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Chemistry Chapter 3 Unit 4

Chemistry Chapter 3 Unit 4. Atoms: The Building Blocks of Matter. Law of Conservation of Mass. Mass is neither created nor destroyed during chemical or physical reactions. Total mass of reactants = Total mass of products. Antoine Lavoisier. Dalton’s Atomic Theory (1808).

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Chemistry Chapter 3 Unit 4

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  1. Chemistry Chapter3Unit 4 Atoms: The Building Blocks of Matter

  2. Law of Conservation of Mass Mass is neither created nor destroyed during chemical or physical reactions. Total mass of reactants = Total mass of products Antoine Lavoisier

  3. Dalton’s Atomic Theory (1808) • All matter is composed of extremely small particles called atoms • Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties John Dalton • Atoms cannot be subdivided, 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

  4. Modern Atomic Theory Several changes have been made to Dalton’s theory. Dalton said: Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties Modern theory states: Atoms of an element have a characteristic average mass which is unique to that element.

  5. Isotopes Elements occur in nature as mixtures of isotopes. Isotopes are atoms of the same element that differ in the number of neutrons, thus changing the atomic mass.

  6. Atomic Masses Atomic mass is the average of all the naturally isotopes of that element. Carbon = 12.011 Hyphen Nuclear 6 6 6

  7. Subatomic comparison e

  8. Modern Atomic Theory #2 Dalton said: Atoms cannot be subdivided, created, or destroyed Modern theory states: Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions!

  9. Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

  10. Some ModernCathode Ray Tubes

  11. Thomson’s Atomic Model Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

  12. Mass of the Electron 1909 – Robert Millikan determines the mass of the electron. The oil drop apparatus Mass of the electron is 9.109 x 10-31 kg

  13. Conclusions from the Study of the Electron • Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons. • Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons • Electrons have so little mass that atoms must contain other particles that account for most of the mass

  14. Rutherford’s Gold Foil Experiment • Alpha particles are helium nuclei • Particles were fired at a thin sheet of gold foil • Particle hits on the detecting screen (film) are recorded

  15. Try it Yourself! In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

  16. The Answers Target #1 Target #2

  17. Rutherford’s Findings • Most of the particles passed right through • A few particles were deflected • VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions: • The nucleus is small • The nucleus is dense • The nucleus is positively charged

  18. Atomic Particles

  19. The Atomic Scale • Most of the mass of the atom is in the nucleus (protons and neutrons) • Electrons are found outside of the nucleus (the electron cloud) • Most of the volume of the atom is empty space “q” is a particle called a “quark”

  20. The Quark… Oops…wrong Quark!

  21. About Quarks… Protons and neutrons are NOT fundamental particles. Protons are made of two “up” quarks and one “down” quark. Neutrons are made of one “up” quark and two “down” quarks. Quarks are held together by “gluons”

  22. Atomic Number Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

  23. Isotopes…Again (must be on the test) Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.

  24. Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope. Mass # = p+ + n0 18 8 8 18 Arsenic 75 33 75 Phosphorus 16 15 31

  25. The Mole 1 dozen = 12 1 gross = 144 1 ream = 500 1 mole = 6.02 x 1023 There are exactly 12 grams of carbon-12 in one mole of carbon-12.

  26. Avogadro’s Number 6.02 x 1023 is called “Avogadro’s Number” in honor of the Italian chemist Amadeo Avogadro (1776-1855). I didn’t discover it. Its just named after me! Amadeo Avogadro

  27. Calculations with Moles:Converting moles to grams How many grams of lithium are in 3.50 moles of lithium? 3.50 mol Li 6.94 g Li = 24.29 g Li 1 mol Li

  28. Calculations with Moles:Converting grams to moles How many moles of lithium are in 18.2 grams of lithium? 18.2 g Li 1 mol Li = mol Li 2.62 6.94 g Li

  29. Practice Calculations • How many moles of Mg are in 45.7 g of Mg? • How many moles of C are in 100.0g of C? • How many moles of O are in 75.98 g of O? • How many moles of N are in 274.8 g of N? • How many moles of K are in 355.0 g of K? • How many moles of Ag are in 8 g of Ag? • How many moles of Hg are in 0.98 g of Hg? 1.88g 8.33g 4.75g 19.61g 9.08g 0.074g 0.0049g

  30. Calculations with Moles:Using Avogadro’s Number How many atoms of lithium are in 3.50 moles of lithium? 3.50 mol Li 6.022 x 1023 atoms Li = atoms Li 2.11 x 1024 1 mol Li

  31. Practice calculations • How many atoms of Mg are in 5 moles of Mg? • How many atoms of C are in 16 moles of C? • How many atoms of O are in 24 moles of O? • How many atoms of N are in 58.98 moles of N? • How many atoms of K are in 45.50 moles of K? • How many atoms of Ag are in 32.25 moles of Ag? • How many atoms of Hg are in 15.0 moles of Hg? 3.01x 1024 9.063 x 10 24 1.44 x 1025 3.55 x 1025 2.74 x 1025 1.94 x 1025 9.03 x 1024

  32. Calculations with Moles:Using Avogadro’s Number How many atoms of lithium are in 18.2 g of lithium? 18.2 g Li 1 mol Li 6.022 x 1023 atoms Li 6.94 g Li 1 mol Li (18.2)(6.022 x 1023)/6.94 = atoms Li 1.58 x 1024

  33. Practice Calculations • How many atoms of Mg are in 45.7 g of Mg? • How many atoms of C are in 100.0g of C? • How many atoms of O are in 75.98 g of O? • How many atoms of N are in 274.8 g of N? • How many atoms of K are in 355.0 g of K? • How many atoms of Ag are in 8 g of Ag? • How many atoms of Hg are in 0.98 g of Hg?

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