Writing the Normal Electron Configuration of an Element
- 1Identify the number of electrons present in the element. The atomic number of an element tells you the number of protons it has. Because 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 the element has. The atomic number, which can be found on the periodic table, is the number written directly above the symbol for the element.
2Know about electron shells and energy levels. The first electron shell has only the s energy level, the second electron shell has both an s and p energy level. The third electron shell has an s, p, and d energy level. The fourth electron shell has an s, p, d, and f energy level. There are more than four electron shells, but for a standard chemistry course you will generally only use the first four.
- For example, the symbol for sodium is Na. The atomic number for Na is 11.
3Learn the rules for electron filling. According to the Aufbau principle, you must add electrons to the lowest energy levels before an electron can be added to a higher energy level. Each energy level may have multiple suborbitals, but each suborbital can hold a maximum of two electrons at any given time. The s energy level has one suborbital, p has 3 suborbitals, d has 5 suborbitals, and f has 7 suborbitals.
- Each s energy level can hold a maximum of 2 electrons.
- Each p energy level can hold a maximum of 6 electrons.
- Each d energy level can hold a maximum of 10 electrons.
- Each f energy level can hold a maximum of 14 electrons.
4Use the diagonal configuration chart to write electron configurations. The easiest way to remember how electrons fill is to use the configuration chart. This is where you write out each shell and the energy levels within it. Draw diagonal lines from the top right through to the bottom left of each line. The configuration chart looks like this:
- The d energy level has a slightly higher energy than the s energy level of the lower electron shell, so the higher s energy level will fill before the lower d energy level. For writing an electron configuration this means it will look like this: 1s22s22p63s23p64s23d10.
5Recognize what the last orbital of each configuration will be. By looking at the periodic table, you can determine what the last subshell and energy level of the electron configuration will be. First determine which block the element falls in (s, p, d, or f). Then count which row the element is in. Finally, count which column the element is in.
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
- For example: The electron configuration of sodium (11 electrons) is 1s22s22p63s1.
- For example, sodium is in the s block, so the last orbital of its electron configuration will be s. It is in the third row and the first column, therefore the last orbital is 3s1. This is a good way to double-check your final answer.
- The rule is a little bit different for the d orbital. The first row of d-block elements starts in the fourth row, but you must subtract 1 from the row number because the s levels are lower energy than the d levels. For example, vanadium ends with 3d3.
- Another way to double check your work is to add all of the superscripts together. They should equal the number of electrons in the element. If you have too few or too many electrons, you will need to look over your work and try again.
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Source: wikihow. com