Atomic Theory.

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Atomic Theory

How did we know what matter is?
Different schools of thought in Ancient Greece: Aristotle had the idea that all matter was continuous and that matter’s characteristics were not independent but changeable Democritus had the idea that matter was made up of tiny indivisible particles that were surrounded by free space

What do we know about a chemical reaction?
reactants  products What’s happening to the matter in this process? When a solid (such as wood) is burned, where does the matter of the wood go? A chemical reaction is the transformation of one or more substances into one or more new substances

Law of Conservation of Mass
reactants  products What’s happening to the matter in this process? Law of conservation of mass: Mass is neither created nor destroyed during ordinary chemical reactions or physical changes

Law of Definite Proportions
Think of doubling a recipe: if one type of cake always needs 1 egg and 2 cups of sugar, two cakes of that variety will need 2 eggs and 4 cups of sugar, but it will be the same type of cake A chemical compound will contain the same elements in exactly the same proportions by mass regardless of the sample size or source of the compound. Think back to our SRQ, sucrose is always sucrose!

Law of Multiple Proportions
Think of modifying a recipe: if one type of cake always needs 1 egg and 2 cups of sugar, a different variety might need 2 egg and 2 cups of sugar, we’d say the second cake needs twice as many eggs as the first If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element (in relation to the mass of the first element) is a whole number

Dalton’s Atomic Theory
He wanted to explain the 3 laws of matter that had been observed All matter is composed of extremely small particles called atoms Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties

Dalton’s Atomic Theory
Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged.

Ob-scertainer You can’t see something, but you know it’s there… you feel it moving… How is it moving? Do your best to determine the movement of the “particle” in your containers

Ob-scertainer Solutions
#1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12

The Structure of the Atom
Even though Dalton was a little off, and it was discovered that atoms are divisible: An atom is the smallest particle of an element that retains the chemical properties of that element.

Discovery of the Electron
What are some relationships between matter and electricity? (where have you experienced electricity and how has matter been a part of this?)

Discovery of the Electron
Scientists used a cathode ray tube Inside was gas and two metal disks at each end of the tube (there was no vacuum or absence of matter) Electricity was passed through the tube They OBSERVED: A thin glowing stream formed between each metal end, starting at the cathode end.

Discovery of the Electron
Scientists used a cathode ray tube

Discovery of the Electron
Scientists used a cathode ray tube observed: The stream could be manipulated by magnetic fields The stream moved away from a negatively charged object The stream moved toward a positively charged object

Charge and Mass of the Electron
Millikan ran an experiment that allowed him to measure the charge of an electron He knew the mass of the droplets, and he knew the charge he was applying, From this, he was able to deduce the charge and mass of an electron Always use what you observe!

Charge and Mass of the Electron
Millikan ran an experiment that allowed him to measure the charge of an electron He knew the mass of the droplets, and he knew the charge he was applying, From this, he was able to deduce the charge and mass of an electron

New Model? Thomson proposed a new model for the atom to include the newly discovered electrons: The Plum Pudding Model

Discovery of the Atomic Nucleus
Rutherford and his associates: shot alpha particles (positively charged helium ions) at a sheet of gold foil. How do the masses of the alpha particles compare to the masses of gold atoms? Most particles managed to fly right through…

Discovery of the Atomic Nucleus
BUT some alpha particles were deflected to a ridiculous degree! Rutherford and his associates were not expecting this! It was as if the particles were dramatically repulsed by something If atoms were like the plum pudding model, how would they be deflected?

Discovery of the Atomic Nucleus
Rutherford concluded that the majority of an atom’s mass was densely packed positively charged protons and neutral neutrons located at the center of the atom Where were the electrons??

Discovery of the Atomic Nucleus
Bohr proposed a new model to replace the Plum Pudding model. His model proposed that an atom had a tiny nucleus of protons and neutrons and a large orbital of electrons, like how the planets orbited the sun.