Electron Cloud Shells and Orbitals Marked on Periodic Table of Atoms
Electron Cloud Shells: The Foundation of Atomic Structure
The electron cloud refers to the region surrounding the nucleus where electrons are likely to be found. These electrons are organized into shells, each representing a specific energy level.
Here is Periodic Table for Atoms, with marked Electroun Cloud Shells and Orbitals. Under this table is explanation, how it works

1. Energy Levels and Quantum Numbers
- Principal Quantum Number (n): The energy levels, or shells, are denoted by the principal quantum number n, where
n = 1, 2, 3, ...
. - Each shell corresponds to a spherical region around the nucleus, with larger n values representing shells farther from the nucleus.
- Example: For
n = 1
, electrons are closest to the nucleus; forn = 2
, they occupy a larger spherical region.
2. Subshells and Orbital Shapes
Within each energy shell, electrons are further organized into subshells:
- Subshells are labeled as s, p, d, and f, which describe the shape and distribution of electrons in the cloud.
- The s subshell is spherical, while other subshells have more complex shapes (e.g., dumbbell-shaped for p orbitals).
Shell (n) | Subshells | Total Orbitals | Max Electrons |
---|---|---|---|
1 | 1s | 1 | 2 |
2 | 2s, 2p | 4 | 8 |
3 | 3s, 3p, 3d | 9 | 18 |
4 | 4s, 4p, 4d, 4f | 16 | 32 |
Orbital Shapes
Here is an image showing the shapes of atomic orbitals:
- s orbitals → Spherical shape
- p orbitals → Dumbbell shape (along x, y, and z axes)
- d orbitals → More complex, with cloverleaf and donut-like shapes
- f orbitals → Even more intricate shapes

3. Shell Sizes and Radii
- Radius and Distance from Nucleus: Shell size increases with n, meaning higher shells are farther from the nucleus.
- Shielding Effect: Electrons in inner shells partially block the nuclear charge for outer-shell electrons, reducing their attraction to the nucleus.
4. Electron Capacity
Formula for Maximum Electrons:
- Each shell can hold
2n2
electrons. For example: n = 1
:2(12) = 2
electronsn = 2
:2(22) = 8
electronsn = 3
:2(32) = 18
electrons
5. Electron Distribution, Stability and Filling Order
- Principles of Filling Order of Shells: Electrons fill shells and subshells in a specific order, dictated by the Aufbau principle (lower energy orbitals fill first).
- Order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p
- Image of Filling Order: is marked in table below
- Octet Rule: Atoms tend to fill their outermost shell (valence shell) with 8 electrons for stability, forming the basis for chemical bonding.
Filling order of shells in table
6. Applications of Electron Shells
- Spectral Lines: Electrons jumping between shells emit or absorb energy as light, producing unique spectral lines for each element.
- Chemical Reactivity: The number and arrangement of electrons in the outermost shell determine an atom's reactivity and bonding behavior.
- Periodic Trends: Properties like atomic radius, ionization energy, and electronegativity depend on electron shells and their distribution.
Links to connected topics

6. Applications of Electron Shells
- Spectral Lines: Electrons jumping between shells emit or absorb energy as light, producing unique spectral lines for each element.
- Chemical Reactivity: The number and arrangement of electrons in the outermost shell determine an atom's reactivity and bonding behavior.
- Periodic Trends: Properties like atomic radius, ionization energy, and electronegativity depend on electron shells and their distribution.
Links to connected topics
https://en.wikipedia.org/wiki/Island_of_stability
https://en.wikipedia.org/wiki/Quantum_tunnelling