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Electron configuration of an atom is a series of numbers representing the electron orbitals. Electron Obitans are the spatial regions of different shapes surrounding an atom's nucleus, in which electrons are arranged in an orderly manner. Through electron configuration you can quickly determine how many electron orbitals are in the atom, and the number of electrons in each orbital. Once you understand the basic principles of electron configuration, you will be able to write your own electron configuration and be able to do chemistry tests with confidence.

Steps

Method 1 of 2: Determine the number of electrons using a chemical periodic table

1. 

   Find the atomic number of the atom. Each atom has a specific number of electrons associated with it. Locate the element on the periodic table. The atomic number is a positive integer starting at 1 (for hydrogen) and incrementing by 1 for each atom thereafter. The atomic number is the number of protons of the atom - so it is also the number of electrons of the atom in the ground state.
2. Determine the charge of the atom. An electrically neutral atom has the correct number of electrons as shown on the periodic table. However, an atom with a charge will have more or less electrons based on its charge magnitude. If you are working with atoms with a charge, add or subtract the corresponding number of electrons: add one electron for each negative charge and subtract one electron for each positive charge.
   • For example, a sodium atom with a charge of +1 will have one electron removed from the base atomic number 11. Therefore, the sodium atom will have a total of 10 electrons.
3. Memorize the basic orbital list. When an atom receives electrons, these electrons will be arranged into orbitals in a specific order. When the electrons fill orbitals, the number of electrons in each orbital is even. We have the following orbitals:
   • Obitan s (any number with an "s" behind in the electron configuration) has only one orbital, and follow The Principle Except for PauliEach orbital contains a maximum of 2 electrons, so each s orbital contains only 2 electrons.
   • Obitan p has 3 orbitals, so it can hold up to 6 electrons.
   • Obitan d has 5 orbitals, so it can hold up to 10 electrons.
   • Obitan f has 7 orbitals, so can hold up to 14 electrons. Memorize the order of the orbitals according to the following catchy sentence:
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     For atoms with more electrons, orbitals continue to be written alphabetically after the letter k, leaving out the characters that were used.
4. Understand electron configuration. Electron configurations are written so as to clearly show the number of electrons in the atom, as well as the number of electrons in each orbital. Each orbital is written in a certain order, with the number of electrons in each orbital written above the right of the orbital name. Finally the electron configuration is a sequence consisting of the names of the orbitals and the number of electrons written above to the right of them.
   • The following example is a simple electron configuration: 1s 2s 2p. This configuration shows that there are two electrons in the 1s orbital, two electrons in the 2s orbital, and six electrons in the 2p orbital. 2 + 2 + 6 = 10 electrons (total). This electron configuration is for an electrically neutral neon atom (neon's atomic number is 10).
5. Memorize the order of orbitals. Note that the orbitals are numbered according to the electron class, but are energetically ordered. For example, the 4s orbital is saturated with a lower energy (or more durable) than the saturated or unsaturated 3d orbital, so the 4s subclass is written first. Once you know the order of the orbitals, you can arrange the electrons into them according to the number of electrons in the atom. The order for placing electrons into orbitals is as follows: 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 with each electron-filled orbital is written like this: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d7p
   • Note that if all the layers are filled, the above electron configuration is that of Og (Oganesson), 118, which is the highest numbered atom on the periodic table - containing all currently known electron layers for with an electrically neutral atom.
6. Sort electrons into orbitals according to the number of electrons in the atom. For example, if you want to write the electron configuration of the electrically neutral calcium atom, the first thing to do is find its atomic number on the periodic table. The atomic number of calcium is 20, so we will write the configuration of an atom with 20 electrons in the order above.
   • Put your electrons in orbitals in the order above until you have reached 20 electrons. Obitan 1s gets two electrons, 2s gets two, 2p gets six, 3s gets two, 3p gets six, and 4s gets two (2 + 2 + 6 +2 +6 + 2 = 20). Hence the electron configuration of calcium is: 1s 2s 2p 3s 3p 4s.
   • Note: The energy level changes as the electron layer increases. For example, when you write to the 4th energy level, the 4s subclass is written first, later to 3d. After writing the fourth energy level, you will move on to the fifth level and re-start the layering order. This only happens after the 3rd energy level.
7. Use the periodic table as a visual shortcut. You may have noticed that the shape of the periodic table corresponds to the order of orbitals in electron configuration. For example, atoms in the second column from left to right always end at "s", atoms on the far right side of the middle section always end at "d", etc. Use the periodic table to write structures. figure - the order in which the electrons are placed into orbitals will correspond to the positions shown on the periodic table. See below:
   • The two leftmost columns are atoms whose electron configuration ends in the s orbital, the right part of the periodic table is atoms with an electron configuration ending in the p orbital, the middle part is atoms that end in the s orbital. d, and below are the atoms that end in the f orbital.
   • For example, when writing an electron configuration of the element chlorine, make the following argument: This atom is in the third row (or "period") of the periodic table. It is also in the fifth column of the p orbital block on the periodic table. So the electron configuration will end up ... 3p.
   • Careful! The d and f orbital classes on the periodic table correspond to energy levels different from their period. For example, the first row of the d orbital block corresponds to the 3d orbital even though it is in period 4, while the first row of the f orbital corresponds to the 4f orbital even though it is in period 6.
8. Learn how to write collapsible electron configurations. The atoms along the right edge of the periodic table are called rare gas. These elements are chemically very inert. To shorten the way to write long electron configurations, write in square brackets the chemical symbol for the nearest rare gas that has fewer electrons than that of the atom, and then continue to write the electron configurations of the next orbitals. . See below:
   • To understand this concept, write an example's collapsed electron configuration. Suppose we need to write the electron configuration for zinc reduction (atomic number 30) through a rare gas configuration. Zinc's full electron configuration is: 1s 2s 2p 3s 3p 4s 3d. Note, however, that 1s 2s 2p 3s 3p is the configuration for the rare agonic gas. Just replace this part of zinc's electron notation with the agonic chemical symbol in square brackets ().
   • Hence the electron configuration of zinc is compact 4s 3d.
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Method 2 of 2: Using the periodic table ADOMAH

