CHEM 1405

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CHEM 1405

• Class Meeting 8

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Assignments and Reminders

• Reading Assignment
• Chapter 4 by Tuesday, Jan 31st
• Homework Problems Due Today Feb 9th
• Chapter 3 problems 2, 4, 8, 10, 12, 14, 16, 18,
  20, 30, 32, 42, 44
• Homework Problems due next Thursday Feb 16th
• Chapter 3 problems 46, 50,52,54,56,58,60, 62
• Reminder Test 1 is in the testing center
• You must complete this exam before 11 am on
  Tuesday Feb 14th
• Class website
  http//iws.ccccd.edu/jstankus/

Please use only one side of the page when
submitting Homework
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Polyatomic Ions

• Many compounds contain both ionic and covalent
  bonds
• Example Sodium Hydroxide NaOH
  

Covalent Bond
Na
A polyatomic ion is a charged particle containing
two or more covalently bonded atoms
Ionic Bond
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Polyatomic Ions Examples
O
H
O
-
-
-
C
C
H
O
O
C
O
Acetate Ion
Carbonate Ion (note -2 Charge)
H
H
-
N
H
H
O
N
O
Nitrite Ion
Ammonium Ion
H
Polyatomic ions have both covalent bonds (dashes)
that hold the atoms together as a group and ionic
charges ( or -) that allow them to interact with
other ions to form compounds.
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Polyatomic Ions

• Charged groups of atoms that remain together
  through most chemical reactions

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Polyatomic Ions

• Working with polyatomic ions is just like
  Monatomic ions
• Example Ammonium Chloride
• NH4 Cl- ? NH4Cl-

NH4Cl
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Molecular Shape

• Determine reactive, chemical and physical
  properties
• Very important in biological systems
• Must draw electron-dot diagram to predict shape
  of molecule
• Look at central atom

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Valence Shell Electron Pair Repulsion (VSEPR)
Theory

• Electron pairs arrange themselves to minimize
  repulsion

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Shape of Molecules

• Draw electron-dot structure
• Count number of bonding and nonbonding pairs of
  electrons
• Determine number of electron sets
• Sketch shape

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Basic Shapes

• Electron pairs arrange themselves to minimize
  repulsion

Linear 180
2 Sets of electrons
Trigonal Planar 120 in plane of page
3 Sets of electrons
Tetrahedral 109.5
4 Sets of electrons
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Nonbonding Pairs Effect on Shape
4 Sets of electrons
4 Bonding Pairs 0 Lone Pairs (LP)
Tetrahedral
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Lone Pairs Effect on Shape
4 Sets of electrons
3 Bonding Pairs 1 Lone Pairs (LP)
Pyramidal
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Lone Pairs Effect on Shape
4 Sets of electrons
2 Bonding Pairs 2 Lone Pairs (LP)
Bent
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Possible Shapes
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What is Shape of SCl2
1. Electron dot structure
2. Count sets 2 bonded atoms 2 non
bonding pairs
Total of 4 sets
3. The four sets get as far apart as possible
a tetrahedral arrangement
4. Two of the sets are nonbonding pairs
-therefore SCl2 is a bent molecule with 109.5
angle
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Unequal sharing
H-Cl example

• Chlorine atoms have a greater attraction for a
  shared pair of electrons than do hydrogen atoms
  they are more electronegative than hydrogen
• Bond is polar covalent bond
• not an ionic bond but unequal sharing

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Polar Covalent Bonds
d are deltas indicating partial charge

• Hydrogen Chloride readily dissolves in water to
  form hydrochloric acid

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Electronegativity

• Fluorine most electronegative element

Electronegativity Increases
Electronegativity Increases
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Categorizing Bonds by Electronegativity Difference
Increasingly Polar
Nonpolar
0
1.7 -1.8
0.4
Ionic
Covalent
Example H-Cl Cl 3.0
H 2.1 Difference 0.9 Polar Covalent Bond
Elecronegativity Difference
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Shapes and Properties
d-
d-
d
d-
d
d-
d
Net Polarity
d
2.6
2.6
3.5
2.2
CO2
H2S
Bond Polarity adds up Polar Molecule
Bond Polarity Cancels out Nonpolar Molecule
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Shapes and Properties

• Polar molecule has separate centers of positive
  and negative charge

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Review
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Ions

• When an atom gains or loses electrons, it becomes
  charged and is called an ion.
• Tend to go to a noble gas configuration
• Ionization energy is the energy required to
  remove the least tightly bound electron from a
  ground-state atom (or ion) in the gaseous state.
• Creates a Positive Ion
• Electron affinity is the energy change that
  occurs when an electron is added to an atom in
  the gaseous state.
• Creates a Negative Ion

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Types of Chemical Bonds

• Ionic bonds are attractive forces between
  positive and negative ions, holding them together
  in a solid crystal. Electron is transferred.
• A covalent bond is a bond formed by a shared pair
  of electrons between atoms

