Electron-Configuration Diagrams


The Electron-Configuration Diagram

An electron-configuration diagram is a condensed representation of electrons in the shell of an atom where both the valence and kernel electrons are displayed. Since the valence electrons come into contact with other elements during chemical reaction, they are of primary interest. The quantity of kernel electrons present modifies how the valence electrons act, but both shape the chemical and physical properties of each element on the periodic table. The electron-configuration diagram represents the orbitals occupied, the number of electrons present and how the electrons are distributed in the orbitals. The number of electrons in the kernel is represented using the symbol of a noble element having the same number of total electrons. The number of electrons in sodium's kernel is ten, therefore the nobel element neon is used to represent sodium's kernel. Neon has a total of ten electrons. Only the noble elements He, Ne, Ar, Kr, Xe or Rn can presently be used as short-hand elements in electron-configuration diagrams. 



The Electron-Configuration Diagram Example One: Carbon

The first step in the process is to determine the number of electrons in the orbital-filling diagram of carbon. Carbon's atomic number is six, which identifies the electron count in its orbital-filling diagram. The second step is to determine carbon's short-hand element. Helium is carbon's short-hand element and it is the preceding nobel element. A second method for finding the shorthand element is counting backward on the periodic table starting from carbon. Carbon's number of valence electrons can be found by subtracting helium's electron count(2) from carbon's electron count(6): 6-2=4. Carbon has four valence electrons. See the the orbital-filling diagram in figure 1. In this case, the valence shell is written as 2s²2p². All the sublevels filled after the s and before the p in the valence shell would be included in the electron-configuration diagram. In the case of carbon, there are no orbitals filled after the s and before the p. The last two remaining electrons are in the kernel. The noble element that has just two electrons is helium. The electron-configuration diagram in figure 1 for carbon is [He]2s²2p².

The Electron-Configuration Diagram Example Two: Aluminum 

The first step in the process is to detemine the number of electrons in the orbital-filling diagram of aluminum. Aluminum's atomic number 13 identifies the electron count in its orbital-filling diagram. The second step is to determine aluminum's short-hand element. Neon is aluminum's short-hand element and it is the preceding nobel element. A second method for finding the shorthand element is counting backward on the periodic table starting from aluminum. Aluminum's number of valence electrons can be found by subtracting neon's electron count(10) from aluminum’s electron count(13): 13-10=3. Aluminum has three valence electrons. See the the orbital-filling diagram in figure 2. In this case the valence shell is written as 3s²3p¹. All the sublevels filled after the s and before the p in the valence shell would be included in the electron-configuration diagram. In the case of aluminum there are no orbitals filled after the s and before the p. The last ten remaining electrons are in the kernel. The noble element that has just ten electrons is neon. The electron-configuration diagram in figure 2 for aluminum is [Ne]3s²3p¹.

The Electron-Configuration Diagram Example Three: Bromine 

Bromine's atomic number 35 identifies it as having 35 electrons in its shell. Argon is determined to be bromine's short-hand element based on counting backwards on the periodic table starting from bromine. Bromine's number of valence electrons can be found by subtracting argon's electron count(18) from bromine's electron count(35): 35-18=17. Bromine has 17 valence electrons. See the the orbital-filling diagram in figure 3. In this case, the valence shell is written as 4s23d104p5. Any sublevels filled after the 4s and before the 4p in the valence shell, namely the 3d¹⁰, are included in the valence shell portion of the electron-configuration diagram. The 18 electrons not in the valence shell are in the kernel. The electron-configuration diagram in figure 3 for bromine is [Ar]4s23d104p5 .


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