For example, magnesium (Mg) and calcium (Mg) are found in column two and share certain similarities while potassium (K) and calcium (Ca) from row four share different characteristics. Each row and column has specific characteristics. As with any grid, the periodic table has rows (left to right) and columns (up and down). Each element is placed in a specific location because of its atomic structure. To maximize the total spin, the electrons in the orbitals that contain only one electron all possess the same spin, i.e., the exact values of the spin quantum number.The periodic table is organized like a big grid. The Hund’s rule describes the order in which electrons are filled in all the orbitals belonging to a sub-shell. It states that electrons singly occupy every orbital in a given sub-shell before a second electron occupies its space. Thus, if the principal, azimuthal, and magnetic numbers are the same for two electrons, they must have opposite spins. In another way, we can say no two electrons in the same atom can have the same values for all four quantum numbers. Pauli-Exclusion PrincipleĪccording to this rule, a maximum of two electrons, each having opposite spins, can fit in an orbital. However, exceptions exist to the Aufbau principle, such as chromium and copper, explained by the stability provided by half-filled or completely filled sub-shells. In the case of an equal ‘n+l’ value, the orbitals having a lower ‘n’ value are filled first. Whereas the energy level of an orbital is calculated by the sum of the principal (n) quantum number and the azimuthal (l) quantum numbers, written as n+l. Aufbau PrincipleĪufbau means “building up” in German, so this rule states that electrons will occupy the lower energy orbitals before occupying those with higher energy. However, the electrons follow some general rules while entering an orbital. Rules for Filling Atomic Orbitals in OrderĪs discussed, the number of electrons in each atomic orbital of every sub-shell determines the electronic configuration of that particular atom. Thus, the electron configuration of chlorine can be given as 1s 22s 22p 63s 23p 5 or as 3s 23p 5. Its 17 electrons are distributed as follows: 2 (in K shell), 8 (in L shell), and 7 (in M shell). Therefore, the electron configuration of oxygen is 1s 22s 22p 4 or 2s☢p4.Ĭhlorine has the atomic number 17. It implies that an oxygen atom has 8 electrons, filled in the following order: 2 (in K shell) and 6 (in L shell). Electron Configuration of Some Other Common Elements So, the abbreviated notation for argon would be 3s☣p⁶. Similarly, the electronic configuration of argon is written using its nearest inert neighbor neon, having the electronic configuration 1s 22s 22p 6. The electron configuration of argon is 1s 22s 22p 63s 23p 6 and thus the abbreviated notation of potassium (K) is written as 4s 1. Let us consider the element potassium (k), written using its nearest noble gas configuration, i.e., argon. Here, the sequence of filled sub-shells corresponding to the electronic configuration of its closest noble gas is replaced with the symbol of that noble gas using square brackets. In those elements, an abbreviated or condensed notation is used. However, the standard notation often gives lengthy electron configurations, mainly for elements having a relatively large atomic number. ![]() Similarly, the configuration of phosphorous, located in the third period and within the p-block, is 1s 22s 22p 63s 23p 3. Here, 1s, 2s, 3s, 3p, and 4s represent the sub-shells, whereas their superscripts denote the number of electrons in each sub-shell. The electron configuration of potassium (K) is 1s 22s 22p 63s 23p 64s 1. Systems having a large number of electrons will occupy greater energy levels. Here, only one electron in the s orbital has the principle energy level of 1. The first integer, 1, represents the principle energy level, the letter ‘s’ represents the type of orbital (sublevel), and the superscript 1 gives the electron occupancy.
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