Bonding

• What is ionic bonding?


  Strong electrostatic forces of attraction between oppositely charged ions held in a lattice
• Give an example of an ionically bonded substance.


  NaCl (sodium chloride - salt)
• Why do ionically bonded substances have high boiling and melting points?

  It takes lots of energy to break strong electrostatic forces of attraction between oppositely charged ions
• Do ionic compounds conduct electricity? Why?

  Yes, when molten or in solution as the ions are free to move and carry charge
• What is simple molecular covalent bonding?

  Strong covalent bonds between atoms, weak van der Waals forces of attraction between molecules
• Are there any lone electrons in simple covalent bonding?

  No, all are involved in bonding
• Can simple molecular covalent molecules conduct electricity? Why?

  No, all electrons are used in bonding and aren't free to move
• Do simple molecular substances have high or low melting and boiling points? Why?

  Low, due to weak van der Waals forces of attraction between molecules that don't take much energy to overcome
• Describe macromolecular covalent bonding.

  Lattice of many atoms held together by strong covalent bonds
• Do substances with macromolecular covalent bonds have high or low melting and boiling points? Why?

  High, as it takes a lot of energy to overcome many strong covalent bonds
• Do substances with macromolecular covalent bonds conduct electricity?

  Most don't, as all electrons are used in bonding
• Draw and describe the structure of diamond.

  3D tetrahedral structure of C atoms, with each C atom bonded to four others
• Draw and describe the structure of graphite.

  Similar to diamond but each C atom is only bonded to 3 others, forming layers with weak van der Waals forces between them
• Why can graphite conduct electricity?

  One electron from each carbon is delocalised and can carry charge
• Describe and draw metallic bonding.

  Lattice of positive metal ions strongly attracted to a sea of delocalised electrons

  
• Do metallic compounds have high or low boiling and melting points? Why?

  High, as strong forces of attraction exist between positive metal ions and negatively charged sea of delocalised electrons
• Do metallic compounds conduct electricity? Why?

  Yes, as delocalised electrons can move throughout the metal to carry charge
• How does the strength of metallic bonds change across the periodic table? Why?

  It increases due to higher charge on metal ions and more delocalised electrons per ion
• Define electronegativity.


  The ability of an atom to attract the pair of electrons in a covalent bond
• What affects electronegativity? (3 factors)

  Nuclear charge, atomic radius, electron shielding
• What is the most electronegative element?

  Fluorine (4.0 on Pauling’s scale)
• How do you get a nonpolar bond?

  Both bonding elements have the same electronegativities
• When do you get a polar bond?

  When bonding atoms have different electronegativities
• What is the strongest type of inter-molecular force?

  Hydrogen bonding
• What is the weakest type of inter-molecular force?

  van der Waals forces
• How do you get a nonpolar bond?

  Both bonding elements have the same electronegativities.
• When do you get a polar bond?


  Bonding atoms have different electronegativities.
• What is the strongest type of inter-molecular force?

  Hydrogen bonding.
• What is the weakest type of inter-molecular force?

  van der Waals forces.
• Describe van der Waals’ forces of attraction.

  Temporary dipoles are created by the random movement of electrons, inducing a dipole in a neighboring molecule, leading to temporary induced dipole-dipole attraction.
• Are van der Waals forces stronger in smaller or larger molecules?

  Larger molecules have stronger van der Waals forces due to more electrons.
• Describe permanent dipole-dipole attraction.


  Some molecules with polar bonds have permanent dipoles, leading to forces of attraction between those dipoles and neighboring molecules.
• What conditions are needed for hydrogen bonding to occur?

  There must be an O-H, N-H, or F-H bond, and a lone pair of electrons on O, N, or F.
• Why is ice less dense than liquid water?

  In liquid water, hydrogen bonds constantly break and reform, while in ice, hydrogen bonds hold molecules in fixed positions, making them slightly further apart.
• What is a dative/co-ordinate covalent bond and when is it formed?

  A dative/co-ordinate covalent bond is formed when an electron-deficient atom/ion accepts a lone pair of electrons from an atom/ion with a lone pair not used in bonding.
• What does the shape of molecules depend on?

  The shape of molecules depends on the number of electrons in the valence shell of the central atom and the number of these electrons in bonded or lone pairs.
• What does the Electron Pair Repulsion Theory state?

  The Electron Pair Repulsion Theory states that electron pairs will take up positions as far away from each other as possible to minimize repulsive forces between them.
• Which type of electron pair experiences the most repulsion?

  Lone pair-lone pair experiences the most repulsion.
• What is the shape, diagram, and bond angle in a shape with 2 bonded pairs and 0 lone pairs?

  The shape is linear with a bond angle of 180°.
• What is the shape, diagram, and bond angle in a shape with 3 bonded pairs and 0 lone pairs?

  The shape is trigonal planar with a bond angle of 120°.