Its first two shells are full, and the remaining shells are empty. Helium, for instance, has a completely full inner shell, and all of its other shells are completely empty. These elements, called the noble gases, are happy just the way they are. Thus, elements toward the left side of the periodic table ( metals) tend to give away valence electrons, while elements toward the right side ( non-metals) tend to collect them. On the other hand, elements toward the right side of the periodic table, like oxygen and fluorine, find it easier to fill their shells (by adding an extra electron or two) rather than getting rid of their many valence electrons. Giving away two is much easier than collecting sixteen, of course, so calcium strongly prefers to give its two valence electrons away. Well, you don’t have to be a lithium atom to know that giving one electron away is much easier than begging your friends for seven of theirs! Similarly, the element calcium (the second element in the fourth row) could either give away its two valence electrons to empty its fourth shell, or collect sixteen more to fill that shell. To avoid the disgrace of having a partly-filled shell, lithium could either give away its valence electron (thereby emptying its second shell) or collect seven more (to fill that shell, which can hold eight). These elements are eager to give away that valence electron in a chemical reaction. It’s a noble gas, so it has no partly-filled shells and therefore no valence electrons.Ītoms of hydrogen and the alkali metals, which are listed in the first column of the periodic table, each have one valence electron. How many valence electrons does neon have? None. Since it’s the first element in its row, it has just one valence electron. How many valence electrons does sodium have? Sodium is the first element in the third row. (Notice that a number of columns are skipped when counting across the second row, because those columns don’t have any elements for this row.) Since it is the sixth element in its row, it has six valence electrons. How many valence electrons does an oxygen atom have? Oxygen is the sixth element in the second row.
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