![]() ![]() Because its 2n shell is filled, it is energetically stable as a single atom and will rarely form chemical bonds with other atoms. For instance, lithium ( Li \text Ne start text, N, e, end text ), on the other hand, has a total of ten electrons: two are in its innermost 1 s 1s 1 s 1, s orbital and eight fill the second shell-two each in the 2 s 2s 2 s 2, s and three p p p p orbitals, 1 s 2 1s^ 2 1 s 2 1, s, squared 2 s 2 2s^ 2 2 s 2 2, s, squared 2 p 6 2p^6 2 p 6 2, p, start superscript, 6, end superscript. Elements in the second row of the periodic table place their electrons in the 2n shell as well as the 1n shell. After the 1 s 1s 1 s 1, s orbital is filled, the second electron shell begins to fill, with electrons going first into the 2 s 2s 2 s 2, s orbital and then into the three p p p p orbitals. The second electron shell, 2n, contains another spherical s s s s orbital plus three dumbbell-shaped p p p p orbitals, each of which can hold two electrons. Hydrogen and helium are the only two elements that have electrons exclusively in the 1 s 1s 1 s 1, s orbital in their neutral, non-charged, state. On the periodic table, hydrogen and helium are the only two elements in the first row, or period, which reflects that they only have electrons in their first shell. This is written out as 1 s 2 1s^ 2 1 s 2 1, s, squared, referring to the two electrons of helium in the 1 s 1s 1 s 1, s orbital. Helium has two electrons, so it can completely fill the 1 s 1s 1 s 1, s orbital with its two electrons. At the very bottom is the name of the element (e.g., hydrogen). Below is the relative atomic mass, as calculated for the isotopes found naturally on Earth. In the middle is the letter symbol for the element (e.g., H). At the upper left is the atomic number, or number of protons. (credit a: modification of work by Serge Lachinov credit b: modification of work by Den fjättrade ankan/Wikimedia Commons) Video 3.2.2: An introduction to the organization of the periodic table into periods and groups. Image showing the 'anatomy' of a periodic table entry. ![]() This can be written out in a shorthand form called an electron configuration as 1 s 1 1s^ 1 1 s 1 1, s, start superscript, 1, end superscript, where the superscripted 1 refers to the one electron in the 1 s 1s 1 s 1, s orbital. Figure 3.2.1: (a) Dimitri Mendeleev is widely credited with creating (b) the first periodic table of the elements. Hydrogen has just one electron, so it has a single spot in the 1 s 1s 1 s 1, s orbital occupied. As of 2023, the element with the highest atomic number known is oganesson (Z 118), which completes the seventh period (row) in the periodic table. The 1 s 1s 1 s 1, s orbital is the closest orbital to the nucleus, and it fills with electrons first, before any other orbital. An extended periodic table theorises about chemical elements beyond those currently known in the periodic table and proven. ![]() The first electron shell, 1n, corresponds to a single 1 s 1s 1 s 1, s orbital. ![]()
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