A Chart Based on Atomic Numbers Showing the Electronic Structure of the Elements EDGAR I . EMERSON Trinity College, Hartford, Connecticut ITH but sl~ghtmodifications the long form of the . . ' penodlc table can be made to show the electronic configuration of the atoms in so far as the number of electrons in each shell is concerned. The table presented here is modified from many of the long forms as follows: (a) The noble gases are placed on the left and right sides of the table because they may be considered as starting and ending a series. (b) Element 0 has been included. ( 6 ) The relationship of hydrogen to the alkali metals and the halogens is shown by extending horizontally the space occupied by hydrogen. In a similar way the relation of be~ylliumand magnesium to the alkali earth metals and the zinc group is shown. This arrangement implies no break between hydrogen and helium or between magnesium and aluminum. (d) The heavy horizontal lines indicate that the elements in the spaces above are not to be considered as prototypes of the elements lying below. (e) The rare earths are between the vertical triple lines, and the transition metals between the double lines. The outermost shell of any series is called the A shell, the next to outermost the B shell, and the next the C
shell. When a newly added electron enters the A shell the element is said to belong to an A subgroup or family. Following this terminology the transition metals become members of the B families and the rare earths become members of a C family, since the newly added electrons enter the B and C shells, respectively. As pointed out in a previous paper' this terminology gives meaning to the family letters. Reference to the table shows: (a) The distribution of electrons in the various shells at the completion of any series. This is shown on the right side. (b) The shells which will receive electrons in a given series and the level of these shells with reference to the outside of the atom, as given by the letters A , B, and C. These are indicated a t the left of the table. (c) The number of electrons in the various shells receiving electrons. This is given by the numbers a t the bottom of the table. (d) The number of electrons in some of the elements (indicated by dots) which have dropped back from the A to the B shell. In order to find the electronic structure of an atom,
1
EMERSON. "A new spiral form of the periodic table," J.
CHEM.EDUC..21, 111 (1944).
FIGURE
2.-A
SHORT FORM OP THE PERIODIC TABLE ARRANGEDTO SHOW ATOMICSTRUCT.URE. IN THETABLE 1s INTERPRETED THE SAME WAYAS THAT IN FIGURE 1.
determine from the right side of the table the shells appearing in the series. Write down the letters of all of these shells and the number of electrons in them, omitting the numbers in italics. These are replaced by the numbers a t the bottom of the table under the particular element. The structure of helium is found either by reference to the structure indicated a t the right for the completed series or by the general scheme previously outlined using the letter inscription for helium a t the left of the table. If the process is carried out correctly the sum of the numbers of electrons equals the atomic number. When the periodic table is arranged in the way described we find that: 1. There is a place for the rare earths. 2. The table indicates the electronic structure of
the elements in so far as the number of electrons in each shell is concerned. 3. Hydrogen has a definite position in the table. 4. The table shows the continuous variation of properties from active metals to active nonmetals as electrons are added to the outer shell of the atoms. In the opinion of the author many long charts based on increasing atomic numbers either indicate directly 1, 3, and 4, or may be construed to do so by liberal interpretation. These same charts with but slight modification can also reflect the electronic structure of the element^,^ and i t should be mentioned that a scheme similar to the one described can be used to determine the electronic configuration of the atoms in the short form of the periodic table, Figure 2. ' For references to other tables rdeeting atomic structure see LIIDER, J. CHEM.EDIIC., 20, 21-6 (1943).
