The electronic configuration of an atom is a numerical representation of its electron orbitals. Electron orbitals are regions around the nucleus of an atom that have different shapes and in which electrons are mathematically likely to be located. Electron configuration can tell a reader quickly and simply how many orbitals an atom has, as well as how many electrons are in each orbital. After understanding the basic principles behind electron configuration, you will be able to write your own configurations and confidently tackle those Chemistry exams.
Steps
Method 1 of 4: Review
Step 1. What is an electron configuration?
An electron configuration shows the distribution of electrons in an atom or a molecule. There is a specific notation that can quickly show where electrons are likely to be. Therefore, knowing this notation is an essential part of knowing electron configurations. Reading these notations can tell you which element you are referring to and how many electrons it has.
 The structure of the periodic table is based on electron configuration.

For example, the notation for the phosphor (P) is 1s22s22p63s23p3 { displaystyle 1s ^ {2} 2s ^ {2} 2p ^ {6} 3s ^ {2} 3p ^ {3}}
Step 2. What are electronic layers?
The area around the nucleus of an atom, or the area where electrons orbit, is known as the electronic shell. There are usually about 3 electronic layers in each atom, and the arrangement of these is known as the electronic configuration. All electrons in the same shell must have the same energy.
Electronic shells are sometimes also called energy levels
Step 3. What is an atomic orbital?
As an atom acquires electrons, they fill different sets of orbitals in a specific order. When each set of orbitals is filled, it contains an even number of electrons. These are the sets of orbitals:
 The set of s orbitals (any number in the electron configuration followed by an "s") contains a single orbital and, according to the Pauli exclusion principle, a single orbital can contain at most 2 electrons. Hence, each set of s orbitals can have 2 electrons.
 The set of p orbitals contains 3 orbitals and therefore can have 6 electrons in all.
 The set of d orbitals contains 5 orbitals and can therefore have 10 electrons.
 The set of orbitals f contains 7 orbitals and, therefore, can have 14 electrons.
 The sets of g, h, i, and k orbitals are theoretical. No atom is known to have electrons in these orbitals. The set g has 9 orbitals and therefore could theoretically contain 18 electrons. Set h would have 11 orbitals and 22 electrons at most, set i would have 13 orbitals and 26 electrons at most, and set k would have 15 orbitals and 30 electrons at most.
 Remember the order of the letters in the first four sets using this mnemonic: Sor Pto Dand Fideos.
Step 4. What are overlapping orbitals?
Sometimes electrons occupy a shared space of orbitals. Consider the molecule of dihydrogen, or H2. The two electrons must stay close to each other to maintain attraction between them and connect. Because they are so close, they will occupy the same orbital space and thus will either share the orbital or overlap.

In the notation, you just change the row number to one less than it actually is. For example, the electron configuration of germanium (Ge) is 1s22s22p63s23p64s23d104p2 { displaystyle 1s ^ {2} 2s ^ {2} 2p ^ {6} 3s ^ {2} 3p ^ {6} 4s ^ {2} 3d ^ {10 } 4p 2}
Step 5. How do you use an electron configuration table?
If you have difficulty visualizing the notation, it may help to use an electron configuration table so that you can actually see what you are writing. Lay out a basic table with the energy levels along the yaxis and the type of orbital in the horizontal direction on the xaxis. From there, you can plot the notation in the corresponding spaces as they move along the yaxis and horizontally along the xaxis. Then you can follow the line to get the notation.

