Thulium (Tm)
Thulium is element 69, a lanthanide in the lanthanide series (period 6). A neutral atom has 69 protons, 100 neutrons and 69 electrons, 2 of them valence electrons.
Lanthanide- Atomic number
- 69
- Atomic mass
- 168.93 u
- Valence electrons
- 2*
- Protons · neutrons
- 69 · 100
- Electrons per shell
- 2, 8, 18, 31, 8, 2
- At room temperature
- solid
Bohr model of thulium
The Bohr model draws thulium as a nucleus of 69 protons and 100 neutrons, with its 69 electrons on 6 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 31 in shell 4, 8 in shell 5, 2 in shell 6. Press Build the atom to watch the shells fill from the inside out. The outer ring (the P shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of thulium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹³
Short form (noble gas notation): [Xe] 6s² 4f¹³. The [Xe] stands for the electrons of xenon, the noble gas before it.
How many valence electrons does thulium have?
Thulium has 2 valence electrons.
Thulium is a lanthanide, so its valence electrons are less clear-cut than for main-group elements. It has 2 electrons in its outermost shell (shell 6), and electrons in its inner f and d subshell can also take part in bonding.
Protons, neutrons and electrons
| Protons | 69 | equal to the atomic number |
|---|---|---|
| Electrons | 69 | equal to the protons in a neutral atom |
| Neutrons | 100 | mass number 169 − 69 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Thulium properties
| Symbol | Tm |
|---|---|
| Category | Lanthanide |
| Group · period · block | — · 6 · f |
| Atomic mass | 168.93 u |
| State at 25 °C | solid |
| Melting point | 1,818 K (1,540 °C, 2,810 °F) |
| Boiling point | 2,223 K (1,950 °C, 3,540 °F) |
| Density | 9.32 g/cm³ |
| Electronegativity (Pauling) | 1.25 |
| Atomic radius | 227 pm |
| First ionization energy | 6.184 eV |
| Electron affinity | — |
| Oxidation states | +3 |
| Common ion charge | +3 |
| Discovered | 1879 by Per Teodor Cleve |
Where thulium sits on the periodic table
Lanthanides: Lanthanum, Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Gadolinium.
Questions about thulium
How many valence electrons does thulium have?
Thulium has 2 valence electrons in its outer shell; inner d or f electrons can also bond.
How many protons, neutrons and electrons does thulium have?
A neutral thulium atom has 69 protons and 69 electrons. Its most common form has about 100 neutrons (mass number 169 − 69 protons).
What is the electron configuration of thulium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹³, written in short form as [Xe] 6s² 4f¹³.
What does the Bohr model of thulium look like?
A nucleus of 69 protons and 100 neutrons, circled by 6 electron shells holding 2, 8, 18, 31, 8, 2 electrons.
What is the atomic number of thulium?
69. The atomic number is the number of protons in the nucleus, and it is what makes an atom thulium.