Developments of Periodic Table Design

Developments of Periodic Table Design

• In 1829, Johann Döbereiner discovered similarities in properties among groups of three elements, which he called "triads".
• Döbereiner found that the atomic mass of the middle element in each triad was close to the average of atomic masses of the other two elements.

John Newlands and the Law of Octaves

• In 1865, John Newlands realized that the elements, when placed in order of increasing atomic weights, showed a cycle of properties repeating every eight elements, which he called the "law of octaves".

Dmitri Mendeleev and the Periodic Table

• In 1869, Dmitri Mendeleev published a periodic table that used the law of octaves as a predictive tool.
• Mendeleev's table organized elements in an eight-column format in order of increasing atomic mass, with each eighth element having similar properties.
• He left spaces for unknown elements and predicted their properties based on the chemistry of neighboring elements.

Predicting Unknown Elements

• Mendeleev's predictions included the properties of the missing element between silicon and tin, called eka-silicon (Es), which were later found to match the properties of germanium.

Limitations of Mendeleev's Table

• The table had three major problems: elements did not always fit in the group with matching properties, new elements were being discovered with no space in the table, and elements in the same group had different chemical reactivity.

Henry Moseley and the Modern Periodic Table

• Henry Moseley's work provided the crucial transition to the modern periodic table by placing elements in order of atomic number, removing irregularities, and defining exactly the spaces where elements still needed to be found.

Mendeleev's Periodic Law

• Mendeleev's periodic law states that the physical and chemical properties of elements are a periodic function of their atomic masses.
• He arranged elements in increasing order of atomic masses in horizontal rows (periods) and vertical columns (groups).