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Atomic diagrams consist of a simplified representation of the electronic configuration of an atom by layers or energy levels. They are a very simple way to see the valence shell of an element as well as the number of electrons present in the inner shells, which is useful for predicting the physical and chemical properties of an element.

## How are atomic diagrams constructed?

The construction of atomic diagrams is based on the electronic configuration of the element. It is a relatively simple process that is carried out in the same way for each atom in the periodic table. The process is the following:

### Step #1: Write the electronic configuration of the element

The electronic configuration is obtained using the rule of rain and the total number of electrons of the atom in question. If it is a neutral atom, the number of electrons matches the atomic number of the element. If, on the other hand, it is an ion, the number of electrons is calculated as the atomic number minus the electrical charge of the ion (including its sign if it is negative). That is, the following formula is used:

Once the number of electrons is obtained, they are distributed among the different sublevels of the atom, filling the ones with the lowest energy first until they are completely filled before moving on to the next orbital or sublevel. The order of filling is determined by the Madelung rule, also known as the rain rule, and is schematized in the following figure:

That is, the filling is done according to the sum of n+l, instead of only considering n. The list of all the subshells with the maximum number of electrons that can fit in each one, following this filling rule, is:

1s ^{2} |
2s ^{2} |
2p ^{6} |
3s ^{2} |
3p ^{6} |
4s ^{2} |
3d ^{10} |
4p ^{6} |
5s ^{2} |
4d ^{10} |
5p ^{6} |
6s ^{2} |
4f ^{14} |
5d ^{10} |
6p ^{6} |
7s ^{2} |
5f ^{14} |
6d ^{10} |
7p ^{6} |

There are more sublevels, but no element in the periodic table manages to locate electrons in them.

### Step #2: Group the orbitals in order of increasing energy level

The filling of the orbitals following the method of the rain does not always produce the electronic configuration ordered by principal energy level. For this reason, after filling in the subshells, they must be grouped by their non-principal quantum number value.

### Step #3: Add up the electrons in each energy level to get the electron shell configuration

Once the final electronic configuration is obtained, we add the number of electrons in all the orbitals present in each level. In this way, what is known as the electronic configuration by levels or by layers is obtained. Each main energy level (ie, each value of n) is identified with a capital letter of the alphabet, beginning with the letter K, as indicated in the following table:

no |
Layer |
number of e ^{–} |

1 | k | maximum 2 |

2 | L | maximum 8 |

3 | m | maximum 18 |

4 | No. | maximum 32 |

5 | EITHER | maximum 50 |

6 | P | maximum 72 |

7 | Q | maximum 98 |

The maximum number of electrons is placed as a reference to verify that there was no error in the counting or distribution of electrons. An atom can have less than the maximum in its last electronic shells, but it can never have more than that number.

### Step #4: Make a diagram with as many concentric circles as the period in which the element is

By having the layered configuration we are ready to build the atomic diagram. Just draw a series of concentric circles around the atomic nucleus. A circle must be drawn for each shell that contains electrons. Thus, if the shell configuration of an atom is K ^{2} L ^{5} , then two circles must be drawn, one for the K shell (n=1) and one for the L shell (n=2). The number of electronic layers of an element coincides with the period in which it is located on the periodic table.

### Step #5: Starting with the smallest circumference (n=1), distribute the electrons in each energy level until they are all exhausted

Finally, a small circle is drawn on each of these circumferences for each electron that contains the respective shell. In the previous example, (K ^{2} L ^{5} ) we must place two electrons in the first circle and 5 in the second. Every effort should be made to distribute the electrons as evenly as possible.

## Examples of the construction of atomic diagrams of the elements

### Hydrogen (H, Z=1)

Number of electrons: 1

Electronic configuration (rain method): 1s ^{1}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{1} |
k | 1 |

Layered electron configuration: K ^{1}

Number of occupied layers: 1

Atomic diagram of hydrogen:

### Oxygen (O, Z=8)

Number of electrons: 8

Electron configuration (rain method): 1s ^{2} 2s ^{2} 2p ^{4}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{2} |
k | 2 |

2 | 2s ^{2} 2p ^{4} |
L | 6 |

Electron configuration by layers: K ^{2} L ^{6}

Number of occupied layers: 2 (two concentric circles)

Oxygen atomic diagram:

### Sodium (Na, Z=11)

Number of electrons: 11

Electron configuration (rain method): 1s ^{2} 2s ^{2} 2p ^{6} 3s ^{1}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{2} |
k | 2 |

2 | 2s ^{2} 2p ^{6} |
L | 8 |

3 | 3s ^{1} |
m | 1 |

Electron configuration by layers: K ^{2} L ^{8} M ^{1}

Number of occupied layers: 3 (three concentric circles)

Sodium atomic diagram:

### Aluminum (Al, Z=13)

Number of electrons: 13

Electron configuration (rain method): 1s ^{2} 2s ^{2} 2p ^{6} 3s ^{2} 3p ^{1}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{2} |
k | 2 |

2 | 2s ^{2} 2p ^{6} |
L | 8 |

3 | 3s ^{2} 3p ^{1} |
m | 3 |

Electron configuration by layers: K ^{2} L ^{8} M ^{3}

Number of occupied layers: 3 (three concentric circles)

