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The Atom

The Atom. Section 4.1-4.3 Notes. History of Atomic Models. Democritus (~400BC) atomos = small, solid, indestructible particles of different shapes & sizes These were just ideas, not truly science… Dalton’s Atomic Theory Billiard Ball Model - small solid sphere

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The Atom

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  1. The Atom Section 4.1-4.3 Notes

  2. History of Atomic Models • Democritus (~400BC) • atomos = small, solid, indestructible particles of different shapes & sizes • These were just ideas, not truly science… • Dalton’s Atomic Theory • Billiard Ball Model - small solid sphere • Developed notion of conservation of mass and that atoms combine in specific ratios

  3. History of Atomic Models • J.J. Thomson • Plum Pudding Model - positive and negative particles dispersed throughout the atom • Used Cathode Ray tubes to discover the electron - first subatomic particle discovered!

  4. Cathode Ray Tube • A tube that contains a stream of electrons going from a negative disk (cathode) to a positive disk. • Deflected stream showed that electrons are negative.

  5. Rutherford • Nuclear or Planetary Model • Discovered dense positively charged nucleus of the atom while working with alpha particles • Gold Foil Experiment

  6. History of Atomic Models • Neils Bohr - • Also Solar System Model • Electrons travel in specific, circular orbits • Schrodinger & Heisenburg - • Quantum Mechanical Model • Dense nucleus w/ protons & neutrons • Electrons exist in ‘clouds’ called orbitals w/ specific energy levels • Mathematical predictions for probability of finding electrons • Electrons have particle and wave properties

  7. How big is the nucleus?!? Go to atoms videoclip

  8. Comparing subatomic particles…

  9. sToP & tHinK • If an atom has 2 protons and 2 neutrons, what is its atomic mass in atomic mass units (amu)? • What is the charge on an atom that has 7 protons and 7 electrons?

  10. Atomic Number • # of protons • # of electrons in a NEUTRAL atom • Always a whole number

  11. Mass Number • # of protons + neutrons • in atomic mass units (amu) • Isotopes - atoms of the same element with different masses • differ in number of neutrons • Examples: Carbon-13 & Carbon-14, Boron-10 & Boron-11 • Element-mass#

  12. Calculating # of neutrons • Subtract atomic # from mass # • Example: • Aluminum • 13 protons • 27-13 = 14 neutrons

  13. sToP & tHinK • What element has the atomic number 8? • How many protons, neutrons, and electrons are in a neutral atom of Potassium (K)? • How many protons, neutrons, and electrons are in a neutral atom of Boron-11?

  14. Relative Abundance • The atomic mass on the PT is the average of the isotopes for that element. • Example: Lithium has two isotopes, one has a mass of 6 amu & one has a mass of 7 amu. Lithium-7 occurs 92.5% of the time… • Multiply the mass by the abundance • Add the two together to get the atomic mass for the element • What is Lithium’s average atomic mass?

  15. sToP & tHinK • An element has two isotopes. One has a mass of 24 amu and represents 70% of the atoms of the element, the other has a mass of 25 amu and represents 30% of the atoms of the element. • What is the average atomic mass?

  16. sToP & tHinK • The published average atomic mass of phosphorus is 30.97. If it has two isotopes, phosphorus-30 and phosphorus-31, which one is more abundant. Explain.

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