For example, if you were to write the beryllium configuration, you would start with 1s and then go back to 2s. Beryllium only has 4 electrons, so you would stop after this and have 1s22s2 { displaystyle 1s ^ {2} 2s ^ {2}}
Método 2 de 4: Asignar electrones con una tabla periódica
Step 1. Find the atomic number of the atom
Each atom has a specific number of electrons that is associated with it. Locate the chemical symbol for the atom on the periodic table. The atomic number is a positive integer starting from 1 (for hydrogen) and increasing by 1 with each subsequent atom. The atomic number of the atom is the number of protons in the atom and, therefore, in an atom whose charge is 0, it is also the number of electrons.
The periodic table is based on electron configuration, so you can use it to determine the notation for the configuration of the element
Step 2. Determine the charge of the atom
Uncharged atoms will have the exact number of electrons listed on the periodic table. However, charged atoms (ions) will have a greater or lesser number of electrons depending on the magnitude of the charge. If you are working with a charged atom, add or subtract electrons accordingly: add one electron for each negative charge and subtract one for each positive charge.
 For example, in the case of a sodium atom that has a charge of +1, one electron would be subtracted from its basic atomic number of 11. So the sodium atom would have 10 electrons in all.
 In the case of a sodium atom that has a charge of 1, one electron would be added to its basic atomic number of 11. So, the sodium atom would have 12 electrons in all.
Step 3. Understand electron configuration notation
The electron configurations are written in such a way as to clearly show the number of electrons in the atom and also in each orbital. Each orbital is written in sequence with the number of electrons in each in superscript to the right of the orbital's name. The final electron configuration constitutes a single series of orbital and superscript names.

For example, this is a simple electron configuration: 1s^{2} 2s^{2} 2 P^{6}.
This configuration shows that there are 2 electrons in the 1s set of orbitals, 2 electrons in the 2s set of orbitals, and 6 electrons in the 2p set of orbitals. 2 + 2 + 6 = 10 electrons in total. This electron configuration is for an uncharged atom of neon (the atomic number of neon is 10).
Step 4. Memorize the order of the orbitals
Note that the orbital sets are numbered according to the electronic shell but ordered in terms of energy. For example, a 4s^{2} full has less energy (or has a lower volatility potential) than a 3d^{10} partially full or full, so layer 4s is listed first. After knowing the order of the orbitals, you can just fill them according to the number of electrons the atom has. This is the order to fill the orbitals: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, 8s.
 The electron configuration of an atom that has all the orbitals completely filled would be written like this: 1s^{2} 2s^{2} 2 P^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{2} 4d^{10} 5 p^{6} 6s^{2} 4f^{14} 5 d^{10} 6p^{6} 7s^{2} 5f^{14} 6d^{10}7p^{6}
 Note that the above list, if all the layers were filled, would be the electron configuration of Og (oganeson), 118, the highest numbered atom on the periodic table. Therefore, this electronic configuration contains all the electronic shells that are currently known for an atom with a neutral charge.
Step 5. Fill the orbitals according to the number of electrons in the atom
For example, if you wanted to write the electron configuration of an uncharged calcium atom, you would start by looking up the atomic number on the periodic table. This is 20, so you will write a configuration for an atom that has 20 electrons in the order above.

