ATOMIC STRUCTUREProbing the Atom

Sir Ernest Rutherford

(1871-1937)

He is a New Zealand-born British chemist and physicist who became known as the father of nuclear physics. In early work he discovered the concept of radioactive half-life, proved that radioactivity involved the transmutation of one chemical element to another, and also differentiated and named alpha and beta radiation, proving that the former was essentially helium ions. This work was done at McGill University in Canada. It is the basis for the Nobel Prize in Chemistry he was awarded in 1908 "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances"

In 1911, Rutherford and his coworkers discovered that the alpha particles were helium atoms with their electrons removed. They were positive and very massive compared to the electron.

They focused a stream of high-speed alpha particles on a thin gold foil and observed how they would be scattered after passing through the foil.

Fig. 1: Rutherford's experiment

If Thomson’s model was correct, the alpha particles with their high-speed and heavy mass would all pass through the gold foil largely undeflected.

To their surprise, they observed that, in fact, most of the particles went straight through but there were a few that were scattered at wide angles and there were some, although fewer still, that were deflected by very large angles, and some occasional ones which practically bounced back to the source.

Based on these observations, they dismissed Thomson’s raisin bread model and proposed the ff:

The fact that most alpha particles were able to go through the foil implies that the gold atoms in the foil must be empty space.

An atom has a core that is very small.

The negatively charged electrons move around the nucleus and occupy most of the volume of the atom.

Fig. 1.2: The nuclear model of atom

Niels Bohr (1855-1962)

He was a Danish physicist who made foundational contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922.Bohr mentored and collaborated with many of the top physicists of the century at his institute in Copenhagen. He was part of a team of physicists working on the Manhattan Project. Bohr married Margrethe Nørlund in 1912, and one of their sons, Aage Bohr, grew up to be an important physicist who in 1975 also received the Nobel Prize. Bohr has been described as one of the most influential scientists of the 20th century.

In view of Rutherford’s model, he assumed that the prevailing laws of physics at that time were not sufficient to describe the atom. He proposed that the electrons move in orbits around the nucleus but only orbits of certain radii, corresponding to certain definite energies, are permitted. An electron in a permitted orbit has a specific energy and is said to be in an ‘allowed’ energy state. An electron in an allowed energy state will not radiate energy and therefore will not be spiral to the nucleus.

Fig. 2: Bohr’s Model

Lene Vestergaard Hau

(1959-present)

Was born in Denmark, on November 13, 1959) is a Danish physicist. In 1999, she led a Harvard University team who, by use of a superfluid, succeeded in slowing a beam of light to about 17 metres per second, and, in 2001, was able to momentarily stop a beam.In 1989, Hau accepted a two-year appointment as a postdoctoral fellow at Harvard University. She received her degree from the University of Aarhus in Denmark in 1991. Her formalized training is in theoretical physics but her interest moved to experimental research in an effort to create a new form of matter known as a Bose-Einstein condensate. In 1991 she joined the Rowland Institute for Science at Cambridge as a scientific staff member. Since 1999 she has held the Gordon McKay Professor of Applied Physics and Professor of Physics at Harvard. She now is the Mallinckrodt Professor of Physics and Applied Physics at Harvard.

Dr. Hau’s scientific and service contributions have been recognized through honors that include: the MacArthur Fellow 2001–2006; the NKT award, awarded by the Danish Physical Society, 2001; the Ole Rømer Medal, awarded by the president of the

University of Copenhagen, 2001; an Honorary Degree, Æreshåndværker Kjøbenhavns

Håndværkerforening, awarded in the presence of Her Majesty, Queen Margrethe II of Denmark, Copenhagen, 2001;

recipient of the Samuel Friedman Rescue Award, awarded by the Friedman Foundation, University of California, Los Angeles, 2001;

recipient of the Year 2000 Award from the Top Danmark Foundation, Copenhagen Denmark, 2000;

recipient of the J. C. Jacobsen 200 Year Anniversary Award, awarded by the Carlsberg Foundation, Denmark, 1989;

recipient of the Research Fellowship, 1986–1989, awarded by the Faculty of Sciences, University of Aarhus, Denmark.

Dr. Hau recently was awarded an honorary appointment to the Royal Danish Academy of Sciences and Letters and was elected a foreign member of the Royal Swedish Academy of Sciences in 2008.

She received in 2010 Danes Worldwide's annual awards "Årets Verdensdansker" [Best World Dane] because she, according to Danes Worldwide emphatically and persistently has put Denmark on the world map.

MEMBERS:

Cuisia, Marie Camille Agbunag, Nikka Aguirre, Patricia Chua, Selena Kyle Cordero, Cristina Marie Gambalan, Wendy Joaquin, Mary Joy Oliquino, Samantha