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Valence Electrons and Core Electrons
The valence shell is the outermost shell of
electrons of an atom.
Mg example
The electrons in the valence shell determine the
chemical properties
1s22s22p6
3s2
Ne
3s2
The electrons in the inner shells are the core
electrons and dont affect the chemical
properties strongly
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Lewis Dot Structures
The valence shell is the outermost shell of
electrons of an atom.
Mg example
1s22s22p6
3s2
Ne
3s2
2 electrons in the valence Shell
Use dots to represent Valence Electrons
Mg
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Atomic Electronic
Valence Lewis Element Number
Configuration Electrons
Dot Structure
Hydrogen 1 1s1 Helium 2 1s2 Lithium 3 1s22
s1 Beryllium 4 1s22s2 Boron 5 1s22s22p1 C
arbon 6 1s22s22p2 Nitrogen 7 1s22s22p3 Oxygen
8 1s22s22p4 Fluorine 9 1s22s22p5 Neon 10 1s2
2s22p6 Sodium 11 1s22s22p63s1 Magnesium 12 1s2
2s22p63s2 Aluminum 13 1s22s22p63s23p1 Silicon
14 1s22s22p63s23p2 Phophorus 15 1s22s22p63s23p3
H He Li Be B C N O F Ne Na Mg Al Si P
1 2 1 2 3 4 5 6 7 8 1 2 3 4 5
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Ions

• When an atom gains or loses electrons, it becomes
  charged and is called an ion.
• Tend to go to a noble gas configuration
• Ionization energy is the energy required to
  remove the least tightly bound electron from a
  ground-state atom (or ion) in the gaseous state.
• Creates a Positive Ion
• Electron affinity is the energy change that
  occurs when an electron is added to an atom in
  the gaseous state.
• Creates a Negative Ion

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ElectronDot Structures for Ions

• Add electrons for anions

Chlorine atomic number 17 1s22s22p63s23p5
7 Valence electrons
Add electron to form ion
-
Chloride ion atomic number 17 1s22s22p63s23p6
8 Valence electrons
Now has full shell with similar electronic
configuration to Argon --Stable noble gas
configuration
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ElectronDot Structures for Ions

• Remove electrons for cations

Na
Sodium Atomic number 11 1s22s22p63s1
1 Valence electron
Remove electron to form ion

Na
Sodium Ion Atomic number 11 1s22s22p63s0
Now has full shell with similar electronic
configuration to Neon --Stable noble gas
configuration
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Sodium Reacts with Chlorine

• Sodium dropped in flask filled with chlorine gas
• Produces sodium chloride (i.e., table salt)
• Chlorine extracts electron from sodium

-

Na
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More Ionic Compounds

• Compound of Magnesium and Chlorine

Remove 2 electrons
Add 1 electron
Add 1 electron
-
-
Mg2
Charge is not balanced
Need two Chloride ions to balance charge on
Magnesium ion
MgCl2
Magnesium Chloride
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Naming Ions

• For cations, simple positive ions
• Add the word ion
• Examples Na sodium ion
• Al3 aluminum ion
• For anions, simple negative ions
• Change the usual ending to -ide
• Examples Cl chloride
• S2 sulfide

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Naming Binary Ionic Compounds

• Two components in compound

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Binary Compounds

• Zinc and Oxygen

Zn
O
O2-
Zn2
Zn2
O2-
2
2
Zn2O2
ZnO
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Covalent Bonds

• Bond formed by a shared pair of electrons
• Gives atom an octet of electrons
• Shared pair of electrons bonding pair
• Other electrons not involved in bonding
  nonbonding pairs

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Covalent Bonds example
Chlorine does not occur in nature as an isolated
atom
Bonding Pair
Lone Pair
Chlorine atoms share electrons to get full shell
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Dash Notation for Covalent bonds

• Since the dots for electrons get crowded, dashes
  can be used to represent a covalent bond

H
H
H2
H
H
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Multiple Covalent bonds
Only 7 electrons does Not meet Octet Rule!
Need to share Another pair of electrons
O
Sharing One Pair of electrons One Covalent
Bond
O
O
O
A Double Bond can be represented by a double line
Sharing Two Pairs of electrons Two Covalent
Bonds A Double Bond
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Multiple Covalent bonds
Nitrogen
N
N
Sharing Three Pairs of electrons Three
Covalent Bonds A Triple Bond
N
N
A Triple Bond can be represented by a Triple line
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Naming Covalent Compounds

• Common Names
• Water H2O
• Ammonia NH3
• Methane CH4

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Naming covalent compounds
Prefix Number of atoms Mono- 1 Di- 2 Tri- 3
Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa-
8 Nona- 9 Deca- 10

• Use prefix to Denote number of each type of atom

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Naming exercises

• Carbon Tetrachloride
• 1 Carbon
• 4 Chlorines
• CCl4
• Tetraphosphorous Hexoxide
• 4 Phosphorus
• 6 Oxygens
• P4O6

Tetra- Indicates four Chlorine Atoms
Tetra- Indicates four Phosphorus Atoms
Hexa- Indicates six Oxygen Atoms
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Skeletal Structure

• order in which atoms are attached to one another
• Rules to build skeletal structures
• H forms only single bonds
• Polyatomic ions have the least electronegative
  atom as the central atom
• Except hydrogen

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Draw Electron-Dot Formula

• Determine total number of valence electrons
• Write skeletal structure and connect atoms by
  dashed line
• Give outer atoms an octet of electrons
• Subtract number of electrons assigned

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• Add remaining electrons to central atom
• If central atom does not have an octet, form
  multiple bonds using nonbonding electrons from
  outer atoms

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Number of Covalent Bonds/Element

• Follow the electron-dot rules for the following
  elements

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Free Radicals

• Have odd number of electrons
• One unpaired electron
• Tend to be very reactive
• Nitrous oxide (NO) common radical
• Key component in smog