VOL.6 , NO.3
THE CHEMISTRY STUDENT
553
A PERIODIC CHART OF THE ATOMS* The chart shown in the accompanying illustration was drawn because of a desire on the part of the writer for a quick source of reliable information concerning the various chemical elements. In general design it is very similar to that of a chart compiled by Henry D. Hubbard of the U. S. Bureau of Standards. It does not, however, contain any information on subjects which cannot be readily understood by the student in high-
A PERI~DIC CIIARTO Q THE ATOMS
school chemistry. Placed on the wall of the home laboratory or study room, it has proved to be of great value in studying or in experimental work, as its use eliminates all loss of time in turning the pages of a book, in search for a table of atomic weights, valences, specific gravities, or other information. It is drawn in colored inks on a 32- by 24-inch sheet of mounted paper. Each of the ninety-two units contains the atomic weight, valence, etc., of one separate element. These units are arranged horizontally according to the number of orbits of electrons outside of the nuclei of the atomic systems, and vertically according to the number of electrons in the outside orbits of these atomic systems. The Arabic row numbers on the left-hand
' Winner of five-dollar award in the student contest closing February 15, 1929.
side designate the number of orbits in the atoms of that row, and the Roman column-head figures show the number of outer or valence electrons in the atoms of that column. In the lower right- and left-hand comers of the column-head sections are figures denoting the positive and negative valences of the elements below. Over elements 21 to 28, 39 to 46, and 57 to 78 a dotted line has been drawn, showing that these elements depart from the general rule and do not have the number of electrons in their outer orbit which the column head designates. The rare earths (atomic numbers 57 to 71), being of less importance, have been placed a t the foot of the chart. The second cut shown is a duplicate of the unit on the chart which contains the properties of the calcium (Ca) atom. The figure 20 in the upper left-hand comer is the atomic number of the element calcium and the upper right-hand corner contains the symbol. If this symbol is in black, the element is a solid a t ordinary temperatures; if in blue, it is a liauid:. if in red. it is a eas: and if in brown, it is a so-called "rare earth." The small figure a t the lower right-hand corner of the symbol shows the number of atoms in one molecule of the element, if this is known. Thus, by multiplying the atomic weight of the element by this small figure, the molecular weight of the element is obtained. l $ x n c r - S ~ DUPLICATE z~ O P THE CALCIUM UNIT In the center of the unit is the I f this is in green, the element is a metal; if in brown, it is a nonname. A green asterisk before the name of a non-metal shows that the elemetal. ment has metallic properties, and therefore we find this green mark before the name "hydrogen." A brown asterisk denotes ametal with non-metallic properties. We find such a mark before the name "chromium." Below the name of the element, at the left, is the atomic weight, and a t the right of this is the valence. At the bottom we find the specificgravity. If this is printed in blue, the specific gravity is basedupon the assumption that water = 1, and if it is red, air = 1. At one side of the unit is a diagram that shows the number of electrons in each orbit of that atomic system. At the opposite side there is a melting- and boiling-point graph. On this graph one-sixteenth of an inch equals 163 degrees, absolute temperature. The space on the graph through which the element remains a solid is colored in black; where it is a liquid the graph is blue; and where it is a gas it is red. The melting point in degrees Centigrade is printed in blue a t that point on the graph where the element melts, and the boiling point is printed in red at its point on the graph.
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By the arrangement of the units on this chart, elements of one family are seen to be in the same vertical column. Thus we find fluorine, chlorine, bromine, and iodine in the number VII column. The elements in one column which have their melting- and boiling-point graph on the same side of their unit more nearly resemble each other than those which do not. The chart is completed with a legend in the upper right-hand corner and an index to the elements in the lower right-hand corner.
