Bonding

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Bonding
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The Properties of a Compound are Different from
the Properties of the Elements that make up that
Compound
Calcium Chloride
Calcium
Chlorine
Copper Chloride
Copper
Chlorine
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Chemical Formula Used to represent the kinds
and numbers of atoms in a chemical compound.
HC2H3O2
Subscript
Be(ClO2)2
Subscript multiplies to all subscripts in
parentheses!

• NaHCO3 MgCl2
• Al(OH)3 Ca(NO3)2

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What must happen for elements to react with each
other?

• Atoms of the elements must collide.
• The valence electrons are what actually collide
  in when elements form compounds.
• This is because the valence electrons are the
  outermost layer.

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Valence Electrons

• The electrons in the outermost energy level of an
  atom
• Responsible for an atoms chemical properties

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LEWIS DOT DIAGRAMS

• A diagram where dots are placed around the
  chemical symbol of an element to illustrate the
  valence electrons

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Octet Rule

• Octet 8
• States that atoms tend to gain, lose or share
  electrons in order to acquire a full set of
  valence electrons.
• For most elements this is 8 valence electrons
• Hydrogen Helium only require 2 valence
  electrons
• The elements are all trying to be like the Group
  18 elements, the noble gases b/c they have 8
  valence electrons
• Atoms form compounds to become stable!

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How do atoms obtain a noble gas configuration?

• By sharing or transferring electrons with other
  atoms
• Example Show how Na Cl can become stable.
• The bond between Na Cl is due to

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ANIONS Have gained electrons and have a
negative charge (nonmetals)
If atoms transfer electrons to form a bond they
become IONS
ION AN ATOM THAT HAS AQUIRED A CHARGE BY
GAINING OR LOSING ELECTRONS
CAIONS Have lost electrons and have a positive
charge (metals)
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Ionic Compound Compound formed from ionic bonds

• Ionic Bond The strong attractive force between
  ions of opposite charge. Occurs when one atom
  transfers electrons to another atom to become
  stable

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EMPIRICAL FORMULA

• Chemical formula for an ionic compound
• Lowest whole number ratio of ions in an ionic
  compound

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Types of elements in an ionic compound

• An ionic bond is formed between a ______________
  and a __________ because
• Ionic bonds are formed between ions of opposite
  charge
• Therefore, ionic bonds form between ____________
  and _____________ because metals form cations and
  nonmetals form anions.

nonmetal
metal
nonmetal
metal
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How do Ionic Compounds Form?

• Electrons are _______________________ in an ionic
  bond because one atom is trying to lose
  electrons to become stable and the other atom is
  trying to gain electrons to become stable

transferred
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EMPIRICAL FORMULA

• Al2O3

Subscript written to the lower right of a
chemical symbol that shows the number of atoms of
that element present in the compound

• 3 WAYS TO DETERMINE AN EMPIRICAL FORMULA
• Use Lewis Dot Diagrams
• Use charges
• Use the Crisscross Method

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DETERMINING THE EMPIRICAL FORMULA BY USING LEWIS
DOT DIAGRAMS TO ILLUSTRATE THE IONIC BOND
1

• Draw the Lewis Dot Diagram for each element
• Use arrows to show the transfer of electrons
  between atoms
• Determine the number of each element necessary to
  make each atom

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PROPERTIES OF IONIC COMPOUNDS

• Made of ions
• Typically a metal and nonmetal(s)
• Crystalline Solids
• Hard yet Brittle
• Strong Interparticle Forces
• High Melting and Boiling Points
• Will conduct electricity when molten or dissolved
  in water

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INTERPARTICLE FORCES Forces of attractions
between neighboring particles (atoms, ions or
molecules)
Strong

• Ionic compounds have __________________
  interparticle forces due to the strong
  electrostatic attraction between the cation(s)
  and anion(s)
• Because of these ________________ interparticle
  forces,
• ionic compounds have _____________ melting
  points.

