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The first orbital, the s orbital, can hold two electrons at most. Every shell after the first can hold up to eight electrons. One can tell how many valence electrons an element has by taking its atomic number and seeing how many electrons are left over from the first 2 electrons plus 8 each shell thereafter. For example, Sodium has an atomic number 11, so it has 11 electrons. Since the first orbital is filled first, 2 electrons are taken, leaving nine electrons waiting to be placed. Eight of those nine can go in the next shell, leaving just one valence electron. Hope this is correct + makes sense!
Valence electrons are the electrons in the outer shell. If we use element carbon as an example. Carbon has the electron configuration [He]2s22p2. We can see that its outer shell is n=2, which is 2s and 2p. Thus, its valence electrons are 2+2=4.
Valence electrons are the number of electrons in the outer orbital. The number of electrons in orbitals go 2, and then 8 from there on. So, if you take P, with 15 electrons, you subtract 2, which gives you 13, then subtract 8, which gives you 5. That's how many valence electrons P has.
Hi! To determine how many valence electrons and element has, it is helpful to look at the period table, specifically the column number. For groups 1-2 and 13-18, there are specific numbers of valence electrons. Group 1 has one valence electron and group 2 has two valence electrons. Group 13 has 3 valence electrons, group 14 has 4 valence electrons, group 15 has 5 valence electrons, group 16 has 6 valence electrons, and group 17 has 7 valence electrons. Group 18 contains the noble gasses. These all have 8 valence electrons and are very stable.
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