Erbium (Er): Bohr Model, Protons, Neutrons & Electrons
Erbium is element number 68, a lanthanide in the f-block (the lanthanide row drawn below the table), period 6. Its atom has 68 protons, 98 neutrons and 68 electrons arranged in 6 shells: 2, 8, 18, 30, 8, 2.
Protons, neutrons and electrons in erbium
The atomic number of erbium is 68, so every erbium atom has 68 protons. A neutral atom has the same number of electrons, 68. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For erbium-166, that is 166 − 68 = 98 neutrons. Erbium has 6 stable isotopes, with 94, 96, 98, 99, 100, 102 neutrons.
How to draw the Bohr model of erbium
- Draw the nucleus and write 68 p⁺ and 98 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 30 electrons on it.
- Draw the fifth shell and put 8 electrons on it.
- Draw the sixth shell and put 2 electrons on it.
- Check: 2 + 8 + 18 + 30 + 8 + 2 = 68 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, 30, 8, 2) is the one to draw.
Electron configuration
The electron configuration of erbium is [Xe] 6s² 4f¹². As a lanthanide it fills an inner f-subshell, and its common ion is Er³⁺.
Key facts about erbium
| Symbol | Er |
|---|---|
| Atomic number | 68 |
| Relative atomic mass | 167.26 |
| Group · period · block | f-block · period 6 |
| Type | Lanthanide |
| State at 25 °C | solid |
| Electron shells | 2, 8, 18, 30, 8, 2 |
| Electron configuration | [Xe] 6s² 4f¹² |
| Valence electrons | varies (outer shell: 2) |
| Common ion | Er³⁺ |
| Electronegativity (Pauling) | 1.24 |
| First ionisation energy | 6.11 eV (590 kJ/mol) |
| Atomic radius (empirical) | 175 pm |
Where erbium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does erbium have?
Erbium has 68 protons and 68 electrons (atomic number 68). Its most common isotope, erbium-166, has 166 − 68 = 98 neutrons.
What is the electron configuration of erbium?
[Xe] 6s² 4f¹². In shells that is 2, 8, 18, 30, 8, 2.
How many valence electrons does erbium have?
Erbium is a lanthanide, so its valence electrons are spread over two shells; its outermost shell holds 2.
Where is erbium 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.