Strong
high
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CRYSTAL A regular, repeating arrangement of
ions in an ionic compound
The arrangement of ions in an ionic compound
determines the crystal structure (shape) of the
crystal itself.
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CRYSTAL

• CaCl2

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ELECTROLYTE A compound that conducts an
electric current when it is in an aqueous
solution or in a molten state

• http//www.youtube.com/watch?vEBfGcTAJF4o

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IONIC COMPOUNDS

• Ions of opposite charge strongly ___________ each
  other. Ions of like charge strongly
  ______________ each other.
• As a result of this, how are ions arranged in an
  ionic compound?

attract
repel
Positive ions tend to be near negative ions and
farther from other positive ions.
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Metallic Bonding The attraction of free floating
valence electrons for the positively charged
metal ions.Made of just metal atoms

• Pure metals are not simply 1 atom of the metal.
  They are multiple atoms of that metal bonded by a
  sea of electrons.

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Metallic Properties Come From their Sea of
Electrons

• Metallic bonds form from a Sea of Electrons
  The pool of electrons shared by all the atoms in
  a metallic substance

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Malleability The ability to be hammered into
sheets

• Metals are malleable because the metal atoms can
  slide through the electron sea to new positions

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Ductile Able to be pulled into wires

• Metals are ductile because electrons in the sea
  of electrons move to allow atoms to align like a
  wire

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Conductivity

• Electricity is caused by moving electrons
• Metals conduct because the sea of electrons is
  free to move and, therefore, free to conduct
  electricity

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Interparticle Forces

• Metallic bonds have strong interparticle forces.
  For this reason metals
• Are typically solids
• Are crystalline
• Metals are arranged in very compact and orderly
  patterns
• Have average to high melting

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ALLOY A mixture composed of 2 or more elements,
at least 1 is a metal
NAME OF ALLOY MAKE UP EXAMPLE
Stainless Steel 73-79 Fe 14-18 Cr 7-9 Ni
Sterling Silver 92.5 Ag 7.5 Cu
18-karat white gold 75 Au 12.5 Ag 12.5 Cu
14 karat gold 58 Au 14-28 Ag 14-28 Cu
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Covalent Bonding Bonding in which electrons are
shared

• Electrons spend most of their time between the
  atoms.
• The attraction between the nucleus and the shared
  electrons holds the atoms together.

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Molecular Compound

• Compound formed by covalent bonds (from the
  sharing of electrons)

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Covalent Bonds

• Form molecules instead of crystals.
• Molecule The combination of atoms formed by a
  covalent bond

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Types of Elements in a Covalent Bond

• Therefore, covalent compounds are formed between
  2 or more ____________________ because
  _____________ are the type of element that want
  to gain, not lose, electrons.
• In a covalent bond, the atoms share electrons
  because both atoms want to gain electrons.

nonmetals
nonmetals
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Ionic Compound (Metal Nonmetal) or Covalent
Compound (All Nonmetals)
Which type of bond would form between the
following elements? MgCl2 NI3 AlN CO2 F2
SnO2
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How do Covalent Bonds Form?
Two nonmetals share electrons to form a bond
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Covalent Bonds

• Structural Formula Shows the arrangement of
  atoms in a molecule or polyatomic ion

Space Filling Model Ball Stick
Model Structural Formula
O
?
H
H
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LEWIS STRUCTURES

• Uses dashes and dots to show the bonding
  arrangement of atoms in a covalent compound
• Drawn to model the bonding in a covalent
  compound.
• Based on Lewis Dot Diagrams
• Dashes (?) Each dash represents a bond (or 2
  shared electrons)

LONE PAIR
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Single Covalent Bond

• 1 shared pair of electrons between 2 atoms
• Represented by ?
• Example

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Double Covalent Bond

• 2 shared pairs of electrons between 2 atoms
• Represented by
• Example

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Triple Covalent Bond

• 3 shared pairs of electrons between 2 atoms
• Represented by
• Example
• Lone Pairs (??) Represents an unshared pair of
  electrons

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Using Lewis Dot Diagrams to Determine the Lewis
Structure

• Draw the Lewis Dot Diagrams for each atom in the
  Molecular Formula
• Determine how the atoms will SHARE electrons so
  that all atoms are

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(N-A)/2 of Bonds in Molecule

• N of electrons needed to make an each element
  in the compound stable
• N 8 electrons for all elements except H and He
  which need 2 electrons
• A of valence electrons each element in the
  compound has
• There are 2 electrons per bond so we divide the
  of electrons they need to share by 2 to determine
  the number of bonds

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Some General Guidelines

• Carbon is typically in the center of the molecule
• If possible, keep the molecule symmetrical
• Hydrogen the halogens can only accept one
  electron and, therefore, tend to be on the
  perimeter of the molecule
• Sometimes, the formula will help you figure out
  the structure
• Check your work Do all atoms have 8 electrons?
  Does H have only 2 electrons?

