What were the undiscovered elements of Mendeleev's periodic table?

He called the predicted element ekasilicon,we now know it as Ge.

Weren't there more then one?

eka-boron now Al

eka Si now Ge
eka Al now Ga
I understand there were two others but I've been unable to find them. I think one MAY have been Tc, element #43.

OK. I found it.

There were four that have been fairly widely spoken of; i.e.,
eka Al--Ga
eka B -- Sc
eka Si -- Ge
eka Mn -- Tc
After the discovery of He and Ar, Mendeleev placed those in his chart and predicted that there should be another group 0 element lighter than He and thought that it might be responible for radioactivity. Of course that never materialized since hydrogen is the lightest element known. In addition, he suggested an element heavier than He and Ar, which he named coronium (from the sun) since he observed a spectral line in the sun that had not been identified with any other element. That was later proved to be false, also. The calibration of the spectral instrument he used was not done correctly, the line was later remeasured and the new wavelength showed it to be iron, an element already known at the time. Good thing those later predictions weren't his first; otherwise, much of the popularity of his new table rested on the prediction of the new elements and their properties he would have been ridiculed instead of praised.

To determine the undiscovered elements of Mendeleev's periodic table, we need to understand the principles Mendeleev used to construct his periodic table. Mendeleev organized the known elements based on their atomic masses and chemical properties to identify patterns and similarities.

Mendeleev's periodic table had gaps or missing elements, which he predicted would be discovered in the future. He left empty spaces in his table where he believed new elements belonged, even though they had not yet been discovered or isolated.

The first significant prediction made by Mendeleev was the existence of elements with atomic masses in between those of known elements. For example, Mendeleev predicted the existence of an element with properties similar to aluminum but a higher atomic mass. This element was later discovered and named gallium.

Mendeleev's predictions also included elements that he believed would have properties similar to other elements in the same group or column. One prominent example is the element eka-silicon, which Mendeleev predicted would occupy the position below silicon in his periodic table. This element was eventually discovered and named germanium.

Other elements predicted by Mendeleev but were later discovered and named include scandium, technetium, and protactinium.

In summary, the undiscovered elements in Mendeleev's periodic table were those that he predicted would fill the gaps in the table based on patterns and similarities among the known elements. Many of Mendeleev's predictions turned out to be accurate, and the subsequent discovery of these elements confirmed the validity of his periodic table.