1. 

   
   
   Explore the ADOMAH periodic table. This method of writing electron configuration does not require memorization. However, this method requires a rearranged periodic table, because in a regular periodic table, since the fourth row, the number of cycles does not correspond to the electron layer. Find an ADOMAH Periodic Table, a special chemical periodic table designed by scientist Valery Tsimmerman. You can find this periodic table on the internet.
   • On the ADOMAH Periodic Table, the horizontal rows are groups of elements such as halogens, inert gases, alkali metals, alkaline earth metals etc. The vertical columns correspond to the electron layer and are called "rungs" (diagonal junctions). blocks s, p, d and f) correspond to the period.
   • Helium is arranged next to hydrogen because both have a unique 1s orbital. The periodic blocks (s, p, d and f) are shown on the right side and the number of electron layers is shown at the base. Element names are written in a rectangle numbered 1 through 120. These numbers are the usual atomic numbers, representing the total number of electrons in an electrically neutral atom.
2. Find the element on the periodic table ADOMAH. To write an electron configuration for an element, locate its symbol on the ADOMAH Periodic Table and cross out all elements with higher atomic numbers. For example, if you want to write the electron configuration of eribi (68), cross out elements 69 through 120.
   • Note the numbers 1 through 8 at the base of the periodic table. This is the number of electron layers or columns. Do not pay attention to columns that have only crossed out elements.For eribi, the remaining columns are 1, 2, 3, 4, 5 and 6.
3. Count the number of orbitals to the position of the atom to write the configuration. Look at the block symbol shown to the right of the periodic table (s, p, d and f) and look at the number of columns shown at the base of the table, regardless of diagonal lines between blocks, divide columns into column-blocks and write they are in order from bottom to top. Skip column-blocks containing only crossed out elements. Write down the column-blocks starting with the column number and then the block symbol, like this: 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 6s (in the case of eribi).
   • Note: The above electron configuration for Er is written in ascending order of the number of electron layers. This configuration can also be written in the order of placing electrons into orbitals. Follow the steps from top to bottom instead of columns when writing column-blocks: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f.
4. Count the number of electrons per orbital. Count the number of electrons that are not crossed out in each column-block, assign one electron per element, and write the number of electrons next to the block symbol for each block-column, like this: 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 6s. In this example, this is the electron configuration of the eribi.
5. Recognize abnormal electron configurations. There are eighteen common exceptions to the electron configuration of atoms in the lowest energy state, also known as the ground state. Compared to the general rule of thumb, they only deviate from the last two to three electron positions. In this case, the actual electron configuration causes the electrons to have a lower energy state than the standard configuration of the atom. The unusual atoms are:
   • Cr (..., 3d5, 4s1); Cu (..., 3d10, 4s1); Nb (..., 4d4, 5s1); Mo (..., 4d5, 5s1); Ru (..., 4d7, 5s1); Rh (..., 4d8, 5s1); Pd (..., 4d10, 5s0); Ag (..., 4d10, 5s1); La (..., 5d1, 6s2); Ce (..., 4f1, 5d1, 6s2); Gd (..., 4f7, 5d1, 6s2); Au (..., 5d10, 6s1); Ac (..., 6d1, 7s2); Th (..., 6d2, 7s2); Pa (..., 5f2, 6d1, 7s2); U (..., 5f3, 6d1, 7s2); Np (..., 5f4, 6d1, 7s2) and Cm (..., 5f7, 6d1, 7s2).
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Advice

