Big Ideas Structure & Properties of Matter The nature of the attractive forces that exist between particles in a substance determines the properties, and limits the uses of that substance Technological devices that are based on the principles of atomic and molecular structures can have societal benefits and costs

Atomic Theory the theory that all matter is made up of tiny indivisible atoms atoms of each element are effectively identical, but differ from those of other elements, and unite to form compounds in fixed proportions http://www.youtube.com/watch?v=yQP4UJhNn0I

The Atomic Model What does an atom look like? The answer to this question has evolved over many years…

Democritus 460 BCE – 370 BCE Ancient Greek philosopher who proposed that if an object was cut-in-half over and over again, eventually you reach a point at which it could not be cut-in-half anymore This piece was said to be indivisible or (ἄτομος; “atomos”)

John Dalton 1803 Matter divided into small, indivisible atoms Each elements made of different atoms

Dalton’s Billiard Ball Model

JJ Thomson 1897 discovered positive/negative charges within atom   Cathode Ray Tube Experiment: http://www.youtube.com/watch?v=2xKZRpAsWL8

JJ Thomson’s Raisin Bun Model

Ernest Rutherford 1911 -discovered negative electron cloud surrounding central, positively charged nucleus Gold Foil Experiment http://www.youtube.com/watch?v=wzALbzTdnc8

Rutherford’s Beehive Model

Niels Bohr 1913 -described surrounding electrons to be locked into “orbits” of specific energy levels 

Bohr’s Solar System Model

Quantum Mechanics 17 of the 29 attendees were, or became, Nobel Prize Winners

Quantum Mechanical Model It turns out, that all those models were incomplete This is where the electrons really are… --------------------------

Quanta – plural Quantum – singular Atoms & electrons, cannot be seen, only modelled They are modelled by the way that they respond to energy (electormagnetic) input Energy is given to the particles (atoms/electrons etc) and the response is detected Hypotheses are formulated which are then tested by all available means If the experimental evidence seems to fit the hypothesis then a theory is proposed which in time comes to be accepted as the "truth“ or the “accepted model”

The Photon 1873: James Maxwell proposes that light is an electromagnetic wave that can exert forces on charged particles. Earlier scientists including Isaac Newton felt that light should be studied as particles 1887: Heinrich Hertz discovers the photoelectric effect

Bohr & Hydrogen Bohr excited electrons with light (photons) http://www.ibchem.com/IB/ibfiles/atomic/ato_swf/line_spec.swf