A great way to write the settings is to make a song out of it. Writing an electron configuration for an element is an excellent alternative to looking at the distribution of electrons in an atom. Depending on the item, this can be very extensive. Therefore, scientists have developed an abbreviated notation that consists of using a noble gas to represent electrons that are not valence electrons. This will simplify the electron configuration and make it easier to understand the chemistry of the element.
Part 1 of 2: Writing the Normal Electron Configuration of an Element
Step 1. Identify the number of electrons present in an element
The atomic number of an element tells you how many protons it contains. Since elements in their neutral state have the same number of protons and electrons, you can also use the atomic number as the number of electrons that element has. The atomic number, which can be found on the periodic table, is the number written directly above the element symbol.
For example, the symbol for sodium is Na. The atomic number of Na is 11
Step 2. Learn about electron shells and energy levels
The first electron shell only has the energy level s. The second layer has an energy level s and one p. The third layer has an energy level s, p, and d. the fourth layer has an energy level s, p, d and f. There are more than four shells of electrons, but in a standard chemistry course, you will normally use only the first four.
- Each energy level s can hold a maximum of 2 electrons.
- Each energy level p can contain a maximum of 6 electrons.
- Each energy level d can contain a maximum of 10 electrons.
- Each energy level f can contain a maximum of 14 electrons.
Step 3. Learn about the rules for electron filling
According to the Aufbau principle, you must add electrons to the lower energy levels before you can add an electron to a higher energy level. Each energy level can have multiple suborbitals, but each can hold a maximum of two electrons at any given time. The energy level s has one suborbital, p has 3 suborbitals, d has 5 suborbitals, and f has 7.
- The energy level d has a slightly higher energy than the level s of the lower electron shell, so the energy level s will fill up before the lower energy level d. In an electron configuration, it will look like this: 1s22s22 P63s23p64s23d10.
Step 4. Use the diagonal configuration table to write electron configurations
The easiest way to remember how to fill electrons is to use the configuration table. This is where you write each layer and the energy levels within it. Draw diagonal lines from the top right to the bottom left of each line. The configuration table will look like this:
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
- For example: The electron configuration of sodium (11 electrons) is 1s22s22 P63s1.
Step 5. Recognize what the last orbital of each configuration will be
By looking at the periodic table, you can determine what the last subshell will be and the energy level of the electron configuration. First determine in which block each element will be located (s, p, d, or f). Next, count which row the item is in. Finally, count in which column it is.
- For example, sodium is in the s block, so the last orbital of its electron configuration will be s. Also, it is located in the third row and in the first column, so that the last orbital is 3s1. This is a good way to check your final answer.
- The rule is slightly different for the d orbital. The first row of elements in block d starts in the fourth row, but you must subtract 1 from the row number because the s levels have less energy than the d levels. For example, vanadium ends with 3d3.
- Another way to check your answer is to add all the superscripts. They must be equal to the number of electrons in the element. If you have too few or too many electrons, you will need to check your work and try again.
Part 2 of 2: Writing the Noble Gas Electron Configuration
Step 1. Understand the electron configuration of noble gases
The noble gas electron configuration is a type of shortcut for writing the complete electron configuration of an element. The noble gas abbreviation is used to summarize the electronic configuration of an element while providing the most relevant information about the valence electrons of that element.
- The noble gas is replaced to represent all electrons that are not valence electrons.
- The noble gases are helium, neon, argon, krypton, xenon, and radon, and they are located in the last column of the periodic table.
Step 2. Identify the noble gas in the period before the element
The period of an element is the horizontal row in which that element is located. If the element is in the fourth row of the periodic table, it means that it is in period four. The noble gas that you will use will be found in period three. Here is a list of the noble gases and their periods:
- 1: helium
- 2: neon
- 3: argon
- 4: krypton
- 5: xenon
- 6: radon
- For example, sodium is in period three. We will use neon for the noble gas configuration because it is in period 2.
Step 3. Replace the noble gas with the same number of electrons as it has
There are a few ways to do this next step. You can physically write the electron configuration for the noble gas and then replace that same configuration in the element of your interest. An alternative is to remove the same number of electrons as the noble gas of the element for which you want to write the configuration.
- For example, sodium has 11 electrons, while neon has 10.
- The complete electron configuration for sodium is 1s2s222 P63s1 while the neon one is 1s2s222 P6. As you can see, sodium has a 3s1 that neon does not. Therefore, the noble gas configuration for sodium would be [Ne] 3s1.
- You can also count the superscripts of the energy levels up to ten. Eliminate these energy levels and leave the rest. By using neon to write the electron configuration of sodium, you will have one remaining electron: [Ne] 3s1.