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(N-A)/2 of Bonds in Molecule

• NH3 Cl2 CH4

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(N-A)/2 of Bonds in Molecule

• H2CO C2H2 NH4

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Resonance Structures Two or more equally valid
structures of a molecule or polyatomic ion
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Exceptions to the Octet Rule

• 1) Atoms with less than an octet
• Boron may not acquire a full octet, it may only
  obtain 6 electrons--it has only 3 valence
  electrons to start
• Atoms with more than an octet
• Especially phosphorus sulfur
• Molecules with Odd Numbers of Electrons
• Any molecule that has an odd number of available
  electrons, especially compounds of Nitrogen

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Coordinate Covalent Bond

• A covalent bond in which one atom contributes
  both bonding electrons

?
?
O
C
?
C
O
?
?
?
?
?
?
?
?
?
?
?
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Properties of Covalent Compounds

• Made of molecules
• All nonmetals
• Often liquids or gasses
• Brittle if solid
• Weak Interparticle Forces
• Low Melting and Boiling Points
• Do not conduct electricity when molten or
  dissolved in water

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More Properties

• Covalent compounds have ______________
  interparticle forces
• Because of these _______________ interparticle
  forces, covalent compounds have low melting and
  boiling points
• Bond Dissociation Energy The energy needed to
  break the bond between two covalently bonded
  atoms
• A high bond dissociation energy corresponds to a
  strong covalent bond

weak
weak
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Ionic Covalent Metallic
Type of Elements
State
Electrons are
Hard or brittle?
Melting Points
Made of
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MOLECULAR GEOMETRY

• VSEPR THEORY
• Valence Shell Electron Pair Repulsion Theory
• In small molecules, the pairs of valence
  electrons are arranged as far apart from each
  other as possible

YES!!!
NO!!!
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Ball-and-Stick Models

• Drawings that represent molecular compounds. The
  balls are used to represent atoms and the sticks
  are used to represent bonds.

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VSEPR Theory Electrons repel (bonds lone
pairs move as far apart as possible)
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Bond Angles

• The geometric angle between 2 bonds

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Other Shapes
Octahedral SF6
T-Shaped ICl3
Square Planar XeF4
Trigonal Bypyramidal PF5
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EXAMPLES

• CO2 PF3 CBr4

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Bond Length

• Different pairs of atoms form bonds with
  different lengths
• Not represented in a ball-and-stick model
• As you move down a group on the periodic table,
  the atoms form longer bonds because the atoms
  become larger
• Multiple bonds are shorter than single bonds
• The more electrons there are, the more attraction
  there is for the opposite nuclei
• Bonds are electrical glue

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Electronegativity The ability of an atom to
attract electrons when the atom is in a compound

• Shows how much an atom will attract valence
  electrons
• The higher the electronegativity the more an atom
  attracts the electrons towards it

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?EN

• The difference between two atoms
  electronegativities determines the type of bond
  formed between those two atoms
• ?EN EN1-EN2
• ? is the Greek Letter delta and means change
• ?EN is always positive (always subtract the
  smaller number from the larger number)
• Example Calculate the ?EN between Cesium and
  Fluorine

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You can think of bonding as a tug-of-war for
electrons between atoms

• The electronegativity of the atom tells you how
  hard that atom is pulling for the electrons

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Ionic Bond

• When one atom wants the electrons so much more
  than the other atom that it pulls the electron
  off the other atom (a tug-of-war where one side
  wins)
• ?EN gt 2.0 (greater than 2.0)

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Nonpolar Covalent Bond

• Like an even tug-of-warboth atoms want the
  electrons equally so the electrons stay between
  them
• ?EN lt 0.4 (less than 0.4)

