Transcript Atomic Structure, Molecular Structure & Bonding

Introduction
&
Atomic Structure, Molecular
Structure and Bonding
Organic Chemistry: Introduction
What Is Chemistry?
Chemistry Is The Study Of Matter & The Changes It Undergoes
Two Main “Branches” of Chemistry
Organic
Chemistry
Inorganic
Chemistry
• Term Coined by Berzelius ~ 1807
• Matter Derived From Nonliving Things
• Matter Derived From Living Things
• Vast Majority of the Periodic Table
• Study of Carbon Compounds (C,H,N,O)
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Influence of Organic Chemistry
Organic Chemistry Is Important to Medicine: Ancient and Modern
• Plant Extracts as Medicines…Active Ingredients are Organic Compounds
• Prescription Drugs….Prepared by “Synthetic Chemists”
Organic Chemistry and Dyes:
• 1st Solid Link of Industry and Research
• $$ Derived From Research
Organic Chemistry and Materials Development:
• Synthetic Fibers….Nylon
• Synthetic Rubber….Neoprene
• Chemistry of Polymers (Plastics)
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Organic Chemistry and You?
Redox Reactions
Alcohols
Aldehydes
Ketones
Alkanes/alkenes
Ethers
Carboxylic acids
Concentration
Redox Reactions
Spectrometry
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In this unit, we will review…
1.
2.
3.
4.
5.
6.
Atomic Structure
Lewis Dot Structures and Formal Charge
Ionic and Covalent Bonds
Electronegativity and Polarity
Molecular Geometry
Multiple Bonds
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Modern Atomic Theory
Atoms have an internal structure consisting of one or
more subatomic particles:
proton  positive charge
mass = 1.673 x 10-27 kg
neutron  no charge
mass = 1.675 x 10-27 kg
electron  negative charge
mass = 9.109 x 10-31 kg
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Most of the mass of an atom is concentrated in the
nucleus, which contains one or more positively
charged protons and neutrons with no electrical
charge.
proton
neutron
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One or more negatively
charged electrons are in
constant motion outside
the nucleus.
What is the overall
electrical charge if the
number of electrons
equals the number of
protons?
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Valence and Core Electrons
Electrons contained in the outermost shell are called
________electrons.
All other electrons are called ______ electrons.
e-
ee-
ee-
How many valence electrons does this
atom have? Core electrons? Which
number matters more?
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1
How many valence electrons (ve-’s) does
carbon have? Calcium? What element is
depicted in the image on the right?
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Chemical Bonding
Chemical bonds are the forces that hold atoms
together in compounds. We use Lewis Dot
structures to represent these atoms and
compounds.
C
O
C
O
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Drawing Lewis Dot Structures
1. Count total ve-’s available
2. Draw a Lewis sketch
– H is never central; C is often central
3. Draw in electrons to fulfill octet and duet rules
– C “likes” 8 electrons; H “likes” 2 electrons
4. Count ve-’s and compare to #2
5. If too many e-’s, make a double bond
6. Calculate formal charge (FC) to double check structure
– No or low FCs (e.g. +1) more likely than large FCs (e.g.
+2)
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Example
NH3
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Formal Charge
Formal charge = ve-’s – (lone pairs + bonds)
In a neutral molecule, the sum of the FCs = zero. For an
ion, the sum of the FCs = the charge of the ion.
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Formal Charge –the easy way!
1. Circle the atom of interest.
2. Count the electrons inside the circle. If the circle
“breaks” a bond, only count one electron of the bond.
3. Take the ve-’s for the atom (its group number) and
subtract #2.
FC of oxygen= 6 – (6) = 0
O
C
O
FC of carbon= 4 – (4) = 0
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Resonance Structures
Resonance structures result when more than
one valid Lewis dot structure can be drawn for
one molecule.
– The positions of the nuclei can’t change (C, H, etc.)
– The positions of multiple bonds or lone pairs can
move
– Low FCs are still favored
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Computing Formal Charges
“Normal” covalent bonding patterns:
Carbon
Nitrogen
Oxygen
C
N
O
C
C
C
N
N
O
Halogens
X
Onebond
Threelonepairs
Twobonds
Twolonepairs
Threebonds
Onelonepair
Four bonds
Nolonepairs
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Formal
Charges
Common Computing
structures with
formal
charges:
C
a
rb
o
n
C
N
itro
g
e
n
O
x
y
g
e
n
O
N
H
a
lo
g
e
n
s
X
N
C
O
N
N
N
O
N
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Ionic versus Covalent
Bonds formed by the transfer of electrons from one atom to
another are __________.
Example:
Sodium chloride (NaCl)
Na
 Na+ + eCl + e-  Cl- __
Na + Cl  NaCl
+
+
+
_
_
+
+
+
_
_
+
+
+
_
_
+
+
+
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Bonds formed by the sharing of electrons between two atoms
are __________.
Example:
Glucose (C6H12O6)
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Polar Covalent Bonds
Polar bonds are bonds between atoms created
by sharing electrons unevenly.
H F


F F
Uneven sharing is the result of electron “greedy”
atoms (i.e. more electronegative atoms).
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Electronegativity
Electronegativity is a measure of the tendency of an
atom to attract a bonding pair of electrons.
Electronegativity differences result in polar covalent bonds.22
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Polar Covalent Molecules
A polar molecule is a molecule that is electrically
asymmetrical, resulting in charges at two points. The
molecule is said to have a molecular dipole or dipole
moment.
HC
l
O
H H
O
C
H
C C
H
3
3
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Polar Covalent Molecules
Not all molecules that contain polar bonds will
be polar molecules!
OCO
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Molecular Geometry
Common geometries:
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PQ
Acetone
C3H6O
Is acetone ionic or covalent?
What its geometry?
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 Atomic orbitals (AOs)are the probability distribution
about one atomic nucleus(found using wave functions ψ)
 AOs relate to quantum numbers (n, l, ml, ms)
 Each AO can have, at most, two e- (Pauli Exclusion Principle)
 AOs are filled with e-’s from the lowest energy to the
highest (Aufbau Principle)
 The electron configuration with the highest number of
unpaired spin is more stable (Hund’s rule)
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Atom
Electronic
Structure
Electronic
Configuration
LewisDot
Structure
3p
3s
Boron
2
2
1
1s 2s 2p
2p
2s
B
1s
3p
3s
Phosphorus
2
3
[Ne] 3s 3p
2p
2s
P
1s
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Scandium
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Carbon
AtomicNumber
Number==66
Atomic
2p
2s
1s
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Hybridized Orbitals
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Hybridized Orbitals
When carbon double bonds, the 2s, 2px and 2py orbitals on
carbon form three sp2 hybrid orbitals.
The three hybrid
orbitals form the points
of a triangle.
C
A trigonal planar atom
has sp2 hybridization.
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Double Bonds
H
H
C
H
C
H
The three sp2 hybrid orbitals of carbon and 1s orbitals
of hydrogen make up the σ-framework of ethene.
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Double Bonds
When the double bond is formed between the two
carbons of ethene, a different type of bond is needed
(a π bond). This bond is formed with the remaining
2pz orbitals and is higher energy than the σ bonds.
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