Calculator Input
Example Data Table
| Species | Atomic Number | Charge | Electron Count | Configuration | Shells |
|---|---|---|---|---|---|
| Hydrogen | 1 | 0 | 1 | 1s1 | K=1 |
| Sodium | 11 | 0 | 11 | 1s2 2s2 2p6 3s1 | K=2, L=8, M=1 |
| Iron | 26 | 0 | 26 | [Ar] 4s2 3d6 | K=2, L=8, M=14, N=2 |
| Copper | 29 | 0 | 29 | [Ar] 4s1 3d10 | K=2, L=8, M=18, N=1 |
| Calcium Ion | 20 | 2+ | 18 | [Ar] | K=2, L=8, M=8 |
| Bromide Ion | 35 | 1- | 36 | [Kr] | K=2, L=8, M=18, N=8 |
Formula Used
1) Electron count
Total electrons = Atomic number − Ionic charge
For a positive charge, electrons are removed. For a negative charge, electrons are added.
2) Subshell capacity
Capacity = 2(2l + 1)
This gives s = 2, p = 6, d = 10, and f = 14 electrons.
3) Filling order
The calculator follows the Madelung approach, using increasing n + l. When two subshells share the same n + l, the lower n fills first.
Typical order:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p
Known observed exceptions such as Cr, Cu, Nb, Mo, Pd, Pt, Au, and several f-block cases are included.
4) Cation removal rule
For positive ions, electrons are removed from the highest principal shell first. That is why transition-metal cations lose ns electrons before (n−1)d electrons.
How to Use This Calculator
- Enter the atomic number of the element.
- Add the ionic charge. Use 0 for a neutral atom.
- Choose whether to display full notation, shorthand notation, or both.
- Optionally enable neutral comparison and the detailed subshell table.
- Press Calculate Configuration to view the result above the form.
- Review shell distribution, block, period, last occupied subshell, and estimated unpaired electrons.
- Use the export buttons to download the result as CSV or PDF.
FAQs
1) What does electronic configuration mean?
It describes how electrons occupy shells and subshells around the nucleus. The arrangement helps explain reactivity, bonding behavior, magnetism, and periodic trends.
2) Why do some elements break the expected filling order?
A few atoms gain extra stability from half-filled or fully filled d and f subshells. Chromium and copper are classic examples.
3) Why are 4s electrons removed before 3d electrons in many cations?
Once a transition metal is ionized, the highest principal shell is usually removed first. That makes 4s electrons leave before 3d electrons.
4) What is noble-gas shorthand notation?
It replaces the filled inner configuration with the nearest earlier noble gas in brackets. This makes long configurations easier to read.
5) What does the shell graph show?
The graph groups electrons by principal shell, from K to Q. It gives a quick visual view of where electrons are concentrated.
6) Is the outer-shell electron count always the valence count?
Not always. For many main-group elements it works well, but transition metals can also involve nearby d electrons in chemical behavior.
7) Can this calculator handle ions?
Yes. Enter a positive charge for cations or a negative charge for anions. The tool adjusts electron count and updates the configuration.
8) Does this replace experimental spectroscopy?
No. It gives a strong rule-based estimate for learning and general chemistry work. Spectroscopic measurements remain the reference for detailed electronic structure.