Examine more closely some of the elements in the table’s far right column in Figure 3. The periodic table is arranged in columns and rows based on the number of electrons and their location. Understanding that the periodic table’s organization is based on the total number of protons (and electrons) helps us know how electrons distribute themselves among the energy levels. How many electrons do elements in groups 14 and 17 need to gain to achieve a stable configuration? 4 and 1 electron respectively. Looking at this figure, how many electrons do elements in group 1 need to lose in order to achieve a stable electron configuration? 1 electron.
HYDROGEN ATOMIC NUMBER ELECTRON CONFIGURATION FULL
Elements in other groups have partially filled valence shells and gain or lose electrons to achieve a stable electron configuration.Īn atom may give, take or share electrons with another atom to achieve a full valence shell, the most stable electron configuration.
A full valence shell is the most stable electron configuration. Group 18 elements (helium, neon, and argon) have a full outer, or valence, shell. In contrast, chlorine and sodium have seven and one, respectively, in their outer shells, however, by following the octet rule they would be more energetically stable having eight.īohr diagrams indicate how many electrons fill each principal shell. Similarly, neon has a complete outer 2n shell containing eight electrons. Notice that h elium has a complete outer electron shell, with two electrons filling its first and only shell. Figure 2 sho ws examples of some neutral atoms and their electron configurations. This is known as the octet rule, which states, with the exception of the innermost shell, that atoms are more stable energetically when they have eight electrons in their valence shell, the outermost electron shell. The innermost shell has a maximum of two electrons but the next two electron shells can each have a maximum of eight electrons. Under standard conditions, atoms fill the inner shells first, often resulting in a variable number of electrons in the outermost shell. An electron normally exists in the lowest energy shell available, which is the one closest to the nucleus.Įlectrons fill shells in a consistent order: they first fill the shells closest to the nucleus, then they continue to fill shells of increasing energy further from the nucleus.The electrons of the outermost energy level determine the atom’s energetic stability and its tendency to form chemical bonds with other atoms to form molecules.
In the Bohr model, electrons exist within principal shells (n).
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