Atomic diagram of aluminum:

### Phosphorus (P, Z=15)

Number of electrons: 15

Electron configuration (rain method): 1s ^{2} 2s ^{2} 2p ^{6} 3s ^{2} 3p ^{3}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{2} |
k | 2 |

2 | 2s ^{2} 2p ^{6} |
L | 8 |

3 | 3s ^{2} 3p ^{3} |
m | 5 |

Electron configuration by layers: K ^{2} L ^{8} M ^{5}

Number of occupied layers: 3 (three concentric circles)

Phosphorus atomic diagram:

### Calcium (Ca, Z=20)

Number of electrons: 20

Electron configuration (rain method): 1s ^{2} 2s ^{2} 2p ^{6} 3s ^{2} 3p ^{6} 4s ^{2}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{2} |
k | 2 |

2 | 2s ^{2} 2p ^{6} |
L | 8 |

3 | 3s ^{2} 3p ^{6} |
m | 8 |

4 | 4s ^{2} |
No. | 2 |

Layered electron configuration: K ^{2} L ^{8} M ^{8} N ^{2}

Number of occupied layers: 4 (four concentric circles)

Calcium atomic diagram:

### Zinc (Zn, Z=30)

Number of electrons: 30

Electron configuration (rain method): 1s ^{2} 2s ^{2} 2p ^{6} 3s ^{2} 3p ^{6} 4s ^{2} 3d ^{10}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{2} |
k | 2 |

2 | 2s ^{2} 2p ^{6} |
L | 8 |

3 | 3s ^{2} 3p ^{6} 3d ^{10} |
m | 18 |

4 | 4s ^{2} |
No. | 2 |

Layered electron configuration: K ^{2} L ^{8} M ^{18} N ^{2}

Number of occupied layers: 4 (four concentric circles)

Atomic diagram of zinc:

### Germanium (Ge, Z=32)

Number of electrons: 32

Electron configuration (rain method): 1s ^{2} 2s ^{2} 2p ^{6} 3s ^{2} 3p ^{6} 4s ^{2} 3d ^{10} 4p ^{2}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{2} |
k | 2 |

2 | 2s ^{2} 2p ^{6} |
L | 8 |

3 | 3s ^{2} 3p ^{6} 3d ^{10} |
m | 18 |

4 | 4s ^{2} 4p ^{2}^{} |
No. | 4 |

Electron configuration by layers: K ^{2} L ^{8} M ^{18} N ^{4}

Number of occupied layers: 4 (four concentric circles)

Germanium atomic diagram:

### Bromine (Br, Z=35)

Number of electrons: 35

Electron configuration (rain method): 1s ^{2} 2s ^{2} 2p ^{6} 3s ^{2} 3p ^{6} 4s ^{2} 3d ^{10} 4p ^{5}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{2} |
k | 2 |

2 | 2s ^{2} 2p ^{6} |
L | 8 |

3 | 3s ^{2} 3p ^{6} 3d ^{10} |
m | 18 |

4 | 4s ^{2} 4p ^{5}^{} |
No. | 7 |

Electron configuration by layers: K ^{2} L ^{8} M ^{18} N ^{7}

Number of occupied layers: 4 (four concentric circles)

Bromine atomic diagram:

### Xenon (Xe, Z=54)

Number of electrons: 54

^{Electron configuration} (rain method): 1s ^{2} 2s ^{2} 2p ^{6 3s }^{2} 3p ^{6} 4s ^{2} 3d ^{10} 4p ^{6} 5s ^{2} 4d 10 ^{5p} 6^{}^{}^{}^{}^{}^{}

Total number of electrons per shell:

no |
sublevels |
Layer |
number of e ^{–} |

1 | 1s ^{2} |
k | 2 |

2 | 2s ^{2} 2p ^{6} |
L | 8 |

3 | 3s ^{2} 3p ^{6} 3d ^{10} |
m | 18 |

4 | 4s ^{2} 4p ^{6} 4d ^{10} |
No. | 18 |

5 | 5s ^{2} 5p ^{6} |
EITHER | 8 |

Electron configuration by layers: K ^{2} L ^{8} M ^{18} N ^{18} O ^{8}

Number of occupied layers: 5 (five concentric circles)

Xenon atomic diagram:

## References

Chang, R., & Goldsby, K. (2013). *Chemistry* (11th ed.). McGraw-Hill Interamericana de España SL

Miguel, J. (2020, July 14). *Representation of the atom from the atomic number and the mass number using the planetary model* . SpaceScience.com. https://espaciociencia.com/representacion-del-atomo/

Montagud Rubio, N. (2022, February 15). *Moeller diagram: what it is, how it is used in Chemistry, and examples* . Psychology and Mind. https://psicologiaymente.com/miscelanea/diagrama-moeller

Prototypes, C. L. (nd). *Parts of an Atomic Diagram Activity* . Storyboard That. https://www.storyboardthat.com/es/lesson-plans/ensenanza-de-los-atomos/partes-del-%c3%a1tomo