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 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

• 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.