Scandium (Sc): Bohr Model, Protons, Neutrons & Electrons
Scandium is element number 21, a transition metal in group 3, period 4. Its atom has 21 protons, 24 neutrons and 21 electrons arranged in 4 shells: 2, 8, 9, 2.
Protons, neutrons and electrons in scandium
The atomic number of scandium is 21, so every scandium atom has 21 protons. A neutral atom has the same number of electrons, 21. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For scandium-45, that is 45 − 21 = 24 neutrons.
How to draw the Bohr model of scandium
- Draw the nucleus and write 21 p⁺ and 24 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 9 electrons on it.
- Draw the fourth shell and put 2 electrons on it.
- Check: 2 + 8 + 9 + 2 = 21 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, 9, 2) is the one to draw.
Electron configuration
The electron configuration of scandium is [Ar] 4s² 3d¹. As a transition metal it fills an inner d-subshell, and its common ion is Sc³⁺.
Key facts about scandium
| Symbol | Sc |
|---|---|
| Atomic number | 21 |
| Relative atomic mass | 44.956 |
| Group · period · block | group 3 · period 4 · d-block |
| Type | Transition Metal |
| State at 25 °C | solid |
| Electron shells | 2, 8, 9, 2 |
| Electron configuration | [Ar] 4s² 3d¹ |
| Valence electrons | varies (outer shell: 2) |
| Common ion | Sc³⁺ |
| Electronegativity (Pauling) | 1.36 |
| First ionisation energy | 6.56 eV (633 kJ/mol) |
| Atomic radius (empirical) | 160 pm |
Where scandium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does scandium have?
Scandium has 21 protons and 21 electrons (atomic number 21). Its most common isotope, scandium-45, has 45 − 21 = 24 neutrons.
What is the electron configuration of scandium?
[Ar] 4s² 3d¹. In shells that is 2, 8, 9, 2.
How many valence electrons does scandium have?
Scandium is a transition metal, so its valence electrons are spread over two shells; its outermost shell holds 2.
Where is scandium on the periodic table?
In group 3, period 4, in the d-block. It is a transition metal.
