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 20 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. 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.
Topic position
Section 8 of 13
Practice
20 questions
Recall
20 flashcards
📖 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).