Fill the orbitals in the order above until you reach 20 electrons in total. The 1s orbital contains 2 electrons, the 2s contains 2, the 2p contains 6, the 3s contains 2, the 3p contains 6, and the 4s contains 2 (2 + 2 + 6 +2 +6 + 2 = 20). Hence, the electron configuration of calcium is: 1s^{2} 2s^{2} 2 P^{6} 3s^{2} 3p^{6} 4s^{2}.
 Note: the energy level changes as you ascend. For example, when you are about to move to the fourth energy level, it becomes 4s first and later 3d. After the fourth energy level, you move on to the fifth, where the order is followed again (5s and then 4d). This only happens after the third energy level.
Step 6. Use the periodic table as a visual shortcut
You may have already observed that the shape of the periodic table corresponds to the order of the orbital sets in the electron configurations. For example, the atoms in the second column from the left always end in "s^{2}", the atoms at the far right of the central thin part always end in" d^{10}", etc. Use the periodic table as a visual guide for writing configurations. The order in which you add the electrons to the orbitals corresponds to the position in the table.
 Specifically, the two columns on the far left represent atoms that have electron configurations that end in s orbitals, the right block of the table represents atoms whose configurations end in p orbitals, the middle part represents atoms that end in d orbitals, and the bottom part represents the atoms that end in f orbitals.
 For example, when writing the electron configuration of chlorine, think of the following: "This atom is in the third row (or 'period') of the periodic table. It is also in the fifth column of the block of p orbitals of the table. Therefore, its electronic configuration will end in … 3p^{5}".
 Caution: the regions of the d and f orbitals in the table correspond to energy levels different from the period in which they are found. For example, the first row of the d orbital block corresponds to the 3d orbital although it is in period 4, while the first row of the f orbitals corresponds to the 4f orbital although it is in period 6.
Step 7. Learn shorthand for writing long electron configurations
The atoms along the right edge of the periodic table are known as Noble gases. These elements are very stable chemically. If you want to shorten the process of writing a long electron configuration, just enclose the chemical symbol for the closest noble gas that has fewer electrons than the atom you are working with in brackets, and then continue with the electron configuration for the next sets of orbitals..
 To understand this concept, it is helpful to write an example configuration. Write a configuration for zinc (atomic number 30) using noble gas shorthand. The complete electron configuration of zinc is: 1s^{2} 2s^{2} 2 P^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10}. However, note that 1s^{2} 2s^{2} 2 P^{6} 3s^{2} 3p^{6} it is the configuration of argon, a noble gas. Just replace this part of the electronic notation for zinc with the chemical symbol for argon in square brackets ([Ar]).
 So the electron configuration of zinc in shorthand is [Ar] 4s^{2} 3d^{10}.
 Note that if you are going to do the noble gas notation for argon, for example, it is not possible to write [Ar]. You must use the noble gas prior to that element. In the case of argon, it would be neon ([Ne]).
Method 3 of 4: Use an ADOMAH Periodic Table
Step 1. Understand the periodic table ADOMAH
This method of writing electronic configurations does not require memorization, but it does require a reorganized periodic table, since, in a traditional periodic table, starting from the fourth row, the period numbers do not correspond to the electronic shells. Look for an ADOMAH periodic table, which is a special type of periodic table designed by scientist Valery Tsimmerman. It can be easily found by doing a quick search online.
 In the ADOMAH periodic table, horizontal rows represent groups of elements (eg halogens, inert gases, alkali metals, alkaline earths, etc.). The vertical columns correspond to the electronic shells and the socalled "cascades" (diagonal lines that join the blocks s, p, d and f) correspond to the periods.
 Helium is placed next to hydrogen, since both are characterized by the 1s orbital. The period blocks (s, p, d and f) are shown on the right hand side and the layer numbers are shown at the bottom. The elements are presented in rectangular boxes numbered from 1 to 120. These are regular atomic numbers that represent the total number of electrons in a neutral atom.
Step 2. Find the atom in the ADOMAH table
If you want to write the electron configuration of an element, locate the symbol on the periodic table ADOMAH and cross out all the elements that have higher atomic numbers. For example, if you have to write the electron configuration of erbium (68), cross out elements 69 through 120.
Look at the numbers 1 through 8 at the bottom of the table. These are the numbers of the electron shells or columns. Ignore those that contain only crossedout items. In the case of erbium, the remaining columns are 1, 2, 3, 4, 5, and 6
Step 3. Count the orbital sets up to the atom you are working with
Look at the block symbols shown on the right side of the table (s, p, d, and f) and the column numbers shown at the bottom, and ignore the diagonal lines between the blocks. Then divide the columns into blocks and list them in order from bottom to top. Again, ignore column blocks in which all elements are crossed out. List the column blocks starting with the column number followed by the block symbol, like this: 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 6s (in the case of erbium).
 Note: the above electron configuration for Er is written in ascending order of the layer numbers. It could also be written in the order of filling of the orbitals. Just follow the cascades from the bottom up instead of the columns when scoring the blocks: 1s^{2} 2s^{2} 2 P^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{2} 4d^{10} 5 p^{6} 6s^{2} 4f^{12}.
Step 4. Count the electrons for each set of orbitals
Count the elements that you have not crossed out in each column block, assigning one electron per element and noting the amount next to the block symbols for each column, like this: 1s^{2} 2s^{2} 2 P^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{10} 4f^{12} 5s^{2} 5 p^{6} 6s^{2}. In the example, this is the electron configuration of erbium.
Step 5. Know the irregular electron configurations
There are 18 common exceptions to electron configurations for atoms in their lowest energy state, also known as the ground state. They deviate from the general rule only in the last 2 or 3 positions of the electrons. In these cases, the electron configuration itself keeps the electrons in a lower energy state than in a standard configuration for the atom. The irregular atoms are as follows:
 Cr (…, 3d5, 4s1); Cu (…, 3d10, 4s1); Nb (…, 4d4, 5s1); Mo (…, 4d5, 5s1); Ru (…, 4d7, 5s1); Rh (…, 4d8, 5s1); P. S (…, 4d10, 5s0); Ag (…, 4d10, 5s1); The (…, 5d1, 6s2); EC (…, 4f1, 5d1, 6s2); Gd (…, 4f7, 5d1, 6s2); Au (…, 5d10, 6s1); Ac (…, 6d1, 7s2); Th (…, 6d2, 7s2); Pa (…, 5f2, 6d1, 7s2); OR (…, 5f3, 6d1, 7s2); Np (…, 5f4, 6d1, 7s2) and Cm (…, 5f7, 6d1, 7s2).
Method 4 of 4: Special Cases and Exceptions
Step 1. Write the notation for cations
Dealing with cations is very similar to neutral atoms in their ground state. To start, remove the electrons from the p orbital at the outer end, then from the s orbital, and then from the d orbital.

