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Katy JohanesenPh.D. Candidate, USC Department of
Earth Sciences
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!
• 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 [email protected]
Today’s lecture has two parts
Atoms Molecules and Compounds
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
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
Emission Spectroscopy
• Each element emits different wavelengths of light (energy) when
• Niels Bohr explained this with a new model of the atom!
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
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)
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
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.
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.
Na (Sodium) and Cl (Chlorine)
Na (Sodium) and Cl (Chlorine)-+
NaCl (table salt) crystals
Source: http://www.sciencephoto.com
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.
O (Oxygen): atomic number 8
O2
Note: only two electrons from each atom are shared, not all the e- in the outer shell
Carbon forms covalent bonds
Source: http://news.discovery.com
caffeine
amino acid-phenylalanine
graphene
DNA
CN
H
S
C
NO
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.
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
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.