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Chemical Bonding Ch78

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Electrons in the highest occupied energy level of an element's atom ... Trigonal Planar. Trigonal Pyramidal. Tetrahedral. Trigonal Bipyramidal. Octahedral ... – PowerPoint PPT presentation

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Title: Chemical Bonding Ch78

1
Chemical Bonding Ch7-8

Chemistry
Mr. Perkins

2
Valence Electrons

Electrons in the highest occupied energy level of
an elements atom
Determines chemical properties
Used in formation of chemical bonds
For Representative Elements (group A) number
can be matched to group number
Electron Dot Structures shows valence electrons
as dots
http//darkwing.uoregon.edu/ch111/L12.htm

3
Octet Rule

Atoms will react to achieve a full octet 8
electrons in the outer energy level
Atoms will either lose or gain electrons (form
ions), or share electrons to become more stable

4
Ionic Bonds (Ch 7)

Cation positive ions
Anion negative ions
Electrostatic attraction between opposite charges
Ionic Bond
Chemical bond formed by electrostatic attraction
Compounds known as salts

5
Properties of Ionic Compounds

Electrolytes
Crystal lattices / crystalline structure
Brittle solids
High melting and boiling points
Coordination number
of oppositely charged ions next to each ion
NaCl Coordination number 6

6
Why do atoms form ions?

To achieve lowest possible energy
To achieve stable electron configurations
To achieve same configuration as a noble gas

7
Stable Electron Configurations for Cations

Sodiums Configuration
Sodium Ion Configuration
Neons Configuration
Some ions are exceptions to the octet rule

8
Stable Configurations for Anions

Chlorine atom
Chloride ion
Argons configuration

9
Ionic Compound Formation

Sodium Chloride
Aluminum Bromide
Smallest particle in an ionic compound is called
a formula unit not a molecule
Formula unit charge must be zero
All compounds are electrically neutral
Ionic Compounds generally a metal and nonmetal
Called Salts

10
Metallic Bonds

Free floating sea of valence electrons surround
positively charged metal cations
Properties of metals
Good conductors of heat electricity
Malleable
Ductile
Among the simplest crystalline solids

11
Alloys

Metals melted together/solid solutions
Interstitial alloys in-between layers
Substitutional alloys atoms of one metal
replace atoms of another metal in crystalline
structure
Dental amalgams alloys of Hg, Ag, Zn
Sterling Silver Ag, Cu
Stainless Steel Fe, C, Cr, Ni

12
Covalent Bonding (Ch 8)

Sharing of electrons
H2 is the simplest molecule
Molecular formulas show the number and kind of
atoms present in a molecule
7 diatomic molecules
N2, O2, F2, Cl2, Br2, I2, H2

13
Lewis Structures for Compounds

http//www2.gasou.edu/chemdept/general/molecule/le
wis.htm

14
Covalent Bonding Cont.

Double Bonds
Two pairs of electrons are shared
H2CCH2
http//darkwing.uoregon.edu/ch111/L13.htm

Triple Bonds
Three Pairs of electrons are shared
Coordinate Covalent Bond when 1 atom
contributes both shared electrons
Ex Carbon monoxide
Ex Ammonium Ion
Most Polyatomic ions have coordinate covalent
bonds

15
Resonance Structures

Occurs when 2 or more equally valid electron dot
structures can be written for a molecule
Put resonance structures in brackets
Show resonance with a double pointed arrow
Examples ozone, O3 benzene C6H6
All bonds are actually of identical strength,
stronger than single, and weaker than double
You Try It!! Draw structures for CO32- (Carbonate
Ion)
http//www2.gasou.edu/chemdept/general/molecule/re
sonan.htm

16
Exceptions to the Octet Rule

Some larger atoms may hold more than the
predicted 8 valence electrons because of bonding
d orbitals.
XeF4
PCl5
SF6

17
Molecular Orbitals

Sigma bonds are formed when two atomic orbitals
combine to form a molecular orbital that is
symmetrical around the axis connecting the two
nuclei
Pi bonds form when there is side by side overlap
of atomic p orbitals this is not symmetrical
around the bond axis
Sigma bonds are stronger due to better overlap of
atomic orbitals

18
VSEPR Theory

Valence Shell Electron Pairs orient themselves so
that the Repulsions between them are minimized
Linear
Bent
Trigonal Planar
Trigonal Pyramidal
Tetrahedral
Trigonal Bipyramidal
Octahedral
http//www.molecules.org/VSEPR_table.html

19
Hybrid Orbitals

Hybridization occurs when several atomic orbitals
mix to form the same total number of equivalent
hybrid orbitals
4 single bonds sp3 hybridization
2 single, 1 double sp2 hybridization
A sigma and pi bond form the double bond
1 single, 1 triple sp hybridization
A sigma and 2 pi bonds form the triple bond

20
Polar Bonds

Dipole two separated, but equal and opposite
charges
Some molecules are slightly positive at one end
and slightly at the other end
Electronegativity Values The measure of the
attraction for a shared pair of electrons
assigned by Linus Pauling
Difference between values predicts the type of
bond 0-0.4 nonpolar 0.4-2.0 polar 2.0 -
ionic
HF H2.1 F4.0 Difference 1.9 very polar
covalent
Three types of bonding do not reflect different
mechanisms, rather a way to classify the degree
of sharing electrons that occurs in any bond.
http//www2.gasou.edu/chemdept/general/molecule/po
lar.htm

21
Intermolecular Forces - VanderWaals Forces

London Dispersion Forces The greater the number
of electrons, the greater the motion the
stronger the attraction between molecules
FltClltBrltI
Dipole-Dipole Polar mc attracted to each other
Hydrogen Bonding hydrogen of one mc is
attracted to more electronegative atom of another
mc.
Shapes of molecules affects interactions
http//www2.gasou.edu/chemdept/general/molecule/fo
rces.htm

22
Lab Quiz