CHEMICAL BOND FORMATION

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CHEMICAL BOND FORMATION
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Ionic Bonds

• an electrostatic attraction between
• ions -- usually the reaction between a metal and
  nonmetal. Cause very
• high melting points and usually a
• solid state since the attraction is SO
• strong that the ions are VERY close
• together in a crystal formation.

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Covalent Bond

• Bond orbital is more or less (polar
• or non-polar) evenly distributed and
• the electrons are shared by two
• nuclei.
• (Elements lie close to one another
• on the table.)

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Electronegativity (En)

• The ability of an atom IN A
• MOLECULE meaning its
• participating in a BOND to attract
• shared electrons to itself. Think tug
• of war.

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• Linus Paulings Scale
• Nobel Prize for Chemistry Peace

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• Whats the trend?
• Fluorine is the most En (Highest Zeff and
  smallest so that the nucleus is closest to the
  action)
• Francium is the least En (Lowest Zeff and largest
  so that the nucleus is farthest from the
  action)

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• Use the difference in En to
• determine the type of bond formed.

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• a. Covalent , equally shared electrons
• b. Polar Covalent, slight /- poles
• c. IONIC, electrons are transferred from one atom
  to another

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• The polarity of a bond can be
• estimated from ?E/Highest E.
• Range is 0 for pure covalent bonds,
• to 1 for completely ionic bonds.

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Exercise 1 Relative Bond Polarities

• Order the following bonds according
• to polarity
• HH OH ClH
• SH FH

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Solution
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Practice Problems

• Using only periodic trends of electronegativity,
  predict the order of increasing electronegativity
  difference between following bonds
• C-F Si-F Ge-F
• S-F S-Cl S-Br
• Ti-Cl Si-Cl As-Cl
• Ga-Br Sb-Br Tl-Br Mg-Br

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Solutions

• Ge-F Si-F C-F
• S-Br S-Cl S-F
• Ti-Cl Si-Cl As-F
• Tl-Br Sb-Br Ga-Br Mg-Br
• Study Guide Problems to try Ch. 8 4-10 43-46

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What is a DIPOLE and what does it mean?

• A Dipole is Di 2 and pole - end
• In a diatomic molecule like H-F there is partial
  positive and partial negative charge
• To show the dipole we draw an arrow pointing at
  the negatively charged particle.
• H-F the tail starts at the more positive end

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Examples and steps

• Look up E. N. for each atom
• Draw the molecule in 3-d (yes you have to do this
  again)
• Determine the net polarity on each bond
• Draw the dipoles, with correct direction
• HI CHCl3 CF2I2 N2

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Solutions

• H-I H2.1 I2.5
• C 2.5 H2.1 Cl3.0
• H
• C
• Cl Cl Cl
• N-N N3.0 Diff 0 no dipole
• I
• C 2.5 l 3.0 F 4.0 C
• F
  F I
• Problems to try in study guide 11-13 and 47-48