Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Take Good Notes! There is a quiz at the end…and you can use your notes. What is an atom? An atom is the smallest physical particle of an element that still retains the properties of that element. First scientist to suggest atoms: Democritus “Everything that is must be eternal.” Democritus believed that there were basic things that always exist, but can be rearranged; he called these “atomos”. At sea level, one cubic centimeter of air (size of a sugar cube, or marble) will have 45 billion atoms within it. ◦ 45,000,000,000,000,00 0,000 How many atoms would it take to fill a universe? All atoms are identical. Chemical reactions occur when atoms of one element are changed into atoms of another element. Law of Conservation of Mass Law of Constant Composition Law of Multiple Proportions Cr2O3 CrO3 What does an atom look like? One century after Dalton, Viennese scientist Ernst Mach wrote that “atoms cannot be perceived by the senses… they are things of thought.” Many scientists that made contributions to atomic structure – J.J. Thomson, Robert Millikan, Chadwick, Ernest Rutherford, and Neils Bohr, Schrodinger. 1. 2. 3. All elements are composed of tiny particles called atoms. Atoms of the same element are identical. Atoms of different elements are always different. Atoms of different elements can chemically combine in fixed ratios to form compounds. 4. Chemical reactions occur when atoms are joined, separated, or rearranged. Atoms of one element are NEVER changed into another during a chemical reaction. Atoms are solid and indivisible. Oil Drop Experiment 1908 Measured the charge on an electron. Electrons ◦ J.J. Thomson in 1897 ◦ Particles deflected in Cathode Ray tube ◦ Negative one charge ◦ Very small mass 1/2000 that of the lightest atom Thompson passed electric current through gases in a glass tube. The result was a glowing beam flowing from the negative side to the positive side. Glowing ray (cathode ray) was attracted to a positive magnet on the side of the tube. Beam must be negatively charged. Thompson hypothesized that all atoms had such negative charges within. (plum pudding model) Later, scientists proved that atoms contained both positive and negative charges (which balance each other out). Born in New Zealand. Terrible at mathematics. Diligent problem solver. First to discover the power of the atom, power to make bombs that could “make this old world vanish in smoke.” ◦ Ernest Rutherford 1911 ◦ Gold Foil Experiment using alpha particles ◦ nucleus Shot radioactive particles through a sheet of gold foil. Most went straight through, but others were knocked off course or bounced back. “Like shooting a fifteeninch shell at a sheet of paper and having it bounce off.” Nucleus – compact center of the atom where protons and neutrons are located Nucleus has very little of the atom’s volume, but contains most of the atom’s mass. Chadwick found that the mass of an atom is greater than the mass of protons plus electrons. Neutrons – portion of an atom with no charge Protons, neutrons, and electrons are called subatomic particles. Proton Mass equal to H Positive one charge Found in the nucleus Neutron Mass equal to H No charge Found in the nucleus Electron Mass 1/2000 of H Negative one charge “orbits” the nucleus Electrons orbit the nucleus in orbits, like a solar system. Planetary Model How do atoms differ? Atoms of different elements have different structures. Elements differ because their atoms contain different numbers of protons! Atomic Number – number of protons in the atom Electrons have negligible mass compared to protons and neutrons. Mass of a neutron is approximately equal to mass of a proton. Mass Number - number of protons plus number of neutrons in an atom. Beryllium – 5 neutrons ◦ Mass Number – ? Sodium – 12 neutrons ◦ Mass Number – ? Gold – 118 neutrons ◦ Mass Number = ? Atoms of the same element with different number of neutrons Chemically equivalent Most elements occur as a mixture of isotopes Mass of a proton is more than 1800 times the mass of an electron Spectrometer used to find masses of atoms Masses of subatomic particles too small to work with, so a reference isotope is used Mass Spectrometer Charged atoms fly towards a magnet. Where they hit the wall (detection screen) determines their mass. How many hit a certain spot determines the abundance (percent) of each isotope. magnet WALL One amu (atomic mass unit) is defined as 1/12 the mass of a Carbon-12 atom 1 amu is approx. equal to the mass of a proton or neutron Atomic masses found on periodic table are averages of all isotopes of that element Based on abundance (weighted mass) To calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance (expressed as a decimal), and then add the products. Chlorine is a mixture of Cl-35 and Cl-37. 75.77% Cl-35 (35) 24.23% Cl-37 (37) 0.7577 x 35 amu = 26.50 amu 0.2423 x 37 amu = 8.957 amu Added together… 35.45 amu + Carbon-12 Carbon-13 Atomic Mass? 98.89% 1.11% Silicon-28 Silicon-29 Silicon-30 Atomic Mass? 93.37% 4.63% 2.00% 1. What is an atom? 2. What is the symbol for… a) Calcium? b) Phosphorus? c) Potassium? d) Copper? e) Silver? f) Tin? g) Mercury? 3. What is the atomic number of… a) b) c) d) Lithium? Lead? Gold? Neon? 4. Describe Dalton’s atomic model. 5. Name the four premises of Dalton’s atomic theory. 6. Explain the difference between atoms and molecules. 7. Describe Thompson’s experiments and his atomic model. 8. Describe Rutherford’s experiments and his atomic model. 9. What is an atomic number? 10. Compare and contrast protons, neutrons, and electrons. 11. Chlorine-35? a) Mass Number? b)Number of Protons? c) Number of Electrons? d)Number of neutrons? 1. Atoms are the tiniest particle that retains an elements properties. 2. a) Ca 3. a) 3 b) P c) K d) Cu e) Ag f) Sn g)Hg b) 82 c) 79 d) 10 4. A solid mass, not divisible. 5. Name the four premises of Dalton’s atomic theory. 1. All elements are composed of tiny particles called atoms. 2. Atoms of the same element are identical. Atoms of different elements are always different. 3. Atoms of different elements can chemically combine in fixed ratios to form compounds. 4. Chemical reactions occur when atoms are joined, separated, or rearranged. Atoms of one element are NEVER changed into another during a chemical reaction. 6. Atoms – smallest part of an element that retains properties. Molecules - a group of atoms. 7. Thompson’s experiment – cathode ray tube found electron negative His atomic model – Plum pudding model 8. Rutherford’s experiment – gold foil experiment His atomic model – planatary model 9. Atomic number - the number of protons 10. Proton Mass equal to H Positive one charge Found in the nucleus Neutron Mass equal to H No charge Found in the nucleus Electron Mass 1/2000 of H Negative one charge “orbits” the nucleus 11. Chlorine-35? a) b) c) d) Mass # = 35 # of Protons = 17 # of Electrons = 17 # of neutrons = 18