Chemical Bond
Lattice Energies and Types of Ions
Na (s) + 1/2Cl2 (g)  NaCl (s) ΔH= -411 kJ/mol
Energetically favored: lower energy
Like a car rolling down a hill
We will not be doing these type of calculations however, if interested then can read on
your own
Question why Cl- and not Cl2Na+ and not Na2+
Mg2+ and not Mg+
Answer energetically most favored always have cation and anion
Get out more energy than you put in
Born Haber cycle is formal method of keeping track of energy changes
Periodic Table (older Roman numerals)
IA
IIA
IIIA s2 and s2p6 ions
VA
VIA VIIA s2 and s2p6 ions
IB
IIB
d10 ions
IIIA IVA VA
d10s2 ions
Transition metals frequently form more than one type of cation
Most will form +2 by losing 4s2 electrons and some others are more complex structures
Example:
Pour ammonia solution in bottle and add concentrated HCl to produce a white smoke
NH4Cl which stays in bottle. Add water and shake and white smoke disappears because
NH4Cl is soluble in water
NH3 + HCl  NH4+Cl- (ammonium chloride)
Bonding General Concepts
Chemical Bonds – atoms combine, Electron distribution changes
Types of Bonds: Ionic, Covalent and Metallic
Ionic Bonds is the transfer of electrons (ex. salts, crystals) and is composed of a positive
(cation) and negative (anion)
Covalent is the sharing of electrons and the compound is either molecular (CH4) or
networking (diamond)
Metallic Bond is the outer electrons move throughout solid and holds nuclei together and
the compound is only composed of metals
Conduction of Electricity
Type of Bond
Compound
Ionic
Solid NaCl
Conduct
Electricity
No
Ionic
Covalent
(molecules)
Covalent
Liquid NaCl
Solid Cl2
Yes
No
Liquid Cl2
No
Metallic
Solid Na
Yes
Metallic
Liquid Na
Yes
Explanation
Na+Cl- ions held
rigid
Ions free to move
Cl—Cl all electrons
tied up
Cl—Cl all electrons
tied up
Outer electrons
move throughout
metal
Electrons free to
move throughout
More unpaired than would expect from electron configuration because of hybrid orbitals
Valence Electrons
By sharing or transferring valence electrons the electronic configuration of noble gases
frequently obtained from A family elements
Element
He
Ne
Ar
Kr
Xe
Metal
and
Electrons Lost
Na
[Ne] 1s1
Inner electrons
(He)
(Ne)
(Ar)3d10
(Kr)4d10
Nonmetal
Electrons Gained
Cl
[Ne] 3s23p5
Octet Rule
Rules of Eight and Two works for IA, IIA, Nonmetals
H, Li, Be
H-, Li+, Be2+ Isoelectronic with the same electronic structure
Eight (Octet Rule) Na+, F-1, O-2
Isoelectronic with (Ne)
Exceptions especially in d orbital
Lose electrons in different order than build up
Transition element loses electron from outer s subshell first
Zn [Ar] 3d104s2  Zn2+ [Ar] 3d10 + 2ePseudonoble gas configuration ns2np6nd10
Ionic Bond
Electron dot structure
Sodium metal explosive metal when added to water
Chlorine gas is a poisonous gas
Sodium chloride white crystal essential for life transfer e-
Outer electrons
1s2
2s22p6
3s23p6
4s24p6
5s25p6
Bonds:
Ionic
(http://www.chemistry.montana.edu/bchm204/pages/elements_files/elements.html)
Covalent
Cl + Cl  Cl2
The Cl—Cl bond shares electrons to complete the octet
Element
Valence e-
s
p
p
p
Al
3s23p1
__ __ __ __
Na
3s1
__ __ __ __
O
2s22p4
__ __ __ __
Cl
3s23p5
__ __ __ __
Show valence electrons
The valence electrons are the ones beyond the noble gas or beyond noble gas and d
electrons
(The number at the top of the periodic table)
Water H2O
(http://www.olemiss.edu/courses/chem105_jg/CHEM%20105-Ch%209/CHEM%20105-Ch%209.html)
(http://www.owlnet.rice.edu/~chem122/class/assignments/SBR_Homework/Homework7.htm)
Lewis Structure is a powerful technique to predict the structure of water
In transfer the electrons lost must be equal to electrons gained
Mg
+
(cation)
F+F 
Mg2+
+
2F-
(anion)
= lost 2
+
2(gain 1)
Ionic Compound
All halogens form diatomic molecules (single bond)
F—F
Cl—Cl
Br—Br
I—I
What about N2 and O2?
