Katy Johanesen
Ph.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!
Questions? Email johanese@usc.edu
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
Outermost shell =
valence electrons
• Energy is absorbed when an e- moves out a level, and
emitted when it moves in.
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
H
DNA
N
S
C
caffeine
C
amino acidphenylalanine
N
O
graphene
Source: http://news.discovery.com
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.