For example, the electron configuration of calcium in its ground state (Z = 20) is 1s22s22p63s23p64s2 { displaystyle 1s ^ {2} 2s ^ {2} 2p ^ {6} 3s ^ {2} 3p ^ {6} 4s ^ { 2}}
. Sin embargo, el ion de calcio tiene dos electrones menos, por lo que empiezas quitándolos de la capa en el extremo exterior (que es la 4). Entonces, la configuración del ion de calcio es 1s22s22p63s23p6{displaystyle 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}}
Step 2. Write the notation for the anions
When writing the notation for an anion, you should use the Aufbau principle, according to which electrons fill the lowest available energy levels first before moving to higher levels. So you would add electrons to the energy level at the outer (or lower) end before moving inward to add more.

For example, neutral chlorine (Z = 17) has 17 electrons and is written 1s22s22p63s23p5 { displaystyle 1s ^ {2} 2s ^ {2} 2p ^ {6} 3s ^ {2} 3p ^ {5}}
. Sin embargo, el ion cloruro tiene 18 electrones, los cuales añadirías empezando por el nivel de energía en el extremo exterior. Por ende, el ion cloruro se escribe 1s22s22p63s23p6{displaystyle 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}}
Step 3. Chromium and copper
As with any rule, there are exceptions. Most of the elements follow the Aufbau principle, but these two elements are not. These electrons do not go to the lowest energy level but are added to the level that will make them more stable. It may be helpful to memorize the notation for these two items, as it doesn't follow the rule.

Cr = [Ar] 4s23d5 { displaystyle 4s ^ {2} 3d ^ {5}}
 cu = [ar] 4s13d10{displaystyle 4s^{1}3d^{10}}
consejos
 también es posible escribir la configuración electrónica de un elemento escribiendo solo la configuración de valencia, que es el último conjunto de orbitales s y p. entonces, la configuración de valencia de un átomo de antimonio sería 5s^{2} 5p^{3}.
 asimismo, puedes usar muchas calculadoras de configuración electrónica en línea de manera gratuita escribiendo el nombre del elemento. sin embargo, no suelen mostrar el cálculo.