1 / 37

Unveiling the World of Atoms: From Ancient Theories to Modern Discoveries

Explore the evolution of atomic theory, from Democritus to modern scientists like Thomson and Rutherford. Learn about subatomic particles, isotopes, and the structure of the atom.

kferry
Download Presentation

Unveiling the World of Atoms: From Ancient Theories to Modern Discoveries

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter #3 ATOMS: The Building Blocks of Matter Chapter #3 • Atoms: The Building Blocks of Matter

  2. 3-1 Early Atomic Theory • Atoms are so small they cannot be observed directly. Scientists could use only experimental data to help describe the atom. • Around 400 B.C., Democritus (a Greek philosopher) suggested that the world was made of two things - empty space and tiny particles called atoms. Aristotle helped spread the word…neither backed by experimentation. • During the 1800's, a French Chemist (Antoine Lavoisier) discovered that chemical "changes" occurring in a closed system - the mass after a chemical change equaled the mass before the chemical change. • He proposed that, in ordinary chemical reactions, matter can be changed in many ways, but it cannot be created or destroyed (Law of Conservation of Mass). • Work by another French Chemist, Joseph Proust, had observed that specific substances always contain elements in the same ratio by mass (Law of Definite Proportions.)

  3. Foundations of Atomic Theory • Law of Definite Proportions: The elements composing a compound are always found in the same ratio by mass. • Law of Multiple Proportions: The masses of one element that combine with a fixed amount of another element to form more than one compound are in the ratio of small whole numbers. Example CO, CO2

  4. For example: Oxygen can combine with Carbon to form Carbon Monoxide, CO, or form Carbon Dioxide, CO2. • Dalton was the founder of Atomic Theory.

  5. Dalton’s Atomic Theory John Dalton, English schoolteacher • 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. • 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.

  6. NEW Modern Atomic Theory • Atoms are divisible into smaller pieces (protons, neutrons, electrons, and more). • Atoms of an element can have different masses (isotopes). • All matter is composed of atoms. • Atoms of any one element differ from atoms of another element.

  7. Section 3-2 • Atom- the smallest particle of an element that retains the chemical properties of that element. • Nucleus- is the positively charges, dense central portion of the atom that contains nearly all of its mass but takes up only an insignificant fraction of its volume.

  8. QUARKS equal in a neutral atom Atomic Number equals the # of... Most of the atom’s mass. Subatomic Particles ATOM NUCLEUS ELECTRONS NEUTRONS PROTONS NEGATIVE CHARGE POSITIVE CHARGE NEUTRAL CHARGE C. Johannesson

  9. Subatomic Particles

  10. Changing Subatomic Particles

  11. 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). e- have very tiny mass. • Most of the volume of the atom is empty space

  12. Famous Folks

  13. 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.

  14. Thomson was awarded the Nobel Prize in 1906 for his "discovery" of the first sub-atomic particle; the electron. This discovery strongly implied that Dalton was wrong and that the atom was not the smallest particle of matter. It looked as if the atom could be broken down into even smaller pieces, and to Thomson these smaller pieces were his negatively charged electrons.

  15. Conclusions from the Study of the Electron • 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

  16. 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.

  17. Discovery of the Electron • Robert Millikan later calculated the numerical charge of an electron to be 1.6 x 10 -19 Coulombs.

  18. 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

  19. Rutherford’s Findings • Most of the particles passed right through • A few particles were deflected • VERY FEW were greatly deflected Conclusions: • The nucleus is small • The nucleus is dense • The nucleus is positively charged

  20. Niels Bohr and the Bohr Model

  21. Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element. The number of protons = the number of electrons 6 C Carbon 12.011 Section 3-3

  22. Mass Number • Mass number is the number of protons and neutrons in the nucleus of an isotope. • Mass # = p+ + n • SOooo the number of Neutrons = • n= Mass # - p+

  23. Isotopes • Isotopes are atoms of the same element that have different masses. (number of neutrons)

  24. Nuclear Symbols 235 92 Mass number (p+ + n) Mass number (p+ + n) Element symbol Atomic number (# of p+) U 235 92

  25. Hyphen Notation Sodium-23 (23 is the mass #) Sooo… 23- 11 (atomic #) = 12 for the # of neutrons. 11 is the # of protons and electrons.

  26. Isotopes of H

  27. Amedeo Avogadroand the MOLE • 1 dozen =12 • 1 gross = 144 • 1 ream = 500 • 1 mole = 6.022 x 1023 • There are exactly 12 grams of carbon-12 in one mole of carbon-12.

  28. Calculations:Converting moles to grams • Given # of mole X ? g (look at periodic table)= g of 1 mole • How many grams of lithium are in 3.50 moles of lithium? • 3.50 mole X 6.941 g = 24.29 g Li 1 mol

  29. Calculations:Converting grams to moles • Given # of g X 1 mol = mol of g (look at periodic table) • How many moles of lithium are in 18.2 grams of lithium? • 18.2 g X 1 mol Li = 2.622 mol Li 6.941 g

  30. Avogadro’s Number • Is the number of particles in exactly one mole of a pure substance. • 6.022 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!

  31. Calculations:Converting Moles to Particles • Given # of mol x 6.022 x 1023 part= atoms 1 mol • How many atoms/particles/molecules of lithium are in 3.50 moles of lithium? • 3.50 mole X 6.022 x 1023 = 2.11 x 1024 atoms of Li 1 mol

  32. Calculations:Converting Particles to Moles • Given # of particles x 1 mole = mol 6.022 x 1023 • How many moles of lithium are there in 1.2044 x 1024 particles of Li? • 1.2044 x 1024 part x 1 mole = 2.0 mol Li 6.022 x 1023 part

  33. Calculations:Converting grams to particles • Given # of grams x 1 mol x 6.022 x 1023= particles ? g 1 mol • How many atoms/particles/molecules of lithium are in 18.2 g of lithium? • 18.2 g x 1 mol x 6.022 x 1023 = 1.58 x 1024 particle Li 6.941g 1 mol

  34. Calculations:Converting particles to grams • Given # of particles x 1 mol x ? g = g 6.022 x 1023 1 mol • How many grams are there in 8.02 x 1025 particles of lithium?

  35. Work Cited • “JJ Thomson”. Photo. July 28, 2006. http://www.sciencemuseum.org.uk/online/electron/section2/recording.asp • Cathode Ray Image and JJ Thomson Model. Image. July 28, 2006. http://www.brooklyn.cuny.edu/bc/ahp/LAD/C3/C3_Electrons.html • “Gold Foil Experiment”. Image. July 28, 2006. http://www.avon-chemistry.com/atom_lecture.html • “Rutherford”. Photo. July 28,2006. http://www.anthroposophie.net/bibliothek/nawi/physik/rutherford/bib_rutherford.htm • “Mole”. Photo. Aug 8, 2006. http://www.mwt.net/~bionorse/chemistry.htm

  36. “Hydrogen Isotopes”. Picture. August 4, 2006. www.sr.bham.ac.uk/xmm/atom.html • “Amedeo Avogadro”. avagadroc.jpg August 4, 2006. poohbah.cem.msu.edu/Portraits/PortraitsH... • “Uranium symbol”. Picture. August 4, 2006.www.webelements.com/webelements/scholar/... • Holt, Rinehart and Winston. Modern Chemistry. Harcourt Brace & Company. 1999. • “Atom Comic Cover”. Photo. Aug. 12, 2006. http://home.cfl.rr.com/fradford/Atom/Atom20.jpg

More Related