O-Chem

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C H EM 301A - O rganic Chem istry L ecture N otes

© Dr. Peter de Lijser, 2011

Introduction – Welcome to O-chem!
“What is Organic Chemistry?”
Organic chemistry is the chemistry of Carbon.
“Why is Organic Chemistry Important for me?”
Organic Chemistry is the central science for many other fields: •

Medicine/Pharmacy:



Biochemistry:



Industrial Applications:



Reaction Mechanisms:

What do "Organic Chemists" do?


Discover new reactions



Improve old reactions



Make new compounds



Isolate natural products



Study reaction mechanisms

Most importantly, studying Organic Chemistry will teach how to think in an “analytical” manner about problems and it will teach you problem solving skills. No matter what you will end up doing in your life, you will at some point need problem solving skills. No doubt, there will come a time when you are faced with a problem that will look unfamiliar to you, but with your basic knowledge you can deal with the situation and come up with a solution. Being able to apply your knowledge to an unknown problem is a tremendously important and beneficial skill!

C H EM 301A - O rganic Chem istry L ecture N otes

© Dr. Peter de Lijser, 2011

T opic A 1 : S tructure and Bonding
The Periodic Table

The nucleus contains positively charged protons and uncharged neutrons. The electron cloud is composed of negatively charged electrons.

Elements in the same row are similar in size.
Elements in the same column have similar electronic and chemical properties.

An s orbital has a sphere of electron density and is lower in energy than the other orbitals of the same shell. A p orbital has a dumbbell shape and contains a node of electron density at the nucleus. It is higher in energy than an s orbital.

C H EM 301A - O rganic Chem istry L ecture N otes

© Dr. Peter de Lijser, 2011

Since there is only one orbital in the first shell, and each shell can hold a maximum of two electrons, there are two elements in the first row, H and He.

Each element in the second row of the periodic table has four orbitals available to accept additional electrons: one 2s orbital, and three 2p orbitals.

Second Row Elements
Since each of the four orbitals available in the second shell can hold two electrons, there is a maximum capacity of eight electrons for elements in the second row. The second row of the periodic chart consists of eight elements, obtained by adding electrons to the 2s and three 2p orbitals.

C H EM 301A - O rganic Chem istry L ecture N otes

© Dr. Peter de Lijser, 2011

Review of Bonding
Bonding is the joining of two atoms in a stable arrangement. Through bonding, atoms attain a complete outer shell of valence electrons (noble gas configuration.) Ionic bonds result from the transfer of electrons from one element to another. Covalent bonds result from the sharing of electrons between two nuclei. An ionic bond generally occurs when elements on the far left side of the periodic table combine with elements on the far right side, ignoring noble gases.

A positively charged cation formed from the element on the left side attracts a negatively charged anion formed from the element on the right side. An example is sodium chloride, NaCl.

Bonding in Molecular Hydrogen (H2)
Hydrogen forms one covalent bond.
When two hydrogen atoms are joined in a bond, each has a filled valence shell of two electrons.

Second row elements can have no more than eight electrons around them. For neutral molecules, this has two consequences: • Atoms with one, two, or three valence electrons form one, two, or three bonds, respectively, in neutral molecules. • Atoms with four or more valence electrons form enough bonds to give an octet. This results in the following equation:



When second-row elements form fewer than four bonds their octets consist of both bonding (shared) and nonbonding (unshared) electrons. Unshared electrons are also...
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