• When the atom is an ion, it means that the number of protons is not equal to the number of electrons. The charge of the atom is then shown in the (usually) upper right corner of the element's symbol. Therefore an antimony atom with charge +2 will have an electron configuration of 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p. Note that 5p is changed to 5p. Be careful when the configuration of an electrically neutral atom ends in any orbitals other than s and p. With electrons removed, you can only take electrons from the valence orbitals (s and p orbitals). So if a configuration ends at 4s 3d, and the atom has a charge of +2, the configuration changes to 4s 3d. We see 3dconstant, but only electrons in the s orbital are removed.
• All atoms tend to return to a stable state, and the most stable electron configuration will have enough s and p orbitals (s2 and p6). These rare gases have this electron configuration, which is why they rarely participate in reactions and are on the right side of the periodic table. So if a configuration ends at 3p, it only needs two more electrons to become stable (giving away six electrons, including the s orbital's electrons, would require more energy, so giving away four electrons would be easier. easier). If a configuration ends at 4d, it only needs to give away three electrons to reach a stable state. Likewise, the new subclasses that receive half of the electrons (s1, p3, d5 ..) are more stable, eg p4 or p2, but s2 and p6 will be even more stable.
• You can also use the valence electron configuration to write the electron configuration of an element, which is the last s and p orbitals. Therefore, the valence configuration of an antimony atom for an antimony is 5s 5p.
• Ions don't look like that because they are much more durable. Skip the above two steps of this article and work the same way, depending on where you start and how many or less electrons you have.
• To find the atomic number from its electron configuration, add all the numbers that follow the letters (s, p, d, and f). This is only correct if it is a neutral atom, if it is an ion you cannot use this method. Instead, you must add or subtract the number of electrons you take in or give away.
• The number follows the letter that must be written in the upper right corner, you must not write incorrectly when taking the test.
• There are two different ways to write electron configurations. You can write in the ascending order of the electron layer, or in the order in which the electrons are placed into orbitals, as shown for the eribi atom.
• There are instances where an electron needs to be "pushed up". That is when an orbital has only one electron missing to have half or all of the electrons, then you have to take an electron from the nearest s or p orbital to transfer it into the orbital that needs that electron.
• We cannot say that the "energy fraction stability" of the subclass receives half of the electrons. That is an over-simplification. The reason for the stability of the energy level of the new subclass receiving "half of the electrons" is that each orbital has only one single electron, so the electron-electron repulsion is minimized.