CH131_3A

CH131_3A - Homework Assignment #3 Read 3.1 - 3.9 Problems...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
Homework Assignment #3 Read 3.1 - 3.9 Problems Chap 3 - 9, 15, 21, 23, 33, 39, 41, 43, 45, 47, 51, 53, 55, 57, 59, 61, 65, 69
Background image of page 1

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

View Full DocumentRight Arrow Icon
Chemical Bonding: forces that bind atoms together When 2 atoms approach each other, the electrons can rearrange their spatial distributions so that “chemical bond” are formed. i.e. new spatial arrangement lowers potential energy - more stable- than when atoms are far apart- and chemical bonds (atoms stick together) are formed. Questions to answer : 1. Why bonds form between certain elements and not others? For example: NaCl not NaHe stable molecule 2. What determines ratios of elements in stable molecules? H 2 O not H 4 O? 3. What determines the shapes of molecules? H 2 O is bent O
Background image of page 2
The key observation at the beginning of the 20th century that led to the theory of chem. bonding => discovery of inert gases (Gr. VIII elements) => did not form chemical bonds w/ other elements or themselves! Noble (inert) gases had electronic configurations of great stability and hence chemical inert. i.e. electron configuration of inert gases had most stable configuration. Group VIII => have 8 valence e - (special) Based on this inert gas stability, G. N. Lewis proposed a theory of chemical bonding.
Background image of page 3

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

View Full DocumentRight Arrow Icon
General ideas of Lewis theory: 1. Electrons found in shells => valence e - are the electrons in the outermost shells (same as Group # main group elements) inner shell e - => core electrons properties of chemical bonding are due to valence e - ’s. Hence, most chemical properties due to valence e - ’s. 2. Some chemical bonds called ionic bonds => result from complete transfer of e - from one atom to another. 3. (at other extreme) some chemical bonds due to sharing of valence e - ’s => covalent bonds . 1. (most in between => polar covalent bonds ). In either case, guiding principle to chemical bonding is Octet Rule: atoms try to surround themselves (by losing, gaining or sharing) with 8 valence e - ’s when forming molecular species
Background image of page 4
Octet rule => a general tendency => many exceptions => But most representative elements try to achieve Noble/Inert gas/Group VIII valence configuration Desire to achieve “octet” configuration drives chemical bonding characteristics!
Background image of page 5

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

View Full DocumentRight Arrow Icon
energy IP 1 (IE 1) X(g) X(g) + Some quantitative concepts for understanding chemical bonding (i.e. electron rearrangement/gain/loss) Ionization energy (IE) => minimum energy required to remove e from a species (usually in the gas phase). => measure of an atom’s relative ability to lose an e - X ( g ) hn X + ( g ) + e _ h ν = light X + positively charged ion (cation) define: E => a change in energy=> E = E(products, RHS) – E(reactants, LHS) = IP 1 (IE 1 ) IP 1 (IE 1 ) = first ionization potential (energy) E, IP 1 > 0 energy must be supplied - as shown in energy level diagram on left.
Background image of page 6
Subsequent e - ’s could be removed i.e. second ionization potential X + ( g ) hn X +2 ( g ) + e _ IP 2 (IE 2 ) IP 2 > IP 1 IP 1 increases going from Gr I Gr VII for a given period; Easier to remove an e - from Gr I than Gr VII Elements in lower group #’s more easily give up e - ’s IP => measure of relative ability to lose an e - .
Background image of page 7

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

View Full DocumentRight Arrow Icon
Electron affinity (EA) => measure of energy released when e - becomes attached to a neutral atom
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/17/2008 for the course CAS CH131 taught by Professor Zigler during the Spring '08 term at BU.

Page1 / 27

CH131_3A - Homework Assignment #3 Read 3.1 - 3.9 Problems...

This preview shows document pages 1 - 9. Sign up to view the full document.

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