GCSE Combined Science (AQA)

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Development of the Periodic Table

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Atomic structure and the periodic table The periodic table

Development of the Periodic Table

8:23 Periodic Table and Arrangement of Electrons
Spec 4.1.2.2
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  • The periodic table has evolved as scientific methods and theories have developed.
  • Initially, elements were arranged in order of atomic weights, not in a table format.
  • Early attempts to organize elements were simpler and not as structured as the modern periodic table.
  • Scientists initially arranged elements by atomic weight, now referred to as relative atomic mass.
  • John Newland in the 1860s suggested arranging elements in columns of seven, observing that every eighth element had similar properties.
  • Early periodic tables were incomplete due to unknown elements, leading to incorrect patterns and groupings.
  • Dmitri Mendeleev improved the periodic table by arranging elements with similar chemical properties in columns called groups.
  • Mendeleev left gaps for undiscovered elements, predicting their properties, which were later confirmed with discoveries like germanium.
  • Mendeleev swapped some elements out of atomic weight order to maintain consistent group properties.
  • The discovery of isotopes explained why atomic weight order was not always correct.
  • The modern periodic table is organized by increasing proton number, not atomic weight.
  • Mendeleev's predictions about element relationships were validated with later scientific discoveries.
  • Understanding the improvements Mendeleev made and subsequent developments is important for exams.

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