Today in Science History – February 4 – Hund’s Rule

Friedrich Hund
Friedrich Hund (1896 – 1997)

February 4 is Friedrich Hund’s birthday. Hund was a German physicist best known for Hund’s Rule.

Hund’s Rule is a method to determine the electron structure within atoms and molecular bonds at the valence energy level. Once the inner electron levels are full, the leftover electrons distribute themselves in the valence shell by the spin quantum number. The spin quantum number has two possible values, +½ and -½, also known as “spin up” and “spin down”. Hund’s rule states the electrons will fill all available positions with the same spin before the electrons pair up and opposite spin values are added.

Hund proposed other rules dealing with molecular electron energy levels and molecular orbital theory. He also discovered the principle of quantum tunnelling. Quantum tunnelling is the quantum effect where a particle passes through, or ‘tunnels’ through an energy barrier where under classical mechanics, the particle could not overcome.

Notable Science History Events for February 4

1974 – Satyendra Nath Bose died.

Satyendra Nath Bose
Satyendra Nath Bose (1894 – 1974)

Bose was an Indian mathematical physicist who laid much of the groundwork of quantum mechanics in the 1920s, particularly the Bose-Einstein statistics and the Bose-Einstein condensate.

The boson particle was given his name in his honor by Paul Dirac.

1936 – The first artificial synthesis of a radioactive substance.

John Jacob Livingood bombarded bismuth with deuterons to create the isotope 210Bi, creating the first artificial synthesis of a natural radioactive substance.

1928 – Hendrik Antoon Lorentz died.

Hendrik Antoon Lorentz
Hendrik Antoon Lorentz (1853 – 1928)

Lorentz was a Dutch physicist who derived the transformation equations used by Einstein to describe the effects of motion on space and time in his relativity theory. Lorentz determined that moving frames of reference would measure time and distances differently from a stationary frame of reference.

He also shared the 1902 Nobel Prize with Pieter Zeeman for describing what is known as the Zeeman effect. The Zeeman Effect describes the splitting of elemental spectral lines when the sample is exposed to a magnetic field.

1906 – Clyde William Tombaugh was born.

Clyde William Tombaugh
Clyde William Tombaugh (1906 – 1997).
Lowell Observatory Archives

Tombaugh was an American astronomer who discovered the dwarf planet, Pluto, while searching for Percival Lowell and William Pickering’s Planet X that would explain the orbit of Neptune. He also discovered 14 asteroids. Tombaugh claimed he observed lights near Las Cruces, New Mexico he claimed were UFOs.

1896 – Friedrich Hund was born.

1875 – Ludwig Prandtl was born.

Ludwig Prandtl
Ludwig Prandtl (1875 – 1953) DLR-Archiv Göttingen

Prandtl was a German physicist who developed the mathematics involved in the science of aerodynamics. He identified the boundary layer of a fluid where the behavior of the fluid is different between the area up close to a surface and further away from the surface. He later developed the first theories of supersonic shockwaves with his student Theodor Meyer and created the first supersonic wind tunnels.

1847 – Henri Dutrochet died.

Henri Dutrochet (1776 - 1847)
Henri Dutrochet (1776 – 1847)

Dutrochet was a French physiologist who was best known for his discovery of osmosis. He was also the first to recognize the green pigment in plants is important to how plants take up carbon dioxide.

1749 – Thomas Earnshaw was born.

Thomas Earnshaw
Thomas Earnshaw (1749 – 1829)

Earnshaw was an English watchmaker that was the first to develop a method to create chronometers inexpensive enough for the general public to afford. He also improved marine chronometers to be more accurate.