The electron configuration of an atom is a numerical representation of the orbits of the electrons. Electron orbits are the different regions around the atomic nucleus, where electrons are usually present. An electron configuration can tell the reader about the number of electro orbits an atom has, as well as the number of electrons occupying each orbit. Once you understand the basic principles behind electron configurations, you will be able to write your own configurations and handle your chemistry tests with confidence.
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Method 1 of 2: Determining Electrons Through the Periodic Table
Step 1. Find your atomic number
Each atom has a specific number of electrons. Find the chemical symbol for your atom in the periodic table above. The atomic number is a positive integer starting at 1 (for hydrogen) and increasing by 1 each time for subsequent atoms. This atomic number is also the number of protons in an atom - so it also represents the number of electrons in an atom with zero content.
Step 2. Determine the atomic content
Atoms with zero content will have the exact number of electrons listed in the periodic table above. However, the atom with the content will have a higher or lower number of electrons, depending on the size of the content. If you are dealing with atomic content, add or add electrons: add one electron for each negative charge and subtract one for each positive charge.
For example, a sodium atom with a content of -1 will have an extra electron in addition to its base atomic number, which is 11. So this sodium atom will have a total of 12 electrons
Step 3. Keep the list of standard orbits in your memory
When an atom gains electrons, it fills different orbits in a specific order. Each set of these orbits, when fully occupied, will contain an even number of electrons. The sets of these orbits are:
- The set of s orbitals (any number in the electron configuration followed by an "s") includes a single orbit, and, according to Pauli's Exclusion Principle, a single orbit can include a maximum of 2 electrons, so each set of s orbitals can contain 2 electrons.
- The p orbital set contains 3 orbits, and can include a total of 6 electrons.
- The d orbital set contains 5 orbits, so this set can include 10 electrons.
- The f orbital set contains 7 orbits, so it can include 14 electrons.
Step 4. Understand electron configuration notation
The electron configuration is written in a way that clearly displays the number of electrons in an atom and each orbit. Each orbit is written sequentially, with the number of electrons in each orbit written in lower letters and in a higher position (superscript) to the right of the orbit name. The final electron configuration is a collection of data on orbit names and superscripts.
For example, here's a simple electron configuration: 1s2 2s2 2p6. This configuration shows that there are two electrons in the 1s orbital set, two electrons in the 2s orbital set, and six electrons in the 2p orbital set. 2 + 2 + 6 = 10 electrons. This electron configuration applies to neon atoms that have no content (the atomic number of neon is 10.)
Step 5. Remember the order of the orbits
Note that although the set of orbits is numbered according to the number of electron layers, the orbits are ordered according to their energy. For example, a 4s2 containing a lower energy level (or potentially more volatile) than a 3d. atom10 which is partially or completely filled, so column 4s is written first. Once you know the order of the orbits, you can fill them in based on the number of electrons in each atom. The order of filling the orbits is as follows: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, 8s.
- An electron configuration for an atom with each completely filled orbit would look like this: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d107p68s2
- The list above, if all layers are filled in, will be the electron configuration for Uuo (Ununoctium), 118, which is the highest numbered atom on the periodic table - so this electron configuration contains all the electron layers currently known to exist in a neutral atom.
Step 6. Fill in the orbits based on the number of electrons in your atom
For example, if we wanted to write the electron configuration for a calcium atom without content, we would start by determining the atomic number of calcium on the periodic table. The number is 20, so we'll write the configuration for an atom with 20 electrons in the order above.
- Fill the orbits following the above sequence until you reach a total of 20 electrons. The 1s orbit contains two electrons, 2s orbit two, 2p orbit six, 3s orbit two, 3p orbit six, and 4s orbit two (2 + 2 + 6 +2 +6 + 2 = 20.) So, the electron configuration for calcium is: 1s2 2s2 2p6 3s2 3p6 4s2.
- Note: Energy levels change as your orbit gets bigger. For example, when you will reach 4th energy level, then 4s will be first, then 3d. After the fourth energy level, you will go to the 5th level where the sequence returns to the beginning. This only happens after the 3rd energy level.
Step 7. Use the periodic table as your visual shortcut
You may have noticed that the shape of the periodic table represents the order of the set of orbits in the electron configuration. For example, the atoms in the second column from the left always end in "s2", the atoms in the right-hand region of the thin center always end in "d10, " etc. Use the periodic table as your visual aid in writing down the configurations of electrons - the order of electrons you write in orbits is directly related to your position on the table. See below:
- Specifically, the two leftmost columns represent atoms with electron configurations ending in s orbitals, the right half of the table represents atoms with electron configurations ending in s orbits, the middle sections represent atoms ending in d orbits, and the bottom half for atoms ending in d orbitals. orbits f.
- For example, when you want to write the electron configuration for chlorine, think: "This atom is in the third row (or "period") of the periodic table. It is also in the fifth column of the p-orbit block of the periodic table. So, the configuration the electron will end up with …3p5
- Caution - the d and f orbital regions in the table represent different energy levels with the row in which they are located. For example, the first row of d orbital blocks represents 3d orbits even though they are located in period 4, while the first row of f orbits represents 4f orbits even though they are actually in period 6.
Step 8. Learn how to quickly write electron configurations
The atoms on the right side of the periodic table are called noble gases. These elements are very chemically stable. To shorten the lengthy process of writing electron configurations, write the chemical symbol of the nearest gaseous element that has fewer electrons than atoms in your brackets, then continue with the electron configuration for the set of orbits that follow. See the example below:
- To make it easier for you to understand this concept, an example configuration has been provided. Let's write the configuration for Zinc (with atomic number 30) using the noble gas fast method. The overall electron configuration of Zinc is: 1s2 2s2 2p6 3s2 3p6 4s2 3d10. However, note that 1s2 2s2 2p6 3s2 3p6 is the configuration for Argon, a noble gas. Replace this part of the Zinc electron notation with the chemical symbol Argon in brackets ([Ar].)
