Dalton’s Theory – Explains the Law of Conservation of Matter Atoms are separated, combined or rearranged in a reaction, they are not created, destroyed or divided.
What is an atom? The smallest particle of an element that retains its original properties
Discovering the Existence of the Electron – JJ Thompson p. 104 Cathode Ray Tube – Led to the TV
Particles had a negative charge. Rays consisted of particles. All types of gases and cathodes produced a beam of particles. P. 104-105 P. 122 Q 38, 39 P. 123 Q 70
JJ Thomson – 1890s Found that the mass of the particle in the cathode ray tube was smaller than the mass of the Hydrogen atom. Which part of Dalton’s theory did he prove wrong? X
Eugen Goldstein (1886) – discovered another ray that traveled in the opposite direction of the cathode ray Positively charged particles (proton) Called canal rays Page 106
If electrons are part of all matter and they possess a negative charge, why is matter neutral? If the mass of an electron is so small, what accounts for the rest of the mass in an atom? More Questions
JJ Thomson’s Answer – Plum Pudding ModelPlum Pudding Model P. 122 - 42
Ernest Rutherford’s Experiment Ernest Rutherford’s Experiment – 1911 p. 107
Evidence Contradicts the Plum Pudding Model Rutherford Concluded: 1.Atoms consist mainly of empty space in which electrons move freely. 2.A tiny dense space in the center of the atom (nucleus) contains the majority of the mass and the positive charges. 3.The positive charge of the nucleus holds the negative electrons within the atom. P. 123 Q-58, P. 124 Q-74
If electrons are part of all matter and they possess a negative charge, why is matter neutral? 1st Question Answered
Protons and Neutrons p. 107 Rutherford (1920) –Protons are positively charged and found in the nucleus James Chadwick (1932) –Neutrons are found in the nucleus, has no charge and has a mass equal to the proton Space Between Atoms - Video P. 124 Q - 76
Second Question Answered: If the mass of an electron is so small, what accounts for the rest of the mass in an atom?
What do atoms look like? Silicon Atoms How can we take pictures of atoms?- Video
Atomic Number p. 110 Henry Moseley Each element has a unique positive charge Equal to # of Protons and Electrons in a neutral atom. P. 122 Q - 46
Mass Number and Atomic Number p. 111 Mass number = protons + neutrons 12 3 1 H 1 H 1 H Protium DeuteriumTritium Mass number Atomic number 1 proton 1 neutron 1 proton 2 neutrons Isotopes – atoms with the same number of protons and electrons,but a different number of neutrons P. 122 Q – 49, 51, 52 P. 123 Q - 72
Atomic Mass Unit p. 114 1 AMU = 1/12 the mass of the Carbon Atom 1 AMU ≠ mass of a proton or a neutron
Average Atomic Mass p. 114-116 Chlorine-35 (34.969 amu x 75.770%) Chlorine-37 + (36.966 amu x 24.230%) 35.453 amu P. 122 Q - 53
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