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Honors Chemistry chapter 3

Honors Chemistry chapter 3. Atoms: The Building Blocks of Matter. PART 1. Icons of Early Atomic Theory. Icons in Early Atomic Theory. Democritus [400 B.C] Greek philosopher Hypothesized: Nature has a basic indivisible particle of which everything is made of Called this particle an atom

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Honors Chemistry chapter 3

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  1. Honors Chemistry chapter 3 Atoms: The Building Blocks of Matter

  2. PART 1 Icons ofEarly Atomic Theory

  3. Icons in Early Atomic Theory • Democritus [400 B.C] • Greek philosopher • Hypothesized: Nature has a basic indivisible particle of which everything is made of • Called this particle an atom • Greek “atomos” = indivisible

  4. 1790s – Discovery of Basic Laws • Law of Conservation of Mass • Mass is neither created nor destroyed during ordinary chemical reactions or physical changes • Law of Definite Proportions • A chemical compound contains the same elements in exactly the same proportions by mass regardless of size of sample or source of compound • i.e. Every sample of table salt is made of 39.34% Na and 60.66% Cl • i.e. H2O always has 2 atoms of H and 1 atom of O

  5. Basic Laws Continued • Law of Multiple Proportions • If two or more different compounds are composed of the same two elements then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers • i.e. CO and CO2 • CO = 1.00g of C and 1.33 g of O • CO2 = 1.00 g of C and 2.66 g of O • The ratio of the second element is 2.66 to 1.33 or 2 to 1

  6. Icons ofEarly Atomic Theory Continued • John Dalton [1808] • English schoolteacher – liked nature and weather • Developed: Dalton’s Atomic Theory

  7. 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 and are different from atoms of other elements • 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

  8. Issues withDalton’s Atomic Theory • Atoms can be split into even smaller particles (nuclear chemistry) and aren’t indivisible • i.e. nucleus, protons, electrons • A given element can have different masses • i.e. isotopes

  9. Structure of the Atom • Today’s definition of the atom • Atom = Smallest particle of an element that retains the chemical properties of that element • Two regions • Nucleus • Very dense, small center of the atoms • Protons and neutrons • Electron Cloud • Region occupied by electrons • Subatomic particles • Protons, neutrons, electrons

  10. Icons of Early Atomic Theory Continued • J.J. Thomson [1897] • Discovered: The 1st subatomic particle: the negatively charged electron • Used a Cathode Ray Experiment • Cathode Ray Tube – Electric current passed through a metal disk to another metal disk in a gas at low pressure (vacuum sealed tube) • i. e. neon signs and ‘old-fashioned’ television sets

  11. Cathode Ray Experiment • When a current passed through the cathode ray tube, the surface of the tube opposite the cathode glowed • Glow was hypothesized to be stream of particles called a cathode ray • Ray affected by magnetic fields • Attracted to positive charge • Deflected from negative charge • http://www.youtube.com/watch?v=7YHwMWcxeX8&NR=1

  12. Discovery of the1st subatomic particle • Thomson measured the ratio of the charge of the particles to their mass • Same ratio no matter what metal or gas was used • Named this particle an electron • http://www.youtube.com/watch?v=IdTxGJjA4Jw&feature=related

  13. Thomson’sPlum Pudding Model • Atoms are electrically neutral • Must have positive charges to balance the negatively charged electrons • Electrons have a lot less mass than atoms • Other particles must account for their mass • Plum Pudding Model • positively charged sphere with electrons dispersed through it

  14. Icons ofEarly Atomic Theory Continued • Robert Millikan [1909] • Discovered: The measurement of an electron charge • Oil Drop Experiment • Measured the difference in velocity of oil droplets • Charged droplets (ionizing radiation) vs. uncharged • http://www.youtube.com/watch?v=XMfYHag7Liw&feature=related

  15. Icons ofEarly Atomic Theory Continued • Ernest Rutherford (with Hans Geiger and Ernest Marsden) [1911] • Discovered: A new atomic model • Gold Foil Experiment • Bombarded thin piece of gold foil with alpha particles • Expected alpha particles to pass through with minimal deflection • Surprised when 1 in 8000 deflected back to source • It was “as if you had fired a 15 inch artillery shell at a piece of tissue paper and it came back and hit you” • http://www.youtube.com/watch?v=wzALbzTdnc8&feature=related

  16. Rutherford’sNew Model of the Atom • Discovered the nucleus is a small densely packed volume of positive charge • Size comparison • Nucleus = marble • Whole Atom = football field • At this point in history, we were not sure where the electrons were – stay tuned for more in Chapter 4

  17. PART 2 Inside the Atom

  18. Inside the Nucleus • 2 types of particles • Protons • positively charged = +1 • made up of quarks • Neutrons • neutral = 0 charge • Made up of quarks • Mass in the nucleus • Protons = 1.673 x 10-27 • Neutrons = 1.675 x 10-27 • To simplify, both have mass of 1 amu (atomic mass unit)

  19. How does the nucleus stay together? • Strong Nuclear Forces • Two protons extremely close = strong attraction • Two neutrons extremely close = strong attraction • Neutrons and Protons extremely close = strong attraction • Strong nuclear forces overcome the repulsion of like positive charges to keep the nucleus together!!!

