This definitions covers Key Definitions within Development of Periodic Table for GCSE Chemistry. Revise Development of Periodic Table in Atomic Structure for GCSE Chemistry with 20 exam-style questions and 21 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 8 of 13 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
📖 Key Definitions
Relative atomic mass (Ar): The weighted mean mass of an atom of an element compared to one-twelfth of the mass of a carbon-12 atom. Takes account of the proportions of each isotope present.
Periodic law: The principle that the properties of the elements are a periodic (repeating) function of their atomic number.
Döbereiner's triads: Early grouping of elements into sets of three with similar properties, where the middle element's atomic weight approximated the mean of the other two (1817).
Newlands' octaves: Arrangement of elements by increasing atomic weight in which every eighth element showed similar properties, analogous to musical octaves (1866).
Atomic number: The number of protons in the nucleus — the property used to order elements in the modern periodic table (Moseley, 1913).
Practice questions for Development of Periodic Table
John Newlands proposed the Law of Octaves in 1866. What did he notice about the elements?
Give two reasons why Newlands' Law of Octaves was not accepted by the scientific community at the time.