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Name: _________________________ Date: ___________________________ Grade 9 Chemistry Lesson 4 – The History of Atomic Theory Ancient Theories - The Greeks thought that all matter was composed of 4 elements: earth, air, fire and water. - These 4 elements would combine in different ratios to produce all the variety of substances we see today. - In ancient China, the elements were thought to be fire, water, wood, metal and earth. - Today we know there are over 100 elements that make up all the matter around us. Democritus - In 440 BCE, Democritus came up with a theory that as you broke down materials into smaller and smaller particles, eventually you would get a particle so small that you could not break it down further. He called this particle an atom. John Dalton - Dalton pictured atoms as small spheres with different properties. - He created a table of elements and created symbols to represent each one. - He created a 4 point theory to describe the nature of matter. 1. All matter is made of atoms. 2. All atoms of a certain element are identical in properties. 3. Atoms of different elements have different properties. 4. Atoms can combine to create new substances. J.J. Thompson - Using cathode ray tubes, he caused elements to give off a stream of negatively charged particles (electrons). - Since the elements did not have an overall charge, Thompson figured there must be positive particles in the atoms as well. - Thompson proposed that the atom is a positive mass with negative electrons inside it. - This is the raisin bun model. The electrons are negatively charged raisins in a positively charged bun. Ernest Rutherford - Discovered that protons are located in a central nucleus. Atoms had too much mass - Scientists had discovered that atoms weighed more than they should if there was only protons and electrons. - There were also isotopes of elements that weighed different amounts but had the same charge as a regular atom (eg. Lead 204 and lead 206). James Chadwick - Chadwick figured out there was another sub atomic particle called a neutron. The neutron added weight to the atom but had no charge. - Scientists then knew that there were protons and neutrons in the nucleus and electrons orbiting around it. Niels Bohr - scientists knew that when certain elements gained energy, they would release that energy only in very specific amounts. - Niels Bohr figured out that the electrons could only exist in specific orbits around the nucleus. - This led to the Bohr model of the atom. Quantum Mechanical Model - In this latest model of the atom, scientists have agreed that they cannot know exactly where an electron is or what momentum it has. - To continue using equations to calculate predictions based on their model of the atom, scientists have come up with a cloud of possible locations for the electrons based on the probability of an electron being in any one spot. Name: _________________________ Date: ___________________________ Grade 9 Chemistry Lesson 4 – The History of Atomic Theory Ancient Theories - The ______________ thought that all matter was composed of ____ elements: ________________, ________________, ________________ and ___________________. - These 4 ____________________ would combine in different __________________ to produce all the variety of substances we see today. - In ancient ____________________, the elements were thought to be ______________, __________________, ________________, __________________ and __________________. - Today we know there are over _________________ elements that make up all the matter around us. Democritus - In __________ BCE, ______________________ came up with a theory that as you broke down materials into smaller and smaller __________________, eventually you would get a particle so small that you could not break it down further. He called this particle an _____________________. John Dalton - ________________ pictured ______________ as small spheres with different properties. - He created a table of ___________________ and created ___________________ to represent each one. - He created a 4 point theory to describe the nature of matter. 5. All matter is made of _________________. 6. All atoms of a certain element are ______________________ in properties. 7. Atoms of different elements have ____________________ properties. 8. Atoms can _________________________ to create new substances. J.J. Thompson - Using cathode ray tubes, he caused elements to give off a stream of negatively charged particles (______________________). - Since the elements did not have an overall charge, Thompson figured there must be _______________________ particles in the atoms as well. - Thompson proposed that the atom is a positive ______________ with negative ________________________ inside it. - This is the __________________ _____________ model. The electrons are negatively charged ___________________ in a positively charged ________________. Ernest Rutherford - Discovered that ____________________ are located in a central ______________________. Atoms had too much mass - Scientists had discovered that atoms _____________________ more than they should if there was only _______________________ and _________________________. - There were also ________________________ of elements that weighed _________________________ amounts but had the ___________________ charge as a regular atom (eg. Lead 204 and lead 206). James Chadwick - _________________________ figured out there was another sub atomic particle called a _____________________. The neutron added ______________________ to the atom but had no __________________________. - Scientists then knew that there were _____________________ and _______________________ in the __________________________ and electrons ____________________________ around it. Niels Bohr - Scientists knew that when certain elements gained __________________, they would release that energy only in very ____________________ amounts. - Niels Bohr figured out that the ________________________ could only exist in specific ______________________ around the __________________________. - This led to the Bohr model of the atom. Quantum Mechanical Model - In this latest _________________ of the __________________, scientists have _________________ that they cannot know exactly where an _______________________ is or what _________________________ it has. - To continue using ______________________________ to calculate _________________________ based on their _________________________ of the atom, scientists have come up with a __________________________ of possible _____________________________ for the electrons based on the _________________________________ of an electron being in any one spot.
