Technetium (Tc): Bohr Model, Protons, Neutrons & Electrons
Technetium is element number 43, a transition metal in group 7, period 5. Its atom has 43 protons, 55 neutrons and 43 electrons arranged in 5 shells: 2, 8, 18, 13, 2.
Protons, neutrons and electrons in technetium
The atomic number of technetium is 43, so every technetium atom has 43 protons. A neutral atom has the same number of electrons, 43. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For technetium-98, that is 98 − 43 = 55 neutrons. Every isotope of technetium is radioactive; 98 is the mass number of its most stable one.
How to draw the Bohr model of technetium
- Draw the nucleus and write 43 p⁺ and 55 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 13 electrons on it.
- Draw the fifth shell and put 2 electrons on it.
- Check: 2 + 8 + 18 + 13 + 2 = 43 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, 13, 2) is the one to draw.
Electron configuration
The electron configuration of technetium is [Kr] 5s² 4d⁵. As a transition metal it fills an inner d-subshell, and its common ion is Tc⁴⁺.
Key facts about technetium
| Symbol | Tc |
|---|---|
| Atomic number | 43 |
| Relative atomic mass | [98] |
| Group · period · block | group 7 · period 5 · d-block |
| Type | Transition Metal |
| State at 25 °C | solid |
| Electron shells | 2, 8, 18, 13, 2 |
| Electron configuration | [Kr] 5s² 4d⁵ |
| Valence electrons | varies (outer shell: 2) |
| Common ion | Tc⁴⁺ |
| Electronegativity (Pauling) | 1.90 |
| First ionisation energy | 7.28 eV (702 kJ/mol) |
| Atomic radius (empirical) | 135 pm |
Where technetium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does technetium have?
Technetium has 43 protons and 43 electrons (atomic number 43). Its most common isotope, technetium-98, has 98 − 43 = 55 neutrons.
What is the electron configuration of technetium?
[Kr] 5s² 4d⁵. In shells that is 2, 8, 18, 13, 2.
How many valence electrons does technetium have?
Technetium is a transition metal, so its valence electrons are spread over two shells; its outermost shell holds 2.
Where is technetium on the periodic table?
In group 7, period 5, in the d-block. It is a transition metal.
