Element guide
Electron configuration of Technetium (Tc)
The electron configuration of Technetium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s2. In shorthand form it is written as [Kr] 4d5 5s2.
Use this page to connect the notation with atomic number 43, the d-block, and the valence pattern 4d5 5s2.
How to write the configuration
Configuration at a glance
Technetium has atomic number 43, so a neutral atom has 43 electrons. The configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s2 is a compact record of where those electrons sit by subshell.
The shorthand [Kr] 4d5 5s2 replaces the filled inner core with the previous noble gas. That notation keeps attention on the electrons that usually explain bonding, ions, and periodic trends.
Step-by-step filling
After the krypton core (36 electrons), 7 more electrons need placement. The 5s subshell receives 2 electrons, and 5 electrons go into the 4d subshell.
Step-by-step filling walkthrough: 1. Start with atomic number 43. 2. Fill through krypton: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 (36 electrons). 3. Fill 5s2 (38 electrons total). 4. Place 5 electrons in 4d (43 electrons total). 5. The 4d5 configuration has all five d orbitals singly occupied (Hund's rule), giving Tc five unpaired electrons.
Why the d5 s2 configuration matters
Technetium is an artificial element (it was the first element to be synthesized) and is radioactive. Its 4d5 5s2 configuration with a half-filled d-subshell makes it less reactive to further d-electron promotion than its neighbor Ruthenium. Unlike Molybdenum (group 6), Tc in group 7 does not promote an s electron to the d-subshell because the d5 arrangement is already half-filled.
Common mistakes
The first mistake is counting electrons incorrectly. After krypton (36), 5s2 (38), 4d5 (43). Verify: 2+2+6+2+6+10+2+6+5+2 = 43. The second mistake is forgetting that Tc is a synthetic element — its properties are less frequently tested, but its configuration follows standard Aufbau filling without exceptions.
A third common error is assuming Tc follows the same exception pattern as Mo or Cr. It does not — Tc has a stable d5 s2 configuration, not d6 s1.
Technetium reference table
| Item | Value |
|---|---|
| Atomic number | 43 |
| Full configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s2 |
| Noble-gas notation | [Kr] 4d5 5s2 |
| Valence clue | 4d5 5s2 |
| Block | d-block |
Use the table as a learning reference, then verify advanced oxidation-state questions with your course material.
Before you submit an answer
- The superscripts add up to 43 for a neutral Technetium atom.
- The notation follows the filling order used in your course.
- The last occupied subshell matches the periodic-table block.
- Any transition-metal or actinide exception is checked against a reference.
- The shorthand core is a noble gas, not a random previous element.
Common questions
What is the electron configuration of Technetium?
The neutral Technetium atom is written as 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s2. The shorthand form is [Kr] 4d5 5s2.
How many valence electrons does Technetium have?
Start from the outer-shell clue 4d5 5s2. For transition metals, inspect both s and d electrons carefully. Technetium has 7 valence electrons.
Is Technetium radioactive?
Yes, all isotopes of Technetium are radioactive. The most stable isotope, Tc-98, has a half-life of about 4.2 million years. It was the first artificially produced element.
Does Technetium have an Aufbau exception like Chromium?
No. Technetium follows the standard filling pattern, giving [Kr] 4d5 5s2 with a half-filled d-subshell. No electron promotion from 5s to 4d is needed.
Practice nearby concepts
Study notes and practice checks
From answer to understanding
Technetium sits in group 7 between Molybdenum and Ruthenium. Its 4d5 5s2 configuration gives it a half-filled d-subshell, which is inherently stable. This is why, unlike Mo, Tc does not show an s-to-d electron promotion.
Practice comparison
Compare Technetium (Tc) with Manganese (Mn) and Rhenium (Re). Mn: [Ar] 3d5 4s2, Tc: [Kr] 4d5 5s2, Re: [Xe] 4f14 5d5 6s2. All three group 7 elements have the d5 s2 configuration with no exceptions.
Teacher and self-study notes
Technetium is rarely covered in detail on general chemistry exams, but its configuration follows the clean d5 s2 pattern expected for group 7. The main point to remember is that it does NOT follow the Mo/Cr exception pattern.
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