons with 81 electrons on 6 shells, 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O and 3 in shell P, each ring labelled with its shell letter. — The thallium Bohr model drawn flat: each ring is a shell, labelled with its letter, and every dot is an electron (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O and 3 in shell P).

Thallium electrons per shell

A neutral thallium atom has 81 electrons, one for each of its 81 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O and 3 in shell P.

Electrons in each shell of the thallium Bohr model
Shell	Shell number (n)	Electrons	Most it can hold (2n²)	Subshells
K	1	2	2	1s²
L	2	8	8	2s² 2p⁶
M	3	18	18	3s² 3p⁶ 3d¹⁰
N	4	32	32	4s² 4p⁶ 4d¹⁰ 4f¹⁴
O	5	18	50	5s² 5p⁶ 5d¹⁰
P	6	3	72	6s² 6p¹

How the thallium Bohr model builds up, shell by shell

Watch the thallium Bohr model come together: the nucleus first, then each shell in turn, from the innermost outwards, with its electrons joining the ring. The legend names every shell and counts its electrons, so you can read off the arrangement (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O and 3 in shell P) as it forms.

Animation of the thallium Bohr model being built: a nucleus of 81 protons appears first, then each shell grows in around it and takes its electrons, giving 81 electrons on 6 shells (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O and 3 in shell P). — The thallium Bohr model built up in six seconds: the nucleus first, then each shell with its electrons, ending with 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O and 3 in shell P. Protons are red, neutrons yellow and electrons blue.

How to draw the thallium Bohr model

Find the atomic number. Thallium has atomic number 81, so a neutral atom has 81 protons and 81 electrons.
Draw the nucleus. Put a circle in the centre and write Tl in it. The 81 protons sit there with the neutrons.
Draw the shells. Sketch 6 shells as rings around the nucleus. A shell holds at most 2n² electrons: 2 in the first, 8 in the second, 18 in the third and 32 in the fourth.
Place the electrons. Fill from the inside out: 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O and 3 in shell P.
Check the total. 2 + 8 + 18 + 32 + 18 + 3 = 81, the atomic number, so every electron is accounted for.

Atomic data for the thallium Bohr model

The numbers behind the thallium Bohr model, grouped by topic. Radii are in picometres (pm) and energies in kilojoules per mole (kJ/mol).

Identity

Symbol: Tl
Atomic number: 81
Atomic mass: 204.38 u
Family: Post-Transition Metals
Position: group 13, period 6
Block: p-block

Electron configuration

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p¹
Shorthand: [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹
Electrons per shell: 2, 8, 18, 32, 18, 3
Outer-shell electrons: 3 in shell P

Ionisation energies

I₁: 589.4
I₂: 1971
I₃: 2878

Energy to remove each electron in turn (kJ/mol). A sharp jump means the next electron comes from an inner shell.

Atomic radii

Calculated (pm): 156
Empirical (pm): 190
Covalent (pm): 144
Van der Waals (pm): 196

Electronegativity and electron affinity

Electronegativity (Pauling): 1.62
Electron affinity (kJ/mol): 36.4

Oxidation states

+1 +3

Charges the element commonly takes in compounds.

Physical properties, abundance and history of thallium

Bulk properties of thallium, how common it is, who discovered it and some of its compounds.

Physical properties

Phase at room conditions: Solid
Appearance: Silvery white
Melting point: 303.85°C (577 K)
Boiling point: 1472.85°C (1746 K)
Density: 11.85 g/cm³
Thermal conductivity (W/m·K): 46.1
Specific heat (J/g·K): 0.129
Molar heat capacity (J/mol·K): 26.32
Heat of fusion (kJ/mol): 4.31
Heat of vaporisation (kJ/mol): 162.4

Abundance

Earth's crust (mg/kg): 0.85
Oceans (mg/L): 0

Discovery

Discovered by: William Crookes
Year: 1861

Common compounds

thallium(I) acetate C2H3O2Tl
Thallous nitrate NO3Tl
Thallium monochloride ClTl
Thallium Tl
Thallous Chloride Tl-201 ClTl
Thallium bromide BrTl
Cyclopentadienylthallium C5H5Tl
Ethanol, thallium(1+) salt C2H5OTl

Compounds listed in the PubChem database.

Main isotopes of thallium

Isotopes of thallium share the same 81 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of thallium: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
200	–	26.1 h	β⁺
201	–	3.042 d	EC
202	–	12.31 d	EC
203	29.515 %	stable	–
204	–	3.783 y	β⁻, EC + β⁺
205	70.485 %	stable	–

α = alpha decay, β⁻ = beta-minus, β⁺ = beta-plus, EC = electron capture, SF = spontaneous fission, p / n = proton / neutron emission.

More about thallium

Thallium on the periodic table – properties, isotopes, uses and the full thallium page.
Post-Transition Metals – all post-transition metal elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.