An arrangement by atomic mass that predicted undiscovered elements by leaving gaps.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
Dmitri Mendeleev arranged the known elements in 1869 in order of atomic mass, but he grouped them by similar chemical properties. Where the properties did not fit, he left gaps and in some cases placed elements out of mass order, such as tellurium and iodine. He predicted the properties of undiscovered elements, which he called eka-aluminium, eka-boron and eka-silicon. These predictions were later confirmed by the discovery of gallium, scandium and germanium. His table laid the groundwork for the modern periodic table.
Key ideas: Mendeleev (1869) arranged elements by increasing atomic mass in rows and columns of similar properties, leaving gaps for undiscovered elements. He predicted eka-aluminium (gallium, found 1875), eka-silicon (germanium, 1886) and eka-boron (scandium), including density and oxide formulas. He swapped Te and I to keep chemical sense.
Common mistakes and connections: Students think his table had no flaws; it placed isotopes and noble gases poorly (they were unknown) and had pairs out of mass order (Ar and K, Co and Ni). The reason it worked is that atomic number correlates with mass. It was replaced by the modern atomic-number-based table.
Mendeleev predicted eka-silicon with mass 72 and density 5.5; germanium, found in 1886, has 72.63 and 5.32, confirming his table. The interactive lesson shows this as a live animation or chart.
Mendeleev predicted eka-silicon, now germanium, with a density near 5.5 g/cm3, close to the measured value of 5.35 g/cm3.
An arrangement by atomic mass that predicted undiscovered elements by leaving gaps.
Mendeleev's Periodic Table is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Atomic Structure & Periodicity first: Slater's Rules, Penetration of Orbitals, Periodic Law.
The next topics in Atomic Structure & Periodicity are Modern Periodic Table and Periods and Groups.
Yes. The interactive lesson includes a self-check question on Mendeleev's Periodic Table, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Mendeleev's Periodic Table is topic 75 of 115 in Atomic Structure & Periodicity.