Lutetium (Lu): Bohr Model, Protons, Neutrons & Electrons
Lutetium is element number 71, a lanthanide in the f-block (the lanthanide row drawn below the table), period 6. Its atom has 71 protons, 104 neutrons and 71 electrons arranged in 6 shells: 2, 8, 18, 32, 9, 2.
Protons, neutrons and electrons in lutetium
The atomic number of lutetium is 71, so every lutetium atom has 71 protons. A neutral atom has the same number of electrons, 71. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For lutetium-175, that is 175 − 71 = 104 neutrons. Lutetium has 2 stable isotopes, with 104, 105 neutrons.
How to draw the Bohr model of lutetium
- Draw the nucleus and write 71 p⁺ and 104 n⁰ inside it.
- Draw the first shell and put 2 electrons on it (the first shell holds at most 2).
- Draw the second shell and put 8 electrons on it.
- Draw the third shell and put 18 electrons on it.
- Draw the fourth shell and put 32 electrons on it.
- Draw the fifth shell and put 9 electrons on it.
- Draw the sixth shell and put 2 electrons on it.
- Check: 2 + 8 + 18 + 32 + 9 + 2 = 71 electrons, the same as the number of protons.
From potassium onwards the shells don’t simply fill as 2, 8, 8: the fourth shell starts before the third is full, so the real arrangement above (2, 8, 18, 32, 9, 2) is the one to draw.
Electron configuration
The electron configuration of lutetium is [Xe] 6s² 4f¹⁴ 5d¹. As a lanthanide it fills an inner f-subshell, and its common ion is Lu³⁺.
Key facts about lutetium
| Symbol | Lu |
|---|---|
| Atomic number | 71 |
| Relative atomic mass | 174.97 |
| Group · period · block | f-block · period 6 |
| Type | Lanthanide |
| State at 25 °C | solid |
| Electron shells | 2, 8, 18, 32, 9, 2 |
| Electron configuration | [Xe] 6s² 4f¹⁴ 5d¹ |
| Valence electrons | varies (outer shell: 2) |
| Common ion | Lu³⁺ |
| Electronegativity (Pauling) | 1.27 |
| First ionisation energy | 5.43 eV (524 kJ/mol) |
| Atomic radius (empirical) | 175 pm |
Where lutetium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does lutetium have?
Lutetium has 71 protons and 71 electrons (atomic number 71). Its most common isotope, lutetium-175, has 175 − 71 = 104 neutrons.
What is the electron configuration of lutetium?
[Xe] 6s² 4f¹⁴ 5d¹. In shells that is 2, 8, 18, 32, 9, 2.
How many valence electrons does lutetium have?
Lutetium is a lanthanide, so its valence electrons are spread over two shells; its outermost shell holds 2.
Where is lutetium on the periodic table?
In the f-block (the lanthanide row drawn below the table), period 6, in the f-block. It is a lanthanide.
