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Atomic Model Review ( Match Theory to Scientist)

1. Atoms are solid spheres. 2. Electrons move around the nucleus in specific levels. 3. Protons are concentrated in the center. 4. Electrons move in ever-changing paths within certain energy levels. 5. Electrons are stuck in the atom’s surface. Thomson Dalton C. Bohr D. Rutherford

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Atomic Model Review ( Match Theory to Scientist)

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  1. 1. Atoms are solid spheres. 2. Electrons move around the nucleus in specific levels. 3. Protons are concentrated in the center. 4. Electrons move in ever-changing paths within certain energy levels. 5. Electrons are stuck in the atom’s surface. Thomson Dalton C. Bohr D. Rutherford E. Electron cloud model Atomic Model Review(Match Theory to Scientist) Mullis

  2. Atomic Number • Number of protons or electrons in an element • Identifies the element • Atomic Mass • Nucleus contains most of the mass of an atom. • Protons and neutrons are each ~ 1.67 x 10-24 g. • Electrons are each ~ 9.11 x 10-28 g. • Use atomic mass unit (amu) instead of gram. • The mass of one proton is ~ 1 amu. • Mass Number • The sum of the number of protons and number of neutrons in the nucleus • Is approximately equal to the average atomic mass shown on periodic table. • Number of neutrons = mass number – atomic number Mullis

  3. Isotopes • Atoms of the same element with different numbers of neutrons • Have the same number of protons • Example: Carbon-12 and Carbon-14 • Radioactive Isotopes • Unstable in nature • Atoms with a neutron: proton ratio of > 1.5:1 are unstable. • Can be used to date fossils and rocks • The time it takes for half of the radioactive atoms in a piece of the fossil to change to another element is its half-life. Mullis

  4. Radioactive Isotopes If 25% of the atoms in a rock are uranium-238, how old is the rock? • 50% changed to lead-206 in 4.510 x 109 yrs • 50% of remaining changed to lead-206 in4.510 x 109 yrs • Total is 75% changed in 9.020 x 109 yrs • Age of rock is ~ 9,020 million years Mullis

  5. The Atom: Idea to Theory • Democritus (~ 400 BC) called nature’s basic particle an atom • Atom comes from Greek word meaning “indivisible” • 1808: Dalton proposed a theory with several statements which were later verified, but his “model” of an atom was that of a sphere. Mullis

  6. Modern Atomic Theory • Democritus = Idea about an atom • Dalton = Scientific theory which could be tested • Dalton’s concepts which have “held true:” • All matter is composed of atoms • Atoms of any one element differ in properties from atoms of another element Mullis

  7. John Dalton • Reinstated atomic theory into western science, composed 4 postulates and 3 laws to explain the atom as he found them to be, and explained that the atom is the smallest amount of an element to retain its basic properties.

  8. Dalton’s Atomic Theory • All matter is composed of extremely small particles called atoms. • Atoms of a given element are identical in size, mass and other properties. • Atoms cannot be divided, created or destroyed. • Atoms of different elements combine in simple whole-number ratios to form chemical compounds. • In chemical reactions, atoms are combined, separated or rearranged. Mullis

  9. Law of Definite Proportions: • A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample. • Law of Conservation of Mass : Mass is neither created nor destroyed during ordinary physical or chemical changes. • Law of Multiple Proportions: • If two or more different compounds are made of the same two elements, then the ratio of the masses of the 2nd element combined with a certain mass of the 1st element is always a ratio of small whole numbers. Mullis

  10. J.J. Thomson • Experimented with cathode rays and found that the properties didn’t change. Based on similar experiment results, he distinguished charges within atoms, positive and negative charges, which he explained in his plum-pudding model. Thomson also found the ratio for electrons’ charge.

