The Structure of an Atom

1. The Structure of an Atom Chapter 3

2. Modern Atomic Theory

3. Greek Philosophers 4 Elements Air Fire Wind Water Democritus Atoms make up matter Aristotle Refuted Democritus and atom’s existence forgotten Early Theories

4. Modern Atomic Theory Deomcritus Atoms Differences in atoms

5. Dalton’s Atomic Theory • All matter is composed of extremely small particles called atoms. • All atoms of a given element are identical. • Atoms cannot be created, divided into smaller particles, or distroyed. • Different atoms combine in simple whole number ratios to form compounds. • In a chemical reaction, atoms are separated, combined or rearranged.

6. Dalton’s Atomic Theory • All matter is composed of extremely small particles called atoms. • All atoms of a given element are identical. • Atoms cannot be created, divided into smaller particles, or destroyed. (This part proven wrong) • Different atoms combine in simple whole number ratios to form compounds. • In a chemical reaction, atoms are separated, combined or rearranged.

7. Modern Atomic Theory Deomcritus Atoms Differences in atoms • Dalton • Atoms • Sameness • Created/destroyed • Combination • Rearragement

8. Cathode ray tube Stream of charged particles (electrons). See pg 60 for picture J. J. Thompson Used cathode ray tube to prove existence of electron. Proposed “Plum Pudding Model” Subatomic Particles and the Atom

9. Plum Pudding J. J. Thompson Plum Pudding Model Subatomic Particles and the Atom

10. Modern Atomic Theory Deomcritus Atoms Differences in atoms • Thompson • Atoms composed of electrons • Dalton • Atoms • Sameness • Created/destroyed • Combination • Rearragement

11. Gold Foil experiment Used to prove the existence of a positively charged core (Nucleus) The results were “like firing a large artillery shell at a sheet of paper and having the shell come back and hit you!” Ernest Rutherford

12. What should have happened Ernest Rutherford • What DID happened

13. Modern Atomic Theory Deomcritus Atoms Differences in atoms • Thompson • Atoms composed of electrons • Rutherford • Positively Charged Nucleus • Dalton • Atoms • Sameness • Created/destroyed • Combination • Rearragement

14. Subatomic Particles and the Atom • Chadwick • Worked with Rutherford. • Noted there was energy in the nucleus, but wasn’t the protons. • Concluded that neutral particles must aslo exist in nucleus. • Mosley • Assigned atomic number to atoms • Bohr • Designed “Bohr Model” of the atom.

15. Modern Atomic Theory Deomcritus Atoms Differences in atoms • Thompson • Atoms composed of electrons • Rutherford • Positively Charged Nucleus • Dalton • Atoms • Sameness • Created/destroyed • Combination • Rearragement • Chadwick • Neutrons exist in Nucleus

16. Subatomic Particles and the Atom • Three main particles: (see chart on pg 97) • Proton • Positive • In nucleus • Neutrons • Neutral • In nucleus • Electrons • Negative • Orbiting the nucleus (not inside)

17. Atomic Number Distinguishes one atom from another. = #p+ (& #e- for a neutral atom) Isotopes Differ in mass number Mass # = #p+ + #no Change is in # no Atomic Mass Unit Defined as 1/12 mass of a Carbon-12 atom p+ = 1 amu no = 1 amu e- = 0 amu Atomic Differences

18. Atomic Differences • Mass on the periodic table is based on the percent abundance of each isotope of that element. • Therefore it is a decimal. • Ex: Chlorine exist naturally as Cl-37 and Cl-35. Cl-37 is about 75% and Cl-35 is about 25%. So, (37 X .75) + (35 X .25) = 36.5 amu. • See Ex problem on pg 103 for more ideas.

19. Questions? • Ask now, or forever come in the morning for them!