11 The Atomic Nature of Matter

1. 11 The Atomic Nature of Matter • atoms • Molecules • Chemicals & matter • Homework: • RQ: 6, 8, 11, 13, 14, 18, 22, 23, 24. • Ex: 2, 3, 8, 9, 17, 19, 27.

2. The Atomic Hypothesis Consider the following process: Smash a rock Smash the pieces Continue till rough powder Grind the powder indefinitely When does the process stop? Is it still rock when you are done?

3. Atomic History • Hypothesized in 5th Century B.C. (Greece) • Aristotle 4th Century B.C. did not believe in atoms. Taught 4-element idea (earth, air, water, fire) • Dalton 1800s England revived atomic idea • Brown 1827 hypothesized atoms caused oscillation of microscopic particles • Today we know 88 naturally occurring atoms and about 30 more lab created

4. Unicellular Algae Light Microscope SEM, about 100 times better resolution (SEM) Electron Microscope

5. Resolution is Related to Wavelength of the Waves Objects larger than distance between waves leaves a clear “shadow”. Objects smaller than distance between waves do not. Shorter waves give us more “resolution”

6. Atoms • years of experimentation led to a rough model: our own solar system, which is mostly empty space. • “middle” of the atom is nucleus • “outside” of atom is an electron shell

7. The Nucleus and the Atom • nucleus: “protons” and “neutrons” • each of similar size and mass • proton has positive charge • neutron has no charge • electrons have negative charge and are much less massive

8. element • substance in which each atom has the same number of protons (neutrons may vary) • atomic number = # protons in atom • mass number = # protons + # neutrons • isotopes have same # protons but with varying # neutrons. Example: • Hydrogen: 1 proton, 0 neutron, 1 electron • isotope: 1 proton, 1 neutron, 1 electron

9. chemical properties • depends on number of electrons which must equal number of protons for uncharged atom. • atoms with more (or less) electrons than protons are called “ions” and have different chemical behavior.

10. Periodic Table • elements in same column have similar chemical properties due to similar electronic structure. • major groups: metals, metalloid, non-metal • symbols are used to label the different atoms. • some symbols come from different languages e.g. gold = Au, silver = Ag, etc.

11. The Periodic Table of The Elements (the distinct atoms)

12. Molecules Molecules are groups of atoms. Here are a few examples. oxygen ammonia methane water

13. Terminology • Element – atoms with the same number of protons. • Molecule – smallest particle of chemical substance that has the same composition and chemical properties, e.g. water molecule. • Compound – chemical substance formed from 2 or more elements and which has a definite chemical formula. Note that crystals such as NaCl are not molecular. • Mixture – substance with components that have not combined chemically. • Chemical Substance - an element, compound, or mixture.

14. A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions.

15. Summary • atoms make up matter, atoms are: protons, neutrons, electrons, type of atom determined by # protons. • molecules are formed from atoms • atomic and molecular structures determined by electron microscopy • definitions: element, mixture, isotope, compound, substance. • periodic table: columns have similar chemical properties.