Video Transcript
Mendeleev left gaps in his periodic table. Why did he do that? (A) Because there were elements that did not fit his pattern and so were excluded. (B) To separate metals and nonmetals. (C) To predict the existence of undiscovered elements. (D) So the table could have a square shape. (E) To make the table easier to read.
Dmitri Mendeleev, a Russian chemist, is often credited with creating the first periodic table. Mendeleev organized the known elements at the time by increasing atomic weight. He also grouped elements that had similar properties into the same column. Mendeleev noticed when ordering the elements that there appeared to be some elements missing. When there wasn’t an element with properties that he expected, he left a gap in his table. Mendeleev predicted the atomic weights and properties of these yet-undiscovered elements.
Three of the most notable elements Mendeleev predicted were expected to have atomic weights of 44, 68, and 72. He called these elements eka-boron, eka-aluminum, and eka-silicon. Each of these elements were later discovered and were found to have atomic weights and properties similar to those Mendeleev predicted.
So the reason why Mendeleev left gaps in his periodic table was to predict the existence of undiscovered elements, answer choice (C).
