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Atomic Structure Democritus 460 BC ► Greek Philosopher ► Suggested world was made of two things – empty space and “atomos” Atomos – Greek word for uncuttable ►2 Main ideas Atoms are the smallest possible particle of matter There are different types of atoms for each material 2 John Dalton’s Atomic Theory 1804 1. All matter is made of atoms. 2. Atoms of one element are all the same. 3. Atoms cannot be broken down into smaller parts 4. Compounds form by combining atoms Dalton’s Early Atomic Model ► “Billiard Ball” model –viewed atoms as tiny, solid balls J.J. Thomson 1897 Discovered the electron He was the first scientist to show the atom was made of even smaller things JJ Thomson ► Used the Cathode ray tube to discover electrons Thomson’s Experiment Voltage source - + Vacuum tube Metal Disks Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source Passing + an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source Passing + an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source Passing + an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source Passing + an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source ►By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field he found that the moving pieces were negative Thomson’s “Plum Pudding” Model Democritus, Dalton, Thomson Video Ernest Rutherford *1912-1913 Discovered protons and the nucleus Ernest Rutherford ► He showed that atoms have (+) particles in the center and are mostly empty space ► He called the (+) particles protons ► He called the center of the atom the nucleus Rutherford’s Scattering Apparatus Alpha particles (+) bounce off of the positively-charged nucleus, but they go straight through the electron cloud. Rutherford’s Contribution ►The atom is mostly empty space. ►The nucleus is a small, dense core with a positive charge. Gold Foil video Rutherford’s Atomic Model Structure of the Atom ► Atom – smallest particle of an element that can exist alone Two regions of an atom ►Nucleus Center of atom Protons and neutrons ►Electron “cloud” Area surrounding nucleus containing electrons Structure of the Atom ► Proton – Positive charge (+), 1 atomic mass unit (amu); found in the nucleus amu -Approximate mass of a proton or a neutron ► Neutron – Neutral charge (0), 1 amu; found in the nucleus ► Electron – Negative charge (-), mass is VERY small Counting Atoms ► Atomic Number Number of protons in nucleus The number of protons determines identity of the element!! ► Mass Number (Atomic Mass) Number of protons + neutrons Units are g/mol Counting Atoms ► Isotopes Atoms of the same element with varying number of neutrons Different isotopes have different mass numbers because the number of neutrons is different Composition of the atom video Start at 3:25 Counting Atoms Nuclear Symbol Notation Atoms ► Protons have a positive (+) charge and electrons have a negative (-) charge ► In a neutral atom, the number of protons equals the number of electrons, so the overall charge is zero (0) Example/ Helium, with an atomic number of 2, has 2 protons and 2 electrons when stable Ions ► In a neutral atom Atomic number = # of protons = #of electrons ► Sometimes atoms will gain or lose electrons and form IONS ► Because an electron has a negative charge: When an atom GAINS electrons it becomes NEGATIVE When an atom LOSES electrons it becomes POSITIVE Ions Cation = a positive ion Anion = a negative ion Let’s Practice ► Aluminum (Al) (no periodic table) Protons = 13 Electrons = Neutrons = 14 Atomic Number = Atomic Mass = Let’s Practice w/ nuclear symbol notation ► Nuclear Symbol notation (no periodic table) Protons = Electrons = Neutrons = Atomic Number = Atomic Mass = Ag 108 47 Let’s Practice w/ isotopes ► use the periodic table Protons = Electrons = Neutrons = Atomic Number = Atomic Mass = Uranium-235 Let’s Practice with Ions Use the periodic table Charge = Protons = Electrons = Neutrons = Atomic Number = Atomic Mass = 39 K 1+