2 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 changeableDemocritus had the idea that matter was made up of tiny indivisible particles that were surrounded by free space
3 What do we know about a chemical reaction? reactants productsWhat’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
4 Law of Conservation of Mass reactants productsWhat’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
5 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 cakeA 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!
6 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 firstIf 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
7 Dalton’s Atomic Theory He wanted to explain the 3 laws of matter that had been observedAll matter is composed of extremely small particles called atomsAtoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties
8 Dalton’s Atomic Theory Atoms cannot be subdivided, created, or destroyedAtoms of different elements combine in simple whole-number ratios to form chemical compoundsIn chemical reactions, atoms are combined, separated, or rearranged.
9 Ob-scertainerYou 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
11 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.
12 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?)
13 Discovery of the Electron Scientists used a cathode ray tubeInside 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 tubeThey OBSERVED: A thin glowing stream formed between each metal end, starting at the cathode end.
14 Discovery of the Electron Scientists used a cathode ray tube
15 Discovery of the Electron Scientists used a cathode ray tube observed:The stream could be manipulated by magnetic fieldsThe stream moved away from a negatively charged objectThe stream moved toward a positively charged object
16 Charge and Mass of the Electron Millikan ran an experiment that allowed him to measure the charge of an electronHe 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 electronAlways use what you observe!
17 Charge and Mass of the Electron Millikan ran an experiment that allowed him to measure the charge of an electronHe 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
18 New Model?Thomson proposed a new model for the atom to include the newly discovered electrons:The Plum Pudding Model
19 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…
20 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 somethingIf atoms were like the plum pudding model, how would they be deflected?
21 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 atomWhere were the electrons??
22 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.