  11. J. J. Thomson (1856-1940) • He is credited with discovering the electron • He constructed a cathode ray tube so that he could quantitatively measure the effects of electric and magnetic fields on the thin streams of electrons passing through the positively charged electrode http://en.wikipedia.org/wiki/J.J._Thompson http://en.wikipedia.org/wiki/J.J._Thompson

  12. Ernest Rutherford • Revealed three types of radiation: alpha, beta and gamma. He found gamma radiation to be high energy radiation like X rays, and discovered that positively charged alpha particles combined with electrons to make helium. Rutherford concluded that alpha particles were helium nuclei and that the nucleus of an atom contains positive particles. He later came to the conclusion that electrons circle the nucleus when he performed an experiment by shooting a stream of particles through a sheet of gold foil and measured the angles of the particles’ deflections.

  13. Ernest Rutherford (1871-1937) • He discovered the protonandproposedthe idea of a nucleus with his gold foil experiment. • He discovered three types of radiation: alpha, beta, and gamma • His discoveries led to the downfall of J.J. Thompson’s “plum-pudding” model of the atom http://en.wikipedia.org/wiki/Ernest_Rutherford

  14. James Chadwick • James Chadwick was onto neutrons when he saw in experiments like Rutherford’s that some of the particles were deflected backwards, meaning that they had no charge. Chadwick had discovered the neutron! neutron

  15. The Mole • A mole is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12. • A mole is the SI unit for the amount of a substance. Mullis

  16. Avogadro’s Number • This is the number of particles in one mole. • Avogadro was an Italian scientist who explained the relationship between mass and number of atoms. • 12.0 g of carbon-12 contains 6.022 1367 x 1023 carbon-12 atoms. Avogadro’s number is rounded to 6.022 x 1023 Mullis

  17. Molar mass • The mass of one mole of a pure substance • Units = __g_ mol Molar mass of an element = atomic mass of the element in amu. Molar mass of Al is 26.98 g/mol Mullis

  18. Relationship between mass, moles and molecules in a compound Mullis

  19. Molar mass • Molar mass of a substance = mass in grams of one mole of the substance. • A compound’s molar mass is NUMERICALLY equal to its formula mass. 2 mol H x 1.01 g H = 2.02 g H 1 mol H 1 mol O x 16.00 g O = 16.00 g O 1 mol O molar mass H2O = 18.02 g/mol • Formula mass H2O = 18.02 amu • Molar mass H2O = 18.02 g/mol Mullis

  20. Molar Mass Example What is the molar mass of K2SO4? 2 mol K x 39.10 g K = 78.20 g K 1 mol K 1 mol S x 32.10 g S = 32.07 g S 1 mol S 4 mol O x 16.00 g O = 64.00 g O 1 mol O molar mass K2SO4 = 174.27 g/mol How many moles of each element are present in this compound? 2 mol K, 1 mol S, 4 mol O Mullis

  21. What is the molar mass of C6H12O6? 6 mol C x 12.01 g C = 72.06 g C 1 mol C 12 mol H x 1.01 g H = 12.12 g H 1 mol H 6 mol O x 16.00 g O = 96.00 g O 1 mol O molar mass C6H12O6 = 180.18 g/mol How many moles of each element are present in this compound? 6 mol C, 12 mol H, 6 mol O Mullis

  22. Converting to grams from moles How many moles of glucose are in 4.15x10-3 g C6H12O6? 4.15x10-3 g x 1 mol C6H12O6= 2.30 x 10-5 mol C6H12O6 180.18 g How many molecules of glucose are in 4.15x10-3 g C6H12O6? 2.30 x 10-5 mol C6H12O6x 6.022 x 10 23 molecules = 1 mol (2.30 x 6.022)(10(-5+23)) = 13.90 x 10 –18 molecules = 1.39 x 10 –19 molecules Mullis

  23. What is the mass in grams of 6.25 moles copper (II) nitrate? Cu 2+ NO3 - : formula isCu(NO3)2 Find molar mass of Cu(NO3)2first. 1 mol Cu x 63.55 g Cu = 63.55 g Cu 1 mol Cu 2 mol N x 14.01 g N = 28.02 g N 1 mol N 6 mol O x 16.00 g O = 96.00 g O 1 mol O molar mass Cu(NO3)2 = 187.57 g/mol Now find mass in grams of 6.25 moles: 6.25 moles x 187.57 g= 1172 g Ans. 1170 g Cu(NO3)2 1 mol Mullis

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