Periodic Table - Basics and Brief History

The discovery of the elements has been an ongoing process since ancient times, and our catalog of elements: The Periodic Table, has been growing slowly in our lifetime.

Brief Timeline

• Before the 1800s
  • All discoveries made in ancient times.
  • We had 36 elements at this point.
• 1800-1849
  • An impulse in discovery from the Scientific Revolution, Atomic Theory, and Industrial Revolution.
  • Gave us +22 elements.
• 1850-1899
  • An impulse cased by the Age of Classifying Elements and Spectrum Analysis.
  • Gave us +23 elements.
• 1900-1949
  • An impulse caused by the Old Quantum Theory, refinements of the Periodic Table, and Quantum Mechanics.
  • Gave us +13 elements.
• 1950-1999
  • An impulse caused by the Manhattan Project and Particle physics issues for the atomic number 97 and above.
  • Gave us +15 elements.

Periodic Law

The periodic law states that when our elements are arranged in order of increasing atomic number, striking similarities in their properties appear in regular periodic intervals.

Period

This is a horizontal section or row in the periodic table. Periods are indexed using Arabic numerals (Period 1, Period 2, etc.)

Group

This is a vertical section or column in the periodic table. Groups are divided into two groups: group A and B, and are indexed with either Roman numerals or Arabic numerals.

See also: Periodic Table - Periodic Trends

Periodic Table

A tabular arrangement of elements in increasing number of atomic number that illustrates the Periodic Law.

Contributing Figures

Johannes Dobereiner

Johannes Dobereiner was born in the year 1780 and died in the year 1849.

His contribution was the idea of classifying three elements that share similar properties into one group (referred to as Triads).

John Newland

John Newland was born in the year 1838 and died in the year 1898.

His contribution was his classification of elements into 11 groups that exhibited the Law of Octaves, which state that every 8th element repeated its physical and chemical properties. His proposal was later rejected due to it not holding true for elements heavier than Calcium ($Ca$).

Julius Lothar Meyer

Julius Lothar Meyer was born in the year 1830 and died in the year 1895. His contribution was being the first person to observe the trends among elements, specifically in regards to its atomic volume.

Formula for Atomic Volume : $V_m=\frac{M}{\rho }$

• $V_m$ ($m^3/mol$) = Molar Volume.
• $M$ ($g/mol$) = Molar Mass.
• $\rho$ ($mol/m^3$) = Molar Density.

Dimitri Mendeleev

Dimitri Mendeleev was born in the year 1834 and died on the year 1907.

He created the predecessor to the modern periodic table.

His periodic table was made by arranging the elements in the way that left blank spaces he claimed to be for unknown soon to be discovered elements.

He predicted the properties of these elements by observing the adjacent element’s properties and making an inference based on that.

He had 4 unknown elements which he had designated as Eka-Boron, Eka-Aluminum, Eka-Silicon, and Eka-Manganese with the atomic masses 44, 68, 72, 100.

• The prefix: eka, is Sanskrit for 1, which Mendeleev used this naming convention to denote that the element in question is 1 space away from the element in its name.
• These are 2 of those elements that were later discovered and given proper names.
  • Eka-Aluminum$\to$Gallium
  • Eka-Silicon$\to$Germanium

H.G.J. Moseley

H.G.J. Moseley was born in the year 1887 and died in the year 1915.

His contribution was the discovery of the underlying foundation of the elements; in his time, it was believed to be the elements atomic mass, but was later corrected by Moseley to be the atomic number.

Moseley is also the father of the modern periodic table.