Which Electron Configuration Matches This Model?
Which electron configuration matches this model? The answer depends on what the model shows: a Bohr-style atom with electron shells, a diagram containing orbitals and arrows, a Lewis symbol, or a more detailed energy-level arrangement. The central task is always the same—count the electrons in the model, determine how they are distributed among shells or subshells, and write the corresponding electron configuration. Understanding the difference between shell notation and subshell notation prevents many common mistakes Not complicated — just consistent..
Understanding the Different Atomic Models
An atomic model is a visual representation of an atom. Different models underline different information, so each one corresponds to a slightly different form of electron configuration Small thing, real impact..
The Bohr Model
The Bohr model, also called the shell model, places electrons in numbered energy levels or shells. The first shell can hold 2 electrons, the second can hold 8, the third can hold 18, and each additional shell can hold up to 32 electrons in principle Practical, not theoretical..
A Bohr model for phosphorus might show:
- 2 electrons in the first shell
- 8 electrons in the second shell
- 5 electrons in the third shell
Its shell configuration is therefore:
2, 8, 5
The total number of electrons is 15, identifying the atom as phosphorus.
The Aufbau or Energy-Level Model
An energy-level diagram shows the order in which subshells fill. The typical filling order is:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d
The Aufbau principle means that electrons occupy the available orbital with the lowest energy before occupying one with a higher energy That alone is useful..
A model showing 11 electrons would match:
1s² 2s² 2p⁶ 3s¹
This is the ground-state electron configuration of sodium And it works..
The Orbital-Box Model
An orbital-box diagram uses boxes to represent orbitals and arrows to represent electrons Easy to understand, harder to ignore..
For example:
- One box labeled 1s containing one up-and-down pair represents 1s²
- Three boxes labeled 2p, each containing an up-and-down pair, represent 2p⁶
- Three boxes labeled 3p, each containing one upward arrow, represent 3p³
According to Hund’s rule, electrons occupy the three orbitals of a p subshell individually before they begin to pair. According to the Pauli exclusion principle, no orbital can contain more than two electrons, and those two electrons must have opposite spins.
The Lewis Model
A Lewis structure or Lewis symbol shows only the valence electrons around an element symbol. It does not display the complete electron configuration.
Here's one way to look at it: sodium is represented as:
Na·
This indicates one valence electron. Its full configuration is:
1s² 2s² 2p⁶ 3s¹
Therefore