  20. Where are the Electrons? • In the Electron Cloud • A cloud of negative charge outside of the nucleus • More on this later........ • Electrons = Negatively charged particles with almost no mass (9.109 x 10-31)

  21. Characteristics of Atoms • Atomic Number • Equal to the number of protons and specific to each type of element • Identifies the element • # of protons is what give that element its characteristic properties • Elements with different protons are NOT THE SAME ELEMENT!!!

  22. Neutral Atoms • Neutral atoms • total positive charge equals the total negative charge • # protons (+1 each) = # electrons (-1 each)

  23. Isotopes • Atoms of the same element (i.e. same # of protons) that have differing number of neutrons • Isotopes of the same element • have different masses • do not differ significantly in chemical behavior

  24. Mass Number • Mass number = #protons + # neutrons • Average Atomic Mass • Every element has isotopes • The periodic table takes into account all naturally occurring isotopes of an element and averages them

  25. Properties of Subatomic Particles

  26. Ions • Atoms with a charge • Negative – more electrons than protons • Positive – more protons than electrons • Charge = #protons - # electrons • Magnesium atom with 12 protons and 10 electrons has a charge of +2

  27. Average Atomic Mass • Average Atomic Mass listed on the periodic table • UNIT is amu = atomic mass unit • 1 amu is a standard • Equal to 1/12 the mass of a C-12 atom • Takes into account all an elements isotopes and the frequency of each isotopes occurrence in nature • How to Calculate Average Atomic Mass

  28. Example of Calculating the Average Atomic Mass – Hydrogen • There are two naturally occurring isotopes of hydrogen • Hydrogen with 1 proton and zero neutrons • Hydrogen with 1 proton and one neutron • Differentiating between the two isotopes (symbol – mass number) • Calculation:

  29. PART 3: The Mole

  30. Amadeo Avogadro • Amadeo Avogadro [1776] • Lawyer turned professor of mathematical physics • Theorized: equal volumes of all gases at the same temperature and pressure contain the same number of particles. • After Avogadro’s death Avogadro’s number was determined • Avogadro’s number is simply a unit of measure • 1 mole = 6.023 x 1023 of any substance • Typically used to talk about particles (atoms, compounds, etc.)

  31. The Mole Unitput into perspective!!! • One mole of rice grains is more grains than the total number of grains grown since the beginning of time. • A mole of rice would occupy a cube about 120 miles on each edge. • A mole of marshmallows would cover the US to a depth of 600 miles • A mole of hockey pucks would be equal in volume to the moon • A mole of basketballs would just about fit perfectly into a ball bag the size of the earth.

  32. Mole Video • http://www.youtube.com/watch?v=Hj83oRHdezc

  33. Mole Calculations • 1 mole = 6.02 x 1023 of anything (atoms, molecules, formula units, particles, etc.) • Use dimensional analysis when solving: • Conversion factor: 1 mole = 6.02 x 1023 atoms, particles, formula units, etc. • Practice: • If I have 3.5 moles of carbon atoms, how many molecules do I have? • If I have 5.43 x 1031 molecules of carbon dioxide, how many moles do I have?

  34. Molar Mass • Molar Mass • The mass of one mole of a substance • The molar mass of an element can be found on the periodic table • Same as the average atomic mass • 1 amu = 1 gram/mole • E.g. Average atomic mass of C = 12.011 amus • Molar mass of C = 12.011 grams/1 mole

  35. Calculations Using the Molar Mass – Use Dimensional Analysis • Calculate the number of grams of carbon in 3.25 moles of carbon. • Calculate the number of moles of hydrogen in 6.05 grams of hydrogen. • Calculate the number of atoms of carbon in 15.00 grams of carbon.

  36. Mole Sing A Long October 24, 2005

  37. It’s a Unit After All”http://www.youtube.com/watch?v=ZNnbZgnSohk • A mole of laughter, a mole of tears • A mole of atoms, a mole of cheer • The name of that measure • Is a real chemist’s treasure • It’s a unit after all • Chorus • It’s a unit, after all • It’s a unit, after all • It’s a unit after all • It’s a unit after all

  38. It’s a Unit After All” • http://www.youtube.com/watch?v=at_9A_gfln0 • A chemist’s friend, tried and ture, • An Avogadro would stand by you. • And any chemist anywhere, • Would stand up and swear, • It’s a unit after all • Chorus • It’s a unit after all, etc.

  39. “It’s a Unit After All” • Six point oh two times ten to twenty-three • A number to live by in chemistry • So this is October 24th • Don’t be absurd, for • It’s a unit after all • Chorus • It’s a unit after all • It’s a unit after all • It’s a unit after all • I’ts a unit after all

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