8 Questions
What did Doberelmer's triads suggest about the arrangement of elements?
Doberelmer's triads suggested that elements could be grouped in sets of three, where the middle element's atomic mass is approximately the average of the other two.
What was a significant limitation of Doberelmer’s triads?
Not all known elements could be classified into triads based on their atomic masses.
What was the main principle behind Newlands' Law of Octaves?
The properties of elements repeat every eighth element when arranged by increasing atomic mass.
According to Doberelmer’s triads, how is the chemical property of the middle element of a triad related to the other two elements?
The chemical property of the middle element is similar to the properties of the elements at both ends of the triad.
Give an example of a triad from Doberelmer’s classification.
An example is the triad Li (6.94), Na (23.0), and K (39.1).
How did Newlands arrange elements to identify the recurring properties in his Law of Octaves?
Newlands arranged elements in order of increasing atomic mass.
Can you name the elements in the first triad of Doberelmer’s classification?
The elements are Lithium (Li), Sodium (Na), Potassium (K).
Explain why Doberelmer’s triads were eventually discarded.
They were discarded because they could not classify all known elements.
Study Notes
Periodic Classification of Elements
- The scientific word 'atom' was discovered by the ancient Greek.
- The classification of elements was essential to understand their properties.
Döbereiner's Triads
- In 1817, Döbereiner suggested arranging elements according to their atomic masses.
- Each group of similar and related elements constituted a triad.
- The chemical properties of the element in the middle of the triad were similar to the atomic masses of the elements at both ends.
- Examples of Döbereiner's triads include:
- Li, Na, K (average atomic mass of Li and K = 23.0, atomic mass of Na = 23.0)
- Cl, Br, I (average atomic mass of Cl and I = 81.2, atomic mass of Br = 80.0)
- Ca, Sr, Ba (average atomic mass of Ca and Ba = 88.7, atomic mass of Sr = 87.6)
- S, Se, Te (average atomic mass of S and Te = 80.0, atomic mass of Se = 78.96)
Newlands' Law of Octaves
- John Newlands suggested that the properties of elements vary periodically with their atomic masses.
- He observed that every eighth element has properties similar to the first, analogous to the recurrence of musical notes (octave).
- Newlands discovered a 'law of octaves' and noted properties of elements in ascending order of their atomic masses.
- The law of octaves was based on the arrangement of elements in order of increasing atomic mass.
Quiz on periodic classification of elements, covering Döbereiner’s Triads, Newland’s Law of Octaves, Mendeleev’s Periodic Table, and the Modern Periodic Table.
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