Dobereiner's Law of Triads & Newlands' Law of Octaves

Dobereiner's Law of Triads & Newlands' Law of Octaves
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  • 0:04 Music & Chemistry
  • 0:40 Dobereiner's Law of Triads
  • 2:09 Newlands' Law of Octaves
  • 2:59 Breakdown of These Laws
  • 3:35 Lesson Summary
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Lesson Transcript
Instructor: Matthew Bergstresser
Dobereiner and Newlands were chemists in the 1800s and they devised the Law of Triads and Law of Octaves. In this lesson, we will investigate these laws in relation to the periodic table.

Music and Chemistry

In music, there are triads and octaves. A triad is a chord consisting of three notes, each three notes apart on the musical scale. An octave is the same note, but a different pitch, for example, low C, middle C, and high C. In the 1800s, two scientists came up the chemistry versions of triads and octaves, but they don't have anything to do with musical notes. What's similar to the musical version is the spaces between the elements involved in triads and octaves. Let's look at the chemistry versions of triads and octaves.

Dobereiner's Law of Triads

Johann Wolfgang Dobereiner was a chemist in the early 1800s, when the periodic table wasn't in existence, and some chemists were trying to find a type of organizational system for the known elements. Dobereiner noticed a pattern with certain elements that had similar chemical and physical properties. He called these elements triads and, thus, we have Dobereiner's Law of Triads. If you put these elements in order of their atomic masses, the average of the molar mass of the first and third elements in the triad is the molar mass of the second element. Let's look at an example.

The halogens, chlorine, bromine, and iodine, have atomic masses ≈ 35 g/mole, ≈ 80 g/mole, and ≈ 127 g/mole respectively. These values are rounded to the nearest g/mole. If we take the average of the masses of chlorine and iodine we get:

1/2(35 g/mole + 127 g/mole) = 81 g/mole, which is very close to bromine's atomic mass of 80 g/mole.

There are a few other triads:

  • Lithium, sodium, and potassium
  • Calcium, strontium, and barium
  • Phosphorus, arsenic, and antimony
  • Sulfur, selenium, and tellurium

If you locate these triads on the modern periodic table you'll see they are stacked vertically. Diagram 1 has the triads outlined.

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