- So, the electron configuration of Zinc can be written quickly as [Ar]4s2 3d10.
Method 2 of 2: Using the ADOMAH Periodic Table
Step 1. Understand the ADOMAH Periodic Table
This method of writing electron configurations doesn't require you to memorize them. However, it is necessary to rearrange the periodic table, because in the traditional periodic table, starting from the fourth row, the period number does not represent the electron layer. Look for the ADOMAH Periodic Table, which is a periodic table specially designed by scientist Valery Tsimmerman. You can find it easily through an online search.
- In the ADOMAH Periodic Table, the horizontal rows represent element groups, such as halogens, weak gases, alkali metals, alkaline earths, etc. The vertical columns represent the electron layers and are called “cascades” (diagonal lines connecting the s, p, d and f blocks) which correspond to the period.
- Helium is moved next to Hydrogen, because both have 1s orbits. Several periods (s, p, d and f) are shown on the right and the layer numbers are below. The elements are shown in rectangular boxes numbered from 1 to 120. These numbers are normal atomic numbers representing the total number of electrons in a neutral atom.
Step 2. Find your atom in the ADOMAH table
To write the electron configuration of an element, locate the symbol on the ADOMAH Periodic Table and cross out all elements with the higher atomic number. For example, if you want to write down the electron configuration of Erbium (68), cross out elements 69 through 120.
Notice the numbers 1 through 8 at the bottom of the table. These numbers are the electron layer numbers, or column numbers. Ignore the columns that contain only the elements you've crossed out. For Erbium, the remaining columns are column numbers 1, 2, 3, 4, 5 and 6
Step 3. Calculate your atomic finite set of orbits
By looking at the block symbols on the right side of the table (s, p, d, and f) and the column numbers at the bottom of the table and ignoring the diagonal lines between the blocks, divide the columns into columns. -block and write them in order from bottom to top. Again, ignore the column blocks that include all the crossed out elements. Write down the block-column beginnings starting with the column number and then followed by the block symbol, like this: 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 6s (in case of Erbium).
Note: The electron configurations of Er above are written in increasing order of layer number. You can also write in the order in which the orbits are filled. Follow the cascade from top to bottom (not columns) as you write column-blocks: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f12.
Step 4. Count the electrons in each set of orbits
Count the unstripped elements in each column-block, entering one electron per element, then write the number after the block symbol for each column-block, like this: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f12 5s2 5p6 6s2. In our example, this is the electron configuration of Erbium.
Step 5. Know the erratic electron configuration
There are eighteen exceptions to the electron configuration for atoms with the lowest energy level, or what is commonly called the elementary level. This exception breaks the general rule in the positions of the last two to three electrons. In such a case, the actual electron configuration keeps the electron in a lower energy state than in the atom's standard configuration. These erratic 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); Air conditioning (…, 6d1, 7s2); Th (…, 6d2, 7s2); Pa (…, 5f2, 6d1, 7s2); U (…, 5f3, 6d1, 7s2); Np (…, 5f4, 6d1, 7s2) and cm (…, 5f7, 6d1, 7s2).
Tips
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When an atom is an ion, this means that the number of protons does not equal the number of electrons. The atomic content will (usually) be shown in the upper right corner of the chemical symbol. Thus, an antimony atom with a +2 content will have an electron configuration of 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p1. Note that 5p3 changed to 5p1. Be careful when the electron configuration ends in an orbit other than the set of s and p orbits.
When you remove an electron, you can only remove it from its valence orbit (s and p orbit). So if a configuration ends in 4s2 3d7, and the atom gets a +2 content, then the configuration will change to ending in 4s0 3d7. Note that 3d7no changes, however, the s electron orbit is lost.
- Every atom wants to be stable, and the most stable configurations will contain the full set of s and p orbits (s2 and p6). Gases begin to have this configuration, which is why they are rarely reactive and are located on the right side of the periodic table. So if a configuration ends with 3p4, so this configuration requires only two additional electrons to become stable (removing six, including electrons in the s orbital set, requires more energy, so removing four is easier to do). And if a configuration ends at 4d3, then this configuration only needs to lose three electrons to reach a stable state. Also, layers with half content (s1, p3, d5..) are more stable than (for example) p4 or p2; however, s2 and p6 will be even more stable.
- There is no such thing as a "half-content balance" sublevel. This is a simplification. All balances associated with "half-filled" sublevels are based on the fact that each orbit has only one electron, so that the repulsion between the electrons is minimized.
- You can also write down the electron configuration of an element by simply writing its valence configuration, i.e. the last set of s and p orbits. So, the valence configuration of an antimony atom will be 5s2 5p3.
- The same is not true for ions. Ions are more difficult to write. Skip two levels and follow the same pattern, depending on where you start writing, based on how high or low the number of electrons is.
- To find the atomic number when it is in its electron configuration form, add up all the numbers that follow the letters (s, p, d, and f). This principle only applies to neutral atoms, if this atom is an ion, you must add or remove electrons according to the number added or removed.
- There are two different ways to write electron configurations. You can write them in order of layer number upwards, or the order in which the orbits fill, as in the example above for the element Erbium.
- There are certain circumstances in which electrons need to be "promoted." When a set of orbits requires only one electron to make it full or half full, remove one electron from the nearest set of s or p orbits and move it to the set of orbits that require that electron.
- Numbers following letters are superscript, so don't write them down on your test.
