Types of Chemical Bonds

1
Types of Chemical Bonds
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IONIC BONDS

• Occur between an element with low ionization
  energy (a metal) and an element with high
  ionization energy (a non-metal).
• An actual transfer of electrons from the metal
  (becoming a cation) to the non-metal (becoming an
  anion) occurs.
• This transfer results in the formation of 2
  oppositely charged ions.
• The electrostatic interaction between the 2 ions
  holds the compound together.
• ie. NaCl and MgBr2

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Properties of Ionic Compounds

• Solids at room temperature because the attraction
  between the ions is very strong.
• The intramolecular forces are the same as the
  intermolecular forces (i.e. the electrostatic
  attraction of oppositely charged ions)
• Atoms are arranged in a highly ordered crystal
  lattice structure which maximizes the attractive
  forces between oppositely charged ions and
  minimizes the repulsion between like charged ions
  (the crystal structures are determined
  experimentally using X-ray crystallography).
• Most are soluble in water (the ions will
  dissociate break apart in water).
• Will conduct electricity as a liquid or aqueous
  solution because the ions are free to move to
  oppositely charged electrodes.

4
COVALENT BONDS

• Occur between 2 atoms with high ionization
  energies (i.e. 2 non-metal atoms).
• Result from a sharing of electrons to obtain a
  full outer energy level (octet rule).
• Not all sharing of electrons is equal. A measure
  of an atoms ability to pull on a shared pair of
  electrons is called electronegativity.
• The greater the difference in electronegativities
  the more unequal the sharing. ?EN the
  difference in electronegativities.
• The trend in electronegativities on the periodic
  table follow most other trends. Low in bottom
  left, high at top right.
• The actual values are listed on the periodic
  table.

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Types of Covalent Bonds

• If the electronegativity difference between the
  two atoms is less than 0.4, the bond is a true
  covalent bond and the electrons are shared
  equally.
• If the electronegativity difference between the
  two atoms is between 0.4 and 1.7, the bond is
  polar and there is an unequal sharing of
  electrons.
• If the electronegativity is greater than 1.7, the
  bond exhibits more of an ionic character.

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Types of Covalent Molecules

• Molecules can be either polar or non-polar.
• Just like a bond, an area of a molecule can have
  excess negative charge and an area of deficient
  negative charge.
• Two factors determine the polarity of a molecule
  SHAPE and BOND TYPE

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Determining Molecule Shape

• The 3D shape of the molecule can be approximated
  by building a model.
• First draw a Lewis dot diagram of the molecule,
  trying to have all molecule obtain a full octet
  (8 electrons in the highest energy level)
• Use a molecular model kit to construct the
  molecule.

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Model Building
Molecule Lewis Structure Sketch of Molecule Name of Shape
H2
Cl2
O2
CH4
NH3
H2O
CO2
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Determining Types of Bonds

• Calculate the ?EN for each of the bonds within
  the molecule and draw an arrow towards the atom
  with the higher EN.

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Putting it Together

• The molecule will be polar if it is asymmetrical
  and contains polar covalent bonds. ie. NH3
• The molecule will be non-polar if it is
  symmetrical and contains either polar covalent
  bonds or true covalent bonds.
• ie. CCl4 and F2

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Properties of Non-Polar Covalent Compounds

• Have low melting and boiling points and are
  usually gases at room temperature. This is due
  to the low intermolecular forces that exist in
  these molecules (London Dispersion Forces only).
• If solid at room temperature, the solid is
  usually soft and waxy.
• Soluble in non-polar solvents such as ethers.
• Will not conduct electricity in any form due to
  the fact that there are no ions present.

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Properties of Polar Covalent Molecules

• Since these compounds exhibit polarity or
  dipoles, their intermolecular forces will be
  greater than non-polar covalent compounds (the
  presence of dipole-dipole forces and possibly
  H-bonding).
• These compounds will have higher melting and
  boiling points and are more likely to be liquids
  or solids at room temperature (may even exhibit a
  crystal lattice like sugar).
• Will dissolve in polar solvents if H-bonding is
  present (sugar in water).
• Will not conduct electricity to any appreciable
  degree (only ionize to a very small degree)