Chapter 8 Chemistry 1

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Chapter 8 Chemistry 1

• Covalent Bonding

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Why do atoms bond

• Its all about stability
• Atoms want to achieve the stable octet of the
  noble gases
• Ionic and metallic bonds achieve this octet
  through an exchange of electrons
• The exchange occur between a metal ion (cation)
  and a non-metal ion (anion)
• Covalent bonds are different

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What is a covalent bond

• A covalent bond occurs when atoms share electrons
• Covalent bonds occur between two non-metals
• Valence electrons play a role in covalent bonds

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How to determine a covalent bond

• In the case of hydrogen combining to form H2
• Each hydrogen has 1 valence electron
• In order to achieve the noble gas configuration
  of helium, they each need two valence electrons
• H2 achieves this by sharing their valence
  electrons and forming a bond
• http//www.visionlearning.com/library/flash_viewer
  .php?oid1348mid55

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What happens in a covalent bond

• Electrons are shared between the two atoms
• Each atom thinks it has a full outer shell
  containing 8 valence electrons
• The sharing of electrons is what makes the bond
  and holds the atoms together
• Water is a covalently bonded molecule

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Water

• Hydrogen needs 2 electrons to fill its outermost
  shell
• Oxygen needs two electrons to fill its outermost
  shell

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Lewis Structure of Water

• http//web.visionlearning.com/custom/chemistry/ani
  mations/CHE1.7-an-H2Obond.shtml

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Lewis Structure of Carbon Dioxide CO2

• Carbon has four valence electrons, and oxygen has
  six.
• Each pair of shared electrons forms a single bond
• There are two bonds (a double bond) between the
  carbon and each oxygen

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Covalent and Polar Covalent Compounds

• http//link.brightcove.com/services/player/bcpid91
  13583001?bctid1396941780
• Covalent Bonding
• http//www.saskschools.ca/curr_content/chem20/covm
  olec/covintro.html

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Covalent Bonding Tutorial

• "C\Program Files\Covalent Bonding\chemsim3.exe"

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Determining a Lewis Structure

• Write the symbol for the central atom in the
  molecule
• Join the other atoms using dashes
• Two shared electrons is a single bond
• Calculate the number of bonds
• The formula to use is   

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Determining Lewis Structure contd

• Add dashes to your diagram to make the number of
  bonds calculated in step 3 equal to the number of
  dashes shown in the diagram
• Add dots to obey the octet rule
• Do a final count that all atoms obeyed the octet
  rule

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Practice

• http//www.saskschools.ca/curr_content/chem20/covm
  olec/covlewis.html

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You Try It

• What would the formula be for a compound
  containing carbon and fluorine
• What is the formula for a compound containing
  nitrogen and oxygen
• Carbon and hydrogen?
• Antimony and bromine?
• Chlorine and oxygen?

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Electronegativity Table
Electronegativity Table of the Elements

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Determining a Bond From Electronegativities

• Calculate the difference between the
  electronegativities of the atoms involved in the
  bond
• When differences are 1.7 or greater the bond is
  ionic
• When differences are between 0.3 and 1.7, the
  bond is polar covalent
• When the difference is less than 0.3 the bond is
  non-polar covalent

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Non Polar Covalent Bond

• When two fluorine atoms bond
• Each atom has a high attraction for bonding
  electrons
• Both attract them equally. (We've got two
  well-matched Boston Terriers pulling on this
  sock.)
• The electronegativity difference between the
  atoms is zero, and the bond is pure covalent.

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Polar Covalent

• F2O for example results in a bond that is
  polarized
• Bonding electrons spend more time around the
  fluorine than the oxygen because fluorine has the
  higher electronegativity
• Fluorine end of the bond has a partial negative
  charge
• The oxygen end has a partial positive charge
• The electronegativity difference is 0.5, so the
  bond is best described as polar covalent. (Think
  of a Boston Terrier pulling against a German
  Shepherd).

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Ionic

• The bond between fluorine and lithium results in
  a bond with a much larger electronegativity
  difference
• 4.0 for F minus 1.0 for Li is 3.0
• This bond is best described as an ionic bond.

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Calculating the Electronegativity Difference

• Predict the bond that will form between H and S
• Between C and H?
• Between Na and S?
• Identify each as polar or nonpolar
• SCl2
• CS2
• CF4

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Resonance Structures

• A resonance structure occurs when there is more
  than one valid Lewis structure for a molecule or
  ion
• Resonance structures differ only in the position
  of the electron pairs, never in the position of
  the atoms

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Lewis Structure of Ozone (O3)

• Calculate the number of bonds
• What is the number of electrons each oxygen wants
  to have
• What is the number of electrons each oxygen has
• Calculate the number of bonds using the formula

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Lewis Structure of Ozone (O3) contd

• Begin by drawing the basic structure
• Then add the third bond
• However, we cannot be sure if the double bond is
  on the left or the right
• Draw the resonance structures for ozone

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Resonance Structures of the Nitrate (NO3-) ion

• Calculate the number of bonds

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Resonance Structures of the Nitrate (NO3-) ion

• Draw the basic atom
• Insert the valence electrons
• Do all the atoms have an octet?

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Resonance Structures of the Nitrate (NO3-) ion

• Add bonds so that each atom has an octet
• Are there any other ways we can draw this atom?
• If so, these resonance structures must also be
  drawn

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Resonance Structures of the Nitrate (NO3-) ion

• Below are all three possible structures for this
  ion
• These are the resonance structures of nitrate

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You Try It

• Draw resonance structures for
• SO2
• SO32-
• CO32-

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Naming Covalent Compounds

• Simple covalent compounds are generally named by
  using prefixes to indicate how many atoms of each
  element are shown in the formula
• The ending of the last (most negative) element is
  changed to -ide.

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Prefixes

• The prefixes used are mono-, di-, tri-, tetra-,
  penta-, hexa-, and so forth
• The mono- prefix is not used for the first
  element in the formula
• The "o" and "a" endings of these prefixes are
  dropped when they are attached to "oxide."
• Monoxide
• Hexoxide
• Pentoxide

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Table of Prefixes
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Which Element is First?

• Generally, they are in the same left-to-right
  order that they have on the periodic table
• Except that you would have to squeeze hydrogen in
  between nitrogen and oxygen

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Name the following compounds

• PH3
• phosphorus trihydride
• CO
• carbon monoxide
• HI
• hydrogen monoiodide 
• N2O3
• dinitrogen trioxide

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What is the Formula

• Carbon Tetrachloride
• CCl4
• Dinitrogen Pentoxide
• N2O5
• Silicon Tetrabromide
• SiBr4

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Chemical Bonds Ionic and Covalent

• The World of Chemistry Everyday Chemistry
• http//www.learner.org/vod/vod_window.html?pid800