Lewis dot structures of valence bond structures
Number of valence electrons + group number for nonmetals
Group
14 (4A or IV)
15 (5A or V)
16 (6A or VI)
17 (7A or VII)
18 (8A)
Example
C, Si
N, P
O, S
F, Cl, Br, I
# of Bonds
4
3
2
1
0 (normally)
Once a particular element in the table bonds to their respective number then they have a
noble gas like structure
Notice the number of bonds directly correlates to how far they are from the noble gas on
the periodic table
(http://www.chemistry.ohiostate.edu/~grandinetti/teaching/Chem121/lectures/chemical%20bonds/bonds.html)
4 nonbonding electrons and 6 bonding electrons
(http://www.chemistry.ohiostate.edu/~grandinetti/teaching/Chem121/lectures/chemical%20bonds/bonds.html)
8 nonbonding electrons and 4 bonding electrons
Bonds = (electrons need – electrons have)/2
Electrons Need refers to the rule of eight and rule of two
Electrons Have refer to valence electrons
N2 (16-10)/2 = 3
O2 (16-12)/2 = 2
HF (10-8)/2 = 1
Covalent Bond and Lewis Structures
Share electrons – a pair of electrons ~ 1 bond
H2 simplest molecule
(http://mws.mcallen.isd.tenet.edu/mchi/ipc/ch07htm/ch07sec3.htm)
Positive nuclei are attracted toward each other by negative charge in between them
Each Hydrogen atom satisfied the noble gas structure
Think of 2 electrons being around each Hydrogen
1s2 structure for each
H2 discrete unit
NaCl ionic compound, simplest ratio, not separate entity or species
F [He] 2s22p5
(http://www.hull.ac.uk/php/chsajb/concepts/ho_2.html)
Each F 2s22p6
12 nonbonding electrons
2 bonding electrons
Family A elements (not transition elements) satisfy rule of 8 or rule of 2 (H)
Covalent
Examples of Covalent Bonds:
(http://dl.clackamas.cc.or.us/ch104-07/bonding1.htm)
(http://www.up.ac.za/academic/chem/mol_geom/bent2.htm)
(http://www.ausetute.com.au/lewisstr.html)
(http://chemsite.lsrhs.net/d_bonding/lewis_dots.html)
Lewis Structural Formula 1916
Unshared electrons are referred to as lone pairs
(http://scidiv.bcc.ctc.edu/wv/5)
Whenever possible the Rule of Eight is followed
Exceptions to Rule of Eight (Octet Rule)
Examples:
Boron trifluoride
(http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch8/lewis.html)
Phosphorus pentachloride
(http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/09.html)
Multiple Bonds
Single Bonds
Double Bonds
Triple Bonds
All can be used to satisfy the Rule of Eight
Ethane, Ethene, Ethyne
(http://www.sciencecollege.co.uk/SC/atomic_molecular_structure.html)
Ethane
(http://scidiv.bcc.ctc.edu/wv/5)
Bonds = (need – have)/2
((12 + 8 + 8) – (6 + 4 + 4))/2
(28-14)/2 = 14/2 = 7
(http://www.moorlandschool.co.uk/earth/alkanes.htm)
Ethene
(http://www.wpbschoolhouse.btinternet.co.uk/page06/molecule_shapes.htm)
Bonds = (need – have)/2
((8 + 8 + 8) – (4 + 4 + 4))/2
(24-12)/2 = 12/2 = 6
Chemist use lines when drawing Lewis structures
One line equals two electrons shared between two atoms
and these two electrons compose one bond
Ethyne (Acetylene)
(http://www.cartage.org.lb/en/themes/Sciences/Chemistry/Inorganicchemistry/Informationbonding/bonding
index/multiplebonds/multiplebonds.htm)
Bonds = (need – have)/2
((4 + 8 + 8) – (2 + 4 + 4))/2
(20 – 10)/2 = 10/2 = 5
Resonance Hybrid
Lewis Structure for SO2 (sulfur dioxide)
