Section 1- Discovering the parts of the atom
Chapter 7 Section 1- Discovering the parts of the atom
Early Ideas about matter
Greek Philosophers Aristotle ( BC) Matter made up of four Elements Fire, air, water, earth Democritus ( BC) Matter made up of small, solid objects that cannot Be created, destroyed or divided Called them atomos (English- atoms)
Democritus He had no way to test his ideas
His ideas did not conform to popular belief Therefore, he was not believed Aristotle was believed
John Dalton English school teacher and scientist- late 1700’s
Revised the idea of the atom Proposed the atomic theory All matter is made up of atoms that cannot be divided, created, or destroyed During chemical reaction, atoms of one element cannot be converted into elements of another element Atoms combine in specific ratios Atoms of one element are identical to each other but different from atoms of another element
Current theory Matter is made of atoms with empty space between and within them An atom is the smallest piece of an element that still represents the atom Atoms are very small 7.5 trillion carbon atoms could fit into a period at the end of a sentence Can be viewed with Scanning Tunneling microscope (STM) First observed in 1981
J.J. Thomson English Scientist ( 1856-1940) Studied cathode tubes
In his experiment- placed two plates on opposite sides of the cathode ray tube One plate was + charged while the other was – charged. The rays bent towards the + charged plate He concluded the cathode ray tube was – charged.
Thomson continued He conducted further experiments and found the particles had mass He proposed that these negatively charged particles came from the metal atoms in the electrode He called these particles electrons A particle with a – 1 charge He also proposed that atoms must contain + charged particles
Thomson cont. His model contained both positive and negative charges.
An atom was a sphere with positive charges spread throughout Negative charges were mixed with the positive charges Like chocolate chips in cookie dough
Rutherford Ernest Rutherford ( 1871- 1937) Student of Thomson
“Famous Gold Foil Experiment” He shot alpha particles which dense and positively charged at gold foil Most of particles bounced off the gold foil 1 In 10,000 hit the foil and bounced straight back
Rutherford’s Atomic Model
Since most of the alpha particles went straight through then the nucleus is mostly empty space Those that bounced and did not go in a straight direction hit something positive His Model says Most of the mass of an atom and the positive charge is in the center of an atom called the nucleus Protons are positively charged particles
Discovering Neutrons James Chadwick ( 1891-1974)
He determined that the nucleus also contained neutrons which are particles with no charge.
Bohr Model Niels Bohr ( 1885-1962)
There were limitations of Rutherford’s model He could not explain what the electrons were doing Bohr proposed that they move in circular levels or orbits around the nucleus
Modern Atomic Model Electrons form an electron cloud around the nucleus An electron cloud is an area around an atomic nucleus where an electron is most likely to be located
Quarks Protons and neutrons are made of smaller particles known as quarks 6 types of quarks Up, down, charm, strange, top, bottom
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