Intensive Chemistry Day 1: The Structure of Matter

1. Intensive ChemistryDay 1: The Structure of Matter Katy Johanesen Ph.D. Candidate, USC Department of Earth Sciences

2. Introduction • I am a geologist • I study the chemical reactions and physical changes in rocks and what they can tell us about the past, about plate tectonics, and about processes like earthquakes and volcanoes. • Chemistry is vital to my research! Questions? Email johanese@usc.edu

3. Today’s lecture has two parts Atoms Molecules and Compounds

4. The Atom • Name comes from the greek word atoma, or "indivisible particles“ –Democritus • This idea fell out of favor, Aristotle’s four elements became popular: • earth, wind, fire , and water • Robert Boyle later disproved this in the 1600’s http://atomictimeline.net/index.php for a full timeline of atom discoveries

5. The atom is made up of even smaller particles Protons – positive charge Neutrons – no charge Electrons – negative charge Cathode ray tube experiment - discovery of the electron: electrons in the form of electricity flow from one end of the tube to the other. Watch what happens when a magnet comes near the tube. Which side of the magnet do you think they used? Source: http://chem.illinois.edu/CLCwebsite/demos.html

6. Emission Spectroscopy • Each element emits different wavelengths of light (energy) when • Niels Bohr explained this with a new model of the atom!

7. Bohr model of the Atom • Electrons are organized into energy levels or shells, also called orbitals • Energy is absorbed when an e- moves out a level, and emitted when it moves in. Outermost shell = valence electrons

8. Schrӧdinger Model of the Atom • Electrons have properties of both particles and waves • Orbitals represent probability of where the electron will be (two e- in each orbital)

9. The Elements • Each element has a unique atomic number • Atomic number = number of protons • Each atom has an equal number of electrons • Atoms with the same # protons but different # neutrons are called Isotopes • Periodic Table of the Elements: www.ptable.com

11. Bonding • Atoms can combine to form compounds or molecules • Ionic – give and take electrons (NaCl) • Covalent – sharing (C) • Metallic – positive ions in a sea of valence electrons (Au, Cu) • Hydrogen bonds (weak) • Van der Waals bonds… we won’t talk about these.

12. Ionic Bonds • Atoms donate or accept valence electrons and become ions, or charged particles • Na loses one e- and forms Na1+ • Cl gains one e- and forms Cl1- • The charged ions attract each other and form NaCl • Most common for alkali and alkali earth metals (+), halogens (-), and some transition and post-transition metals like Fe and Al.

13. Na (Sodium) and Cl (Chlorine)

14. Na (Sodium) and Cl (Chlorine) + -

15. NaCl (table salt) crystals Source: http://www.sciencephoto.com

16. Covalent Bonds • Atoms share valence electrons in a hybrid orbital between them • Two atoms of O each need two valence electrons to complete their outer shell, so they bond together to form O2 • Most common for nonmetals like C, O, N, P, S, and H. Halogens also form covalent bonds with each other.

17. O (Oxygen): atomic number 8

18. O2 Note: only two electrons from each atom are shared, not all the e- in the outer shell

19. Carbon forms covalent bonds H DNA N S C caffeine C N amino acid- phenylalanine O graphene Source: http://news.discovery.com

20. Metallic bonds • Positive ions surrounded by unrestricted electrons • These can flow through the medium, which explains why metals are good conductors of electricity • Can bond atoms of a single element or form alloys of two or more metals. • Common metallic bonding elements are: Au, Ag, Ni, Cu, Zn, Pt.

21. Xe atom on Ni crystal face • STM – Scanning Tunneling Microscope is used to image the atomic structure of solids • Xenon = blue circle • Nickel = red dots • Note vacancies in the structure (black holes) http://www.almaden.ibm.com/vis/stm/gallery.html

22. Let’s try it • It’s time for some bonding! • You are an element. Take a card from the center of your table. • To what group of elements do you belong? Are you likely to bond in ionic, covalent, or metallic bonds? • You may have more than one option, or you may not bond at all. • Now find someone to bond with. Think about what your charges are if you become an ion.