1. The Atom Chapter 8 Great Idea: All of the matter around us is made of atoms, the chemical building blocks of our world

2. Chapter Outline The Smallest Pieces The Structure of the Atom When Matter Meets Light The Periodic Table of the Elements

3. The Smallest Pieces

4. Democritus –Cut matter to reach smallest piece –Called “the atom” or “uncuttable” –All material formed from atoms

5. Elements John Dalton –Father of modern atomic theory –Cannot break down elements –Elements composed of atoms Example: Water Molecule is 1 oxygen atom and 1 hydrogen atom

6. Are Atoms Real? Evidence for the reality of atoms –Behavior of a gas –Chemical combinations –Radioactivity –Brownian motion –X-ray crystallography –Atomic-scale microscopy

7. The Behavior of a Gas Bernoulli –atoms have mass & velocity and thus kinetic energy Decreasing volume increases pressure (A) Increasing temperature increases pressure (B) A B

8. Chemical Combinations Dalton applied law of definite proportions –Elements combine in a specific ratio of weights Ex: Water is 8 parts oxygen to 1 part hydrogen Ratio of weights is a small whole number –Ex: 12 lbs Carbon can combine with either 16 lbs or 32 lbs of oxygen Implication: some units of elements are fundamentally indivisible

9. Radioactivity Phosphors flash when hit by radiation 1903 demonstrated the twinkling caused by this effect

10. Brownian Motion Brownian motion: erratic, jiggling motion –pollen grains suspended in water Einstein: motion is random collisions of atoms –Predicted particle movement Perrin tested and confirmed Einstein’s predictions

11. X-ray Crystallography Developed in 1912 Demonstrates arrangement of atoms in crystals

12. Discovering Chemical Elements Electrolysis Mendeleev Current Periodic Table –112 elements 92 found in nature Everyday elements –Helium, carbon, aluminum, copper, gold

13. The Structure of the Atom

14. Thomson identified electron –Negatively charged –Smaller and lighter than smallest atom Atoms are NOT fundmental building blocks, but are made up of smaller more fundamental particles

15. The Atomic Nucleus Rutherford determined atomic structure Concluded – atom has nucleus at center surrounded by electrons Later discoveries found nucleus is composed of protons and neutrons Most particles traveled through foil Some deflected

16. Why the Rutherford Atom Couldn’t Work Why? –Object in circular orbit is accelerating –Accelerated electrical charge emits electromagnetic radiation –Electrons giving off energy while orbiting Result: electrons spin toward nucleus eventually atom ceases to exist Rutherford atom exists <1min

17. When Matter Meets Light

18. The Bohr Atom First working model of atom Energy levels for electrons –Specific distances from nucleus –Electrons exist with no radiation –Electrons cannot exist between allowed distances (energy levels)

19. Example Figure 8-7 Lowest energy level Any level above ground state Energy changes when level changes

20. Photons: Particles of Light Used to move electron to higher energy state Photon emitted as electron moves to lower energy state

21. Photons cont. Quantum leap or jump-electron disappears from original location and reappears in final location-never at positions in between Energy is equal

22. Energy in Bohr atom Energy required to leave ground state –Absorb photon –Heat Increases collisions

23. Spectroscopy Atoms emit and absorb different photons Depends on differences between energy levels Each atom has distinct set of photons Spectrum: all photons emitted by an atom –Used for identification

24. Spectroscopy cont. Light from gaseous atoms is spread out by passing through a prism

25. Spectroscopy cont. Each atom produces a unique set of lines-the atomic fingerprint

26. The Periodic Table of the Elements

27. Periodic Table of the Elements Systematizes elements Columns contain similar elements soft, silvery elements all colorless, odorless inert gases

28. Why the Periodic Table Works: Electron Shells Patterns mirror arrangement of electrons in shells Pauli exclusion principle First shell 2 electrons, second shell 8 etc.