Eli5: how does a periodic table work?
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The electron in an atom form shells around the nucleus, and the number in each shell is limited – 2 in the first, 8 in the second and third, and so on. You line up elements in rows by how many shells they have, then list them based on the number of electrons in the outer shell.
The amazing thing is, elements with the same number of electrons in the outer shell behave in similar ways. For he dample, the right column (noble gases) all have full outer shells, so they are highly unreactive. So each column has elements with similar properties.
The gaps in the upper rows is because the smaller shells have fewer options for how many electrons to have, and the familiar alignment with more elements to the right is because basing the position on how many spaces are left in the outer shell is best for grouping similar elements. Each row is called a “period”.
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