The Periodic TableHistory and Formulation

Definition of Terms

Periodic Table - is a tabular display of the chemical elements.

Periodic meaning:1. Having or marked by repeated cycles.2. Happening or appearing at regular intervals.3. Recurring or reappearing from time to time;

intermittent.4. Characterized by periodic sentences.

History• In 1789, Antoine Lavoisier published a list of

33 chemical elements.• Lavoisier grouped the elements into gases,

metals, non-metals, and earths. • Johann Wolfgang Döbereiner observed that

many of the elements could be grouped into triads (groups of three) based on their chemical properties. Lithium, sodium, and potassium, for example, were grouped together as being soft, reactive metals.

History

• Döbereiner also observed that, when arranged by atomic weight, the second member of each triad was roughly the average of the first and the third. Same is true for other properties like Density. These groups were known as Döbereiner’s triads.– chlorine, bromine, and iodine– calcium, strontium, and barium– sulfur, selenium, and tellurium– lithium, sodium, and potassium

• This became known as the Law of triads.

History

• John Alexander Reina Newlands published a series of papers in 1864 and 1865 that described his attempt at classifying the elements: When listed in order of increasing atomic weight, similar physical and chemical properties recurred at intervals of eight, which he likened to the octaves of music.

• This is what he called as the Law of Octaves.

History Dmitri Ivanovich Mendeleev and Julius

Lothar Meyer independently published their periodic tables in 1869 and 1870, respectively.

They both constructed their tables in a similar manner, by listing the elements in a row or column in order of atomic weight and starting a new row or column when the characteristics of the elements began to repeat.

History

• The success of Mendeleev's table came from two decisions he made:– The first was to leave gaps in the table when it

seemed that the corresponding element had not yet been discovered.

– The second decision was to occasionally ignore the order suggested by the atomic weights and switch adjacent elements, such as cobalt and nickel, to better classify them into chemical families.

History

• With the development of theories of atomic structure, it became apparent that Mendeleev had inadvertently listed the elements in order of increasing atomic number.

• The modern version of the periodic table was based on the Periodic Law, which states that when elements are arranged in an increasing atomic number, their physical and chemical properties show periodic pattern.

History