Evolution of the Atomic Theories and Models

Aristotle vs. Democritus

Democritus- Greek, lived approximately 2,500 years ago

all matter consisted of extremely small particles called atoms (from the word atomos)

these atoms are indivisible (the word atomos means uncut or indivisible)

• Aristotle- Greek , lived approximately 2,500 years ago as well
• No limit to the number of matter can be divided
• Structure of matter consists of one or a combination of the four elements

Erwin Schrödinger

1887-1961

Schrödinger's model of the atom is the most recent and the one we reference today. It is the electron cloud model. The area where an electron is most likely to be is shaded darker and less likely is lighter but there is no clear location of the electron.

James Chadwick

1891-1974

John Dalton

British, born in 1766

Chadwick confirmed the existence of neutrons. Working under Ernest Rutherford, Chadwick noticed that a helium atom had an atomic number of two (2 protons) but an atomic mass/mass number of four. It was hypothesized that there were extra protons and neutrons which balanced each other out, but according to the Uncertainty Principle, there couldn't be electrons in the nucleus. Chadwick deemed this extra mass in the nucleus neutrons, which have no charge at all.

Was a teacher and did science in his spare time

had an interest in predicting weather

interest in weather led him to study the behavior of gases

noticed that compounds have fixed compositions (elements combined in fixed ratios to make compounds)

came up with the atomic theory

Atomic Theory

• All matter is made up of individual particles called atoms, which cannot be divided.
• all elements are composed of atoms
• all atoms of the same element have the same mass (atoms of different elements have different masses)
• compounds contain atoms of more than one element
• in a particular compound, atoms of different elements always combine the same way (fixed ratio)
• model: solid not hollow like a solid ball

Werner Heisenberg

1901-1976

Heisenberg did not create a model of the atom but he did discover one very important idea in the evolution of the atomic model, the Uncertainty Principle. The Uncertainty Principle stated that it is not possible to know the exact location of an electron but one can make an appropriate guess as to where an electron is most likely to be found.

Fun Facts:

born in Germany

worked under Bohr

Won the Nobel Prize in Physics in 1932

After WWII, he was taken by American troops and sent to England

Louis de Broglie

1892-1987

Building off of Bohr's model de Broglie (pronounced: deh broh-glee) thought that instead of orbiting in a uniform way, the electrons orbited in wave-like patterns (see below model).

Fun Fact:

won the Nobel Prize in Physics for discovery of the wave pattern of electrons in 1929

Niels Bohr

1885-1962

Joseph John (J. J.) Thomson

1856-1940

For a while, Bohr worked under Rutherford and accepted his model of the atom. However, there was one thing he didn't understand: why the electrons wouldn't attract to the protons in the nucleus and collapse the atom. So he came up with a new model and a new theory.

Theory:

electrons exist on specific energy levels and orbit at a constant speed around the nucleus (like the planet orbiting around the sun)

electrons cannot be between energy levels

Thomson used a cathode ray to experiment with electrical charges and atoms. He found...

the particles in the beam were repelled by a negatively charged plate and attracted to the positively charged plate

• the particles must be negative because they are attracted to positive charges (opposites attract)
• Atoms are made up of even smaller particles
• positive mass of matter
• negative particle

Bohr wasn't incorrect, his information was just incomplete. He was right about there being different energy levels just not about the electrons orbiting at a fixed location/locations and speed.

Ernest Rutherford

1871-1937

• Experiment:
• beam of alpha particles (nuclear decay/uranium emits harmless, positive particles) is blocked by thin sheet of gold
• shoots alpha particles through sheet of gold
• Prediction:
• alpha particles would pass through gold
• some would be deflected but only slightly
• Actual Results:
• most particles did pass through
• however, some were deflected more than 90º

• Rutherford wasn't trying to disprove Thomson, he was trying to confirm Thomson's model
• His discovery was an accident
• it took Rutherford two years to come up with another model of the atom
• the atom is approximately a trillion times the volume of the nucleus

Preparatoria #15 Florida

Chemistry

Reporte #6

Juan Gerardo Ibáñez Ramírez

1678682

Grupo: 123

Fecha: 4/November/2013

Evolution of the Atomic Theories and Models