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Atomic Theories Did Dan just realize beryllium’s metal? What did the element say when he got into a fight? Let me atom Democritus • Greek philosopher • the originator of a theory on atoms • He said atoms are the smallest indivisible bodies from which everything else is composed Dalton • Developed the first useful atomic theory • His theory was comprised of 4 postulates The postulates 1. All matter consists of tiny particles called atoms 2. Atoms are neither created nor destroyed (based on???) The postulates (cont.) 3. All atoms of a given element are identical and different from any other element 4. A given compound always has the same relative numbers and kinds of atoms J.J. Thomson • Discovered that the atom has a substructure using a cathode ray • Discovered a negatively charged particle and named it the electron Cont. • Couldn’t calculate the mass of an electron but figured out the ratio of its charge to its mass T-money cont. • His model is called the mint choc. chip model because • The atom was electrons surrounded by a soup of positive charge to balance the electron's negative charge, like chips surrounded by mint ice cream. Ernest Rutherford • Performed the gold foil experiment to discover the positively charged nucleus • He shot a beam of alpha particles at a piece of gold foil, while most went through, there were some that got scattered in every direction • Pg. 104 Are you Bohr’d yet? • Niels Bohr’s model depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus • Improvement on Rutherford's model Modern Atomic Theory • Nucleus lies in the center of the atom • Electrons do not orbit in welldefined paths, rather they can be predicted in an area called an electron cloud Something to break the monotony • When they broke open molecules, they found they were only stuffed with atoms. But when they broke open atoms, they found them stuffed with explosions. Subatomic Particles ProtonNeutron- ELECTRON- Proton • positive • found in the nucleus • has the mass of 1 amu Joke 1 • A Hydrogen atom runs up to two other atoms yelling and waving his arms. "Help! A mugger just stole my electron!" One of the other atoms looks him over and asks, "Are you sure?" The first replies: "I'm positive!" Neutron • Neutral • found in the nucleus • has the mass of 1 amu Joke 2 • A neutron walks into a bar and orders a drink. When he attempts to pay, the bartender looks at him and says, "For you, no charge." ELECTRON • Negative • found outside the nucleus • its mass is so small comparably that it is considered negligible Joke 3 • SUBATOMIC PARTICLE STORE The subatomic particle store had a sale last week. Electrons: $0.10 Protons: $0.10 Neutrons : free of charge Atomic Number • # of protons • Atoms are neutral so the # of protons must equal ________ • The whole number found in the element box Atomic Mass • Number of protons + number of neutrons • Measured in AMUs (Atomic mass units) • Where are the electrons? Isotopes • Atoms that have the same number of protons but different number of neutrons • Do isotopes have the same charge? • Do isotopes have the same masses? Isotope notation Isotope Notation decoded • "X" represents the atom's elemental symbol. • "A“--The mass number, (located in the upper left-hand corner) • "Z“-- The atomic number (found in the lower left-hand corner) Last joke • Q: What did the thermometer say to the graduated cylinder? • A: "You may have graduated but I've got many degrees"