ch.8 - 11/2/2009 We!have!learned!a!lot! about!the!atoms in!

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
11/2/2009 1 We have learned a lot about the atoms in penicillin and the structure of atoms. We have learned about a few common chemical reactions and about energy and enthalpy for reactions. http://www.udel.edu/chem/white/C647/Penicillin.gif Penicillin Now we need to learn about the bonds between atoms! • Metallic – framework of positively charged cations Types of Chemical Bonding surrounded (and held together) by a sea of (valence) electrons. • Ionic – attraction between positively charged cations and negatively charged anions. • Covalent Bonding – when electrons are shared between (typically) 2 atoms.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
11/2/2009 2 IONIC vs. MOLECULAR Ions in salts held together by IONIC interactions formed by electron transfer Atoms in molecules held together by COVALENT bonds formed by electron sharing Molecular Structure A full description of the structure of a molecule and the chemical bonds in it requires the solution of the Schrödinger equation for the entire molecule. !" #$ % & E r V T E H ( ) ( , , ˆ ˆ ˆ The potential term is far too complicated to be solved analytically and so we need an empirical approach to molecular structure. ! " , , ˆ r V
Background image of page 2
11/2/2009 3 Molecular Structure There are two common approaches - Lewis description - V alence S hell E lectron P air R epulsion (VSEPR) theory (Chapter 9) and both are based on the electron count at the central atom of the molecule or fragment of the molecule. Molecular Structure Lewis description The covalent chemical bond can be thought of as a pair of be thought of as a pair of electrons shared between atoms. By considering the number of electrons in the valence shell and the G. N. Lewis number of electrons in the outer atoms, we can explain the presence of lone pairs and the gross structure of the molecule in simple cases.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
11/2/2009 4 Molecular Structure Lewis description The Lewis description arose form an attempt to cram the observed an attempt to cram the observed properties of atoms in combination into a mechanically classical picture of the physical world then prevalent; in fact even G. N. Lewis classically, the structure of the atom was not explicable. http://www.chem.yale.edu/~chem125/125/history99/7BondTheory/LewisOctet/ cubicoctet.html Molecular Structure Lewis description The Lewis description is based on the observed requirement that the atom achieves the valence shell requirement that the atom achieves the valence shell octet associated with the noble gases - a noble gas configuration. Consider the formation of MgCl 2 Mg: 1 s 2 2 s 2 2 p 6 3 s 2 or [Ne]3 s 2 Cl: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 5 or [Ne]3 s 2 3 p 5
Background image of page 4
11/2/2009 5 Molecular Structure Lewis description We know that MgCl 2 is ionic and so the changes in the valence shell configurations are the valence shell configurations are Mg: 1 s 2 2 s 2 2 p 6 3 s 2 or [Ne]3 s 2 Mg 2+ :1 s 2 2 s 2 2 p 6 or [Ne] Cl: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 5 or [Ne]3 s 2 3 p 5 Cl - : 1s 2 2s 2 2p 6 3s 2 3p 6 or [Ne]3s 2 3p 6 (i.e. [Ar]) Molecular Structure Lewis description We therefore account for the stability of MgCl 2
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 05/11/2010 for the course CHEM 1201 taught by Professor Cook during the Spring '08 term at LSU.

Page1 / 36

ch.8 - 11/2/2009 We!have!learned!a!lot! about!the!atoms in!

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online