Chemical Bonding What holds things together?

Chemical BondingWhat holds things together? PGCC CHM 101 Sinex

Conductivity - high Conductivity - low Let’s examine the melting point of compounds across two periods. What is the trend? high low CRC Handbook of Chemistry and Physics, 1995

Bonding Can we explain the melting point behavior across a period? • involves the valence electrons or outermost shell (or highest shell) electrons • the group number tells how many valence electrons (if there is two digits eg 15, only look at the last one ie 5) How many valence electrons on N? Group 15 – 5 valence electrons

F F Bonding… • Lewis dot structures show the valence electrons around at atom and for most molecules and compounds a complete octet for the elements • most monatomic ions have an electron configuration of noble gases Al N 2 .2 .5 + e- 2 .2 .6 Ne

Write out the electron configuration for the following atoms and ions: He Ne Ar Kr H- Ca+2 O-2 Br- Which noble gas is isoelectronic with each ion?

Cl Cl NaCl This is the formation of an ionic bond. - + Na Cl electron transfer and the formation of ions Cl2 This is the formation of a covalent bond. sharing of a pair of electrons and the formation of molecules

Draw the Lewis dot structures for the following compounds: ionic MgO CaCl2 Na2S covalent HCl H2O CH4

Some exceptions to the Octet Rule BF3 PCl5 SF6

Electronegativity The electronegativity difference - DEN = ENhigher – EN lower large difference small difference

Using electronegativities to determine bond type DEN > 1.7 ionic bond - transfer DEN < 1.7 covalent bond - sharing So we have a range of electronegativity difference of 0 to 1.7 for sharing an electron pair.

X Y DEN = 0 X Y DEN = 0.3 X Y DEN = 0.6 increasing polarity of bond X Y DEN = 0.9 polar bond 0 < EN< 1.7 X Y DEN = 1.2 Is the sharing of electrons in molecules always equal? non-polar bond Which element is more electronegative? ENY > ENX Direction of electron migration

Space-filled BF3 – a planar molecule F 4.0 B 2.0 Ball & stick negative top side positive Electrostatic potential maps Spartan ‘02

O O O O O O double bond (2 pairs) N N N N N N N N triple bond (3 pairs) More sharing examples O2 Share until octet is complete. N2 octet complete

normal covalent bond (each atom supplies an electron) coordinate covalentbond (the pair of electrons from the same atom) H H H H H H Some more sharing examples NH3 N NH4+ NH3 + H+ NH4+ H+ N

Type of bond? – I, PC, or NC TiO2 CH4 NaI CS2 CO2 KCl AlCl3 CsF HBr

Using the EN trends to predict bond type Increasing EN Increasing EN 105 Db 107 Bh NO RbF FeS H2S Modified from http://www.cem.msu.edu/~djm/cem384/ptable.html

Draw the Lewis dot structures CO2 NH2- H3O+ CO HCN H2CO (C in center)

Show the direction of electron migration ( ) in the following. C – H H – F C = O C – Cl Rank the bond polarity (1-most … 3-least) As-H N-H P-H

Here is the electrostatic potential map for H2CO. Show the electron migration on this planar molecule. H C O H blue – positivered - negative How is this molecule different than BF3?

Comparison of Bonding Types ionic covalent ions molecules molten salts conductive non- conductive valence electrons transfer of electrons sharing of electrons high mp low mp DEN > 1.7 DEN < 1.7

A B A+ B- A B Increasing DEN Increasing polarity 100% covalent 100% ionic Bonding spectrum Transfer

Chemical Bonding What holds things together?