Electron Configuration and Orbital Diagrams: Study Notes

Electrons in Atoms and the Periodic Table

Electron Orbital Diagrams

Electron orbital diagrams visually represent the arrangement of electrons within atomic orbitals. These diagrams help illustrate how electrons fill available orbitals according to specific rules.

• Degenerate orbitals: Orbitals in the same sublevel (e.g., all three 2p orbitals) have the same energy.

• Hund's Rule: Electrons occupy degenerate orbitals singly with parallel spins before pairing up. This minimizes electron-electron repulsion and stabilizes the atom.

Type of Orbital	Number of Orbitals	Maximum Electrons
s	1	2
p	3	6
d	5	10
f	7	14

• Example: For an atom with 8 electrons, the orbital diagram fills as follows: 1s2 2s2 2p4.

Practice: Identifying violations of Hund's Rule involves checking if electrons are paired in degenerate orbitals before all are singly occupied.

Ground State Electron Configuration

The ground state electron configuration describes the lowest energy arrangement of electrons in an atom. Electrons fill orbitals in order of increasing energy, following the Aufbau Principle.

• Aufbau Principle: Electrons fill the lowest energy orbitals first, starting with 1s, then 2s, 2p, 3s, etc.

• Pauli Exclusion Principle: Each orbital can hold a maximum of two electrons with opposite spins.

Example: Fluorine (Z = 9): Electron configuration: 1s2 2s2 2p5

• Practice: Identifying violations of the Aufbau Principle involves checking if electrons are placed in higher energy orbitals before lower ones are filled.

Identifying Elements from Electron Configurations

Given an electron configuration or orbital diagram, you can identify the corresponding element by counting the total number of electrons (equal to the atomic number for a neutral atom).

• Example: 1s2 2s2 2p6 3s2 3p2 corresponds to Silicon (Si), atomic number 14.

Writing Electron Configurations and Orbital Diagrams

To write the electron configuration and orbital diagram for an element:

1. Determine the atomic number (number of electrons).

2. Fill orbitals in order of increasing energy using the Aufbau Principle.

3. Apply Hund's Rule and the Pauli Exclusion Principle as you fill each sublevel.

• Example: Sulfur (Z = 16): Electron configuration: 1s2 2s2 2p6 3s2 3p4

• Example: Magnesium (Z = 12): Electron configuration: 1s2 2s2 2p6 3s2

Unpaired vs. Paired Electrons

Definition and Identification

Electrons in an orbital can be either paired (two electrons with opposite spins) or unpaired (a single electron in an orbital). The number of unpaired electrons affects the magnetic properties of an atom.

• Unpaired Electron: An electron occupying an orbital alone (e.g., one electron in a p orbital).

• Paired Electrons: Two electrons occupying the same orbital with opposite spins.

Type	Orbital Diagram
Unpaired	↑
Paired	↑↓

• Example: Vanadium (V) has 3 unpaired electrons in its ground state configuration.

Practice: Determining the number of unpaired electrons in a given element helps predict its magnetic behavior (paramagnetic if unpaired, diamagnetic if all paired).

Summary Table: Electron Filling Order

Order of Filling	Sublevel
1	1s
2	2s
3	2p
4	3s
5	3p
6	4s
7	3d
8	4p
...	...

Additional info: The order of filling is determined by increasing energy, which can be remembered using the diagonal rule or by consulting an Aufbau diagram.