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Polar Covalent

• One atom wants the electrons more than the other
  but not enough to pull it all the way towards
  itselflike an uneven tug-of-war
• ?EN is between 0.4 2.0

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Electronegativity Difference
?EN EN1 EN2
Nonpolar
Polar
Ionic
0.0
0.4
2.0
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Polar Covalent Bonds

• Polar bonds have partially charged atoms due to
  the unequal sharing of electrons
• Dipole A partial charge on an atom.
• If the ?EN on a bond is between 0.4 and 2.0 then
  that bond has a dipole (partial charge)
• This is because one atom wants the electrons more
  than the other but not enough to cause a complete
  transfer

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DIPOLE

• ? Symbol for a dipole or a partial charge
• Used to label the partial charges on a polar bond
• Two ways to label the dipoles (partial charges)
  on a polar bond

C-Cl
?
?-
F
H
F
H
or
2.1
4.0
?EN 4.0-2.10.9 (polar)
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Images of Polar/Nonpolar
Nonpolar Polar Polar
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To determine the polarity of a molecule

• Does the molecule have only nonpolar bonds?
• YES It is nonpolar
• Is the molecule completely symmetrical in all
  dimensions?
• YES It is nonpolar
• If the molecule contains at least 1 polar bond
• and is not completely symmetrical in all
• dimensions, then the whole molecule is POLAR

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Polarity of Carbon Dioxide

• CO2

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Polarity of Ammonia

• NH3

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• H2O

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• CH4

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The Periodicity of Electronegativity
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Electronegativity Differences Bonding

• The greater the difference between the
  electronegativities of the bonding atoms, the
  more unequally those atoms share electrons
• The symbol for electronegativity difference ?EN

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Ionic Bonds

• ?EN is gt 2.0
• This is because one atom wants the electrons much
  more than the other
• Because of the high ?EN you can assume that the
  electron on the less electronegative atom is
  transferred to the other atom

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Nonpolar Covalent Bonds

• ?EN is lt 0.4
• This is because both atoms have almost an equal
  attraction for the electrons
• Because of the low ?EN the atoms are shared
  equally
• These molecules are gases or low-boiling point
  liquids at room temperature
• These bonds are also known as Nonpolar Covalent
  Bonds

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Example

• Label the dipoles on a C?Cl bond.
• Could also use vectors to label a polar bond.
• Example Use a vector to label the dipoles on a
  C-Cl bond.

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To determine the polarity of a molecule

• Draw the Lewis Structure of the Molecule with the
  correct geometry
• Use electronegativity values to determine if any
  of the individual bonds are polar. If so, label
  the dipoles.
• Using vector addition, check to make sure the
  dipoles do not cancel out.
• If at least 1 vector/dipole does not cancel out,
  the molecule is polar.
• If all the vectors/dipoles do cancel out, the
  molecule is nonpolar
• Vectors will only ALL cancel out if the molecule
  is linear or tetrahedral and completely
  symmetrical!

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VECTOR ADDITION

• Involves vector addition.

0


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Polarity of Ammonia

• NH3

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• H2O

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IodineI2
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Methanol CH3OH
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Dimethyl Ether (CH3)2O
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EXAMPLES

• CO2 CH4 CH2O

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Properties of Polar Covalent Bonds

• Higher Boiling Points than Nonpolar Covalent
  Bonds
• Molecules can stick together and form puddles
• Hydrophilic ionic polar (mix easily with
  water)
• Like dissolves like

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Large Molecules

• In a large molecule the polarity oftentimes
• helps determine the molecules shape.

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ATTRACTIONS BETWEEN MOLECULES

• Responsible for determining whether a
• molecular compound is a gas, liquid or
• solid at a given temperature.

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Van der Waals Forces

• Consist of Dipole Interactions Dispersion
• Forces

• Dispersion Forces Caused by the motion of
  electrons
• Weakest of all molecular interactions

Dipole Interactions Occur when polar molecules
are attracted to one another Similar to but much
weaker than ionic bonds
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Hydrogen Bonds

• The attraction to a hydrogen atom already
• bonded to a strongly electronegative atom
• Strongest of intermolecular forces.
• Extremely important in determining the properties
  of water and biological molecules