Chapter 6 SHAPES OF MOLECULES & INTERMOLECULAR FORCES

• Why do molecules have different shapes?

  Bonds contain electrons which repel each other resulting in different shapes
• What do lone pairs do to the shape of a molecule?

  Lone pairs push the bonds closer together and further away from themselves
• What is the bond angle in a tetrahedral molecule?

  109.5
• What is the bond angle in a pyramidal molecule?

  107
• What is the bond angle in a non-linear molecule?

  104.5
• What is the bond angle in a linear molecule?

  180
• What is the bond angle in a trigonal planar molecule?

  120
• What is the bond angle in a octahedral molecule?

  90
• What is the bond angle in a square planar molecule?

  90
• What is the bond angle in a trigonal bipyramidal molecule?

  120 (trigonal) & 90 (bipyramidal)
• Which shapes of molecules have lone pairs?

  Pyramidal, non-linear, square planar
• What is electronegativity?

  Ability for an atom to attract electrons towards itself in a covalent bond
• Which element is the most electronegative?

  Fluorine
• What does a big difference in electronegativity mean?

  The more ionic it is
• How do covalent bonds become polar?

  If there is a big difference in electronegativity between the 2 atoms then the molecule becomes polar because the electron pair in the bond is drawn towards the more electronegative atom
• What happens to symmetrically arranged polar bonds?

  There is no overall polarity
• How can you tell which elements are electronegative?

  The further up and right in the period table, the more electronegative the elements (excluding the noble gases)
• How do induced dipole-dipole forces form?

  When atoms or molecules move near each other because electrons move from one end of the orbital to the other
• How are induced dipole-dipole forces different to covalent bonds?

  Induced dipole-dipole forces hold MOLECULES together whereas covalent bonds hold ATOMS together
• When do permanent dipole-dipole forces form?

  Exist in molecules with polarity - weak electrostatic forces (these molecules also have induced dipole-dipole forces)
• When do hydrogen bonds form?

  Between a hydrogen atom and a lone pair from the 3 most electronegative elements (N O F)
• Why is ice less dense than water?

  The water molecules in ice are further apart so the hydrogen bonds holding then together are also further apart making it less dense
• What is the strongest type of intermolecular force?

  Hydrogen bonding
• What is the weakest type of intermolecular force?

  Induced dipole-dipole forces