Drawing covalent bonds

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Drawing covalent bonds

• Draw the following covalent compounds in your
  notebooks now
• NH3
• CH4
• CO2

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2/8/11 E Day

• Objective To understand how structure of
  compounds determines their function
• Do Now What is the shape of the following
  molecules CH4, H2O, O2
• Today
• Review of Ionic Covalent Compounds
• Polarity

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Three dimensional chemistry

• REMEMBER
• electrons same charge repel each other
• unshared electrons also repel
• because electron pairs repel, molecules adjust
  their shape so that the valence electron pairs
  are as far apart as possible VSEPR theory

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Molecular geometry

• linear triatomic (carbon dioxide, CO2)
• trigonal planar
• tetrahedral (methane, CH4)
• all possible bonds are attached to atoms (no lone
  pairs on central atom)
• bent triatomic (water)
• pyramidal (ammonia, NH4)
• lone pairs on central atom in these two

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Bent (water, H2O)
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Pyramidal (ammonia, NH4)
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Methane (tetrahedral, CH4)
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Daily Agenda

• Bonding Overview
• Notes - Polarity
• CW IF Polarity WS, Models Lab
• HW 8.3 Guided Reading

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Bonding Overview
Electronegativity Increases!

• Atoms bond to satisfy the octet rule
• Ionic Bonding
• Metals Nonmetals
• Form Ions BECAUSE of HUGE difference in
  electronegativity!
• Molecular Bonding
• Nonmetals/metalloids
• SHARE e- BECAUSE of SMALL difference in
  electronegativity!

Blue Metals Yellow NonMetals/metalloids
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Bonding Overview

• Octet Rule
• Atoms gain/lose/share electrons to become like
  their nearest NOBLE GAS
• When atoms satisfy octet rule they BECOME MORE
  STABLE
• Results in a DECREASE of potential energy
• It is easier to lie down than to stand up,
  bonding is Natures way of allowing elements to
  lie down.

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Bonding Overview

• Ionic Bonding
• Formulas are definitive
• Metals/nonmetals ALWAYS gain or lose fixed
  numbers of electrons, so charges are ALWAYS the
  same
• Criss cross charges to make formulas
• Name compounds metal nonmetal ide or metal
  polyatomic ion

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Ionic Bonding Review

• Structures are definitive
• Cations ( metal ions) and anions (- non metal
  ions) ATTRACT
• Arrange themselves into highly organized 3-D
  structures called CRYSTALS
• High MP Conduct electricity when molten or
  dissolved in water

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Bonding Review

• Molecular Bonding
• Formulas are not set
• Nonmetals/metalloids have similar
  Electronegativity values, so electrons are shared
  NO IONS FORMED
• We have to be GIVEN either formula or name
• Formulas use prefixes to determine subscripts
• Naming use prefixes to show atoms of each
  element

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Bonding Review

• Molecular Bonding
• Structures are not set
• Nonpaired valence electrons will ALWAYS form
  bonds
• Each elements will form enough bonds in order to
  satisfy the octet rule
• Single, double or triple bonds
• (Needed Available)/2 bonds formed by each
  element (OR THE NUMER EQUALS THE CHARGE!)

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Bonding Review

• Molecular Bonding
• Structures are NOT definitive
• Bonded/nonbonded pairs of electrons REPEL each
  other
• Bonded/nonbonded pairs of electrons will spread
  out AS FAR AWAY as possible to form shapes
  VSEPR Theory

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Bonding Review

• Non central bonding atom OR no lone pairs around
  CBA - LINEAR
• Four bonded/nonbonded electron pairs around CBA -
  TETRAHEDRAL
• Tetrahedron
• Pyramidal
• Bent
• Three bonded electron pairs around central bonded
  atom - TRIGONAL

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Ionic vs. Covalent bondsand electronegativity

• What if one atom has a greater electronegativity
  than the other but not enough strength to pull
  the electron away all together (form an ionic
  bond)?
• We land somewhere in the middle with
• polar covalent bonds
• non polar covalent bonds

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Polar vs. Nonpolar Covalent Bonds

• Electronegativtiy measures the nucleus ability
  to attract electrons
• When bonding atoms approach each other a tug of
  war beginsExample HCl
• Cl nucleus is stronger so bonding e- are closer
  to Cl

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Dipole

• In a polar molecule, one end is slightly negative
  and the other end is slightly positive
• In chemistry, this type of molecule is referred
  to as a dipole.
• EXAMPLE Water!

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Non polar covalent bonds

• Forms when atoms share electrons equally (like in
  the H2 example)
• Each atom has equivalent electronegativity values
• OR molecule is symmetrical!
• linear (CO2, CS2)
• trigonal (BF3)
• tetrahedron (CF4, CCl4)

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Non polar covalent bonds
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Polar vs. Non-polar vs. Ionic

• Online Text Video
• C2H6 non-polar
• Water polar
• Na and Cl-

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Intermolecular Forces

• Molecular solids exist because of attractive
  forces between MOLECULES
• Dipole-Dipole - between polar molecules. MIDDLE
• Dispersion - between non-polar molecules. WEAKEST
• Hydrogen Bonding - between molecules with H, N or
  O or F. STRONGEST

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Daily Agenda

• Submit Completed Lab Packet
• Molecular Review - Questions?
• HW - Molecular Exam tomorrow!

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Daily Agenda

• Submit 8.3 Guided Reading
• VSEPR Quiz
• Molecular Models Lab
• Molecular Review - Questions?
• HW - Molecular Exam tomorrow!