The law of octaves is Newlands' observation that, when the elements are arranged in order of increasing atomic mass, every eighth element has similar properties.
The law of octaves is Newlands’ observation that, when the elements are arranged in order of increasing atomic mass, every eighth element has similar properties. Malay: hukum oktaf · Chinese: 八音律.
This is part of the history of how the periodic table developed, which the syllabus expects you to know. John Newlands noticed that if the known elements were listed by increasing atomic mass, the properties seemed to repeat after every eighth element, like the notes of a musical scale, hence the musical name “octaves”. It was an important early hint that element properties are periodic, that is, they repeat at regular intervals, and this idea of periodicity is the seed of the modern table.
Example. In Newlands’ arrangement, counting eight along from one element often landed on another with similar behaviour, echoing how the eighth note of a scale sounds like the first. The pattern held reasonably for the lighter elements but broke down further along, because there was no room in a fixed group of eight for elements that had not yet been discovered.
Confusion to avoid. The law of octaves is a historical stepping stone, not the rule used today. Newlands ordered elements by atomic mass, whereas the modern periodic table is ordered by proton number, and the modern table also leaves room for whole families such as the transition elements that a rigid “every eighth” pattern could not accommodate.
In the Periodic Table of Elements chapter the law of octaves is one of the early contributions, alongside Döbereiner’s triads and Mendeleev’s table, that show how the idea of arranging elements by periodic properties grew into the table we use now.
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