Element guide
Electron configuration of Cadmium (Cd)
The electron configuration of Cadmium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2. In shorthand form it is written as [Kr] 4d10 5s2.
Use this page to connect the notation with atomic number 48, the d-block, and the valence pattern 4d10 5s2.
How to write the configuration
Configuration at a glance
Cadmium has atomic number 48, so a neutral atom has 48 electrons. The configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 shows a completely filled 4d subshell and a filled 5s subshell.
The shorthand [Kr] 4d10 5s2 replaces the filled inner core with the previous noble gas. For Cadmium, the 4d10 subshell is part of the valence description, along with 5s2.
Step-by-step filling
After the krypton core (36 electrons), 12 more electrons need placement. The 5s subshell receives 2 electrons (5s2), and the 4d subshell fills completely with 10 electrons (4d10).
Step-by-step filling walkthrough: 1. Start with atomic number 48. 2. Fill through krypton: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 (36 electrons). 3. Fill 5s2 (38 electrons total). 4. Fill 4d10 (48 electrons total). 5. The 4d10 subshell is completely filled, making Cd diamagnetic.
The post-exception configuration
Cadmium comes immediately after Palladium (which has the extreme [Kr] 4d10 configuration with no 5s electrons). Cd restores the expected 5s2 pattern. The filled 4d10 and 5s2 give Cd a stable closed-shell configuration similar to group 12 elements (Zn, Hg).
Like zinc, Cd commonly forms Cd2+ by losing the two 5s electrons, leaving a filled 4d10 core.
Common mistakes
The first mistake is carrying over the Pd exception pattern to Cd. Unlike Pd, Cd has a normal 5s2 configuration. The second mistake is miscounting: 2+2+6+2+6+10+2+6+10+2 = 48.
A third common error is writing the 4d and 5s order incorrectly. While 5s fills before 4d in the Aufbau sequence, the final notation places 4d before 5s by principal quantum number order.
Cadmium reference table
| Item | Value |
|---|---|
| Atomic number | 48 |
| Full configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 |
| Noble-gas notation | [Kr] 4d10 5s2 |
| Valence clue | 4d10 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 48 for a neutral Cadmium 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 Cadmium?
The neutral Cadmium atom is written as 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2. The shorthand form is [Kr] 4d10 5s2.
Does Cadmium have any Aufbau exceptions?
No, Cadmium follows the standard filling pattern. Its configuration [Kr] 4d10 5s2 is exactly what you would predict from the Aufbau principle.
How many valence electrons does Cadmium have?
Cadmium has 2 valence electrons in the 5s subshell. The 4d10 electrons are sometimes considered part of the core, though they participate in some coordination chemistry.
Why is Cadmium toxic?
Cadmium's toxicity is related to its chemical similarity to zinc. Cd2+ can replace Zn2+ in essential enzymes and proteins, disrupting their function.
Practice nearby concepts
Study notes and practice checks
From answer to understanding
Cadmium completes the period 5 transition series as a group 12 element. Its noble-gas-like d10 s2 configuration makes it chemically similar to Zinc and Mercury.
Practice comparison
Compare Cadmium (Cd) with Zinc (Zn) and Mercury (Hg). Zn: [Ar] 3d10 4s2, Cd: [Kr] 4d10 5s2, Hg: [Xe] 4f14 5d10 6s2. All three group 12 elements have the d10 s2 configuration, though Hg shows relativistic effects that affect its chemistry.
Teacher and self-study notes
Cadmium is a good example of the post-transition region. After the extensive Aufbau exceptions in period 5 (Nb through Pd), Cd reverts to the expected filling pattern. This makes it a useful configuration to contrast with its neighbor Palladium.
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