(http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch8/lewis.html)
These are resonance forms with equivalent structures just the bonds are in different
places
This molecule is a resonance hybrid
Really doesn’t mean that the structure flips back and forth rather there is a hybrid
(intermediate) that includes both of theses structures
The hybrid has two 1 ½ bonds in which 2 e- are spread between 3 atoms
Bonds = (need – have)/2
(24 – 18)/2 = 6/2 = 3 bonds
Normal Lewis Structures don’t always work
Limitation of the theory
We can have fractional bond order
Lewis Structure for N2H4 (hydrazine)
(http://www.answers.com/topic/hydrazine)
Bonds = (need – have)/2
((8 + 8 + 2 + 2 +2 +2) – ( 5+ 5 +1 + 1 + 1 + 1))/2
(24 – 14)/2 = 10/2 = 5 bonds
Coordinate Covalent Bond both electrons donated by one atom
Lewis Structure of HNO2 (hydrogen nitrite)
O=N—N—H
To form HNO3 (hydrogen nitrate) in solution with nitric acid
(http://www.elmhurst.edu/~chm/onlcourse/chm110/outlines/topic8.html)
Bonds = (need –have)/2
(34-24)/2 = 10/2 = 5 bonds
Formal Charge = + (group #) – ( # of bonds + # unshared electrons)
+5 – (4) = +1 for N
+6 – (7) = -1 for O with single bond
+6 – (6) = 0 for O with double bond
In solution break the O—H bond
(http://www.mpcfaculty.net/mark_bishop/resonance.htm)
(Note: negative adds an electron and positive removes an electron)
Bonds = (need – have)/2
(32 – 24)/2 = 8/2 = 4 bonds
Formal Approach to Drawing Lewis Structures
1. Total number of valence electrons
positive ion decrease by charge
negative ion increase by charge
2. Number of needed electrons to give each atom 8 e- and each Hydrogen 2 e3. Number of bonding e- + ( needed e-) – (valence e-)
4. Bonds = Bonding e-/ 2
5. Indicate position of atoms
6. Draw dash for each bond
7. Complete octet (other than H) for each atom filling in unshared e# unshared e- = (total e-) – ( # bonding e-)
Formal charge = +(group valence #) – ( # bonds + # unshared electrons)
Formal charge is a way of saying if an atom has fewer or more electrons than it
needs to satisfy octet rule. In N2 below each N has 0 (zero) formal charge
because each has 5 valence electrons to start with and ( 3 bonds + 2 electrons in
lone pair= 5 ) so 5 – 5 = 0 zero formal charge
Example:
N2
1. Valence given = 10
2. Needed + 16 ( 2 x8)
3. need 6 bonding electrons
4. or 3 bonds (6/2)
5. so N2 has triple bond
6.
(http://www.chemistry.ohiostate.edu/~grandinetti/teaching/Chem121/lectures/chemical%20bonds/bonds.html)
7.
(http://members.optushome.com.au/scottsoftc/chapter04/section4.html)
# unshared e- = (total e-) – ( # bonding e-)
10 – 6 = 4 unshared eMeasure of Charge Separation in Molecules (dipole moment)
Dipole moment = (charge)(distance)
HCl observed dipole moment
Polar molecules affect charge that pair of electrically charged plates can hold
(http://www.800mainstreet.com/5'/0005-0009-lining.gif)
HCl = 1.03 D debye (Coloumb)(m) ~ 3.34 x 10-30 C x m
If charge completely transferred
= (1.60 x 10-19 C)( 1.27 x 10-10 m )(D/3.34 x 10-30 C x m)
= 6.08 D
Observed/ predicted by transfer = 1.03/6.08 = 17% ionic
Left (metal) with right (nonmetal) is a ionic bond
Nonmetal with Nonmetal is polar covalent
Nonmetal with Nonmetal can also be pure covalent
NaCl ionic
MgCl2 ionic
PCl3 covalent