bonding

• ionic bonding is strong electrostatic forces of attraction between oppositely charges ions held in a lattice
• ionically bonded substances have high mp and bps because it takes lots of energy to break strong electrostatic forces of attraction between oppositely charged ions
• ionic conpounds can conduct electricity when molten/in solution because the ions are free to move and carry charge
• simple molecular covalent bonding is strong covalent bonds between atoms, weak van der Waals forces between molecules
• simple covalent bonds cant conduct electricity because all of the electrons are used in bonding and arent free to move
• simple covalent bonds have low mps and bps because the weak van der Waals forces dont take much energy to overcome
• macromolecular covalent bonding is a lattice of many atoms held together by strong covalent bonds
• substances with macromolecular covalent bonds have high mps and bps because it takes lots of energy to overcome many strong covalent bonds
• diamond is a 3D tetrahedral structure of C atoms with each C atom bonded to 4 others
• graphite is similar to diamond but each C atom is only bonded to 3 others so it is in layers.

  it has weak van der waals forges between layers meaning it can slide over eachother easily -> soft, slippery

  one electron from each carbon is delocalised and can carry charge
• metallic bonding is a lattice of positive metal ions strongly attracted to a sea of delocalised electrons. it is malleable because layers can slide over eachother
• metallic compounds have high mps and bps because there are strong forces of attraction between metal ions and negatively charged sea of electrons
• metallic compounds conduct electricity because delocalised electrons are free to carry charge
• across the periodic table, strength of metallic bonds increases -> higher mp an bp

  higher charge on metal ions

  more delocalised electrons per ion

  stronger force of attraction between them
• electronegativity is


  the ability of an atom to attract the pair of electrons in a covalent bond
• things that affect electronegativity:

  nuclear charge

  atomic radius

  electron shielding
• fluorine is the most electronegative element
• you can get a nonpolar bond if both bonding elements have the same electronegativity
• you can get a polar bond if both bonding atoms have different electronegativity
• the strongest type of intermolecular force is

  hydrogen bonding
• weakest type of intermolecular force is

  van der Waals
• van der waals forces are temporary dipoles created by the random movement of electrons -> induces dipole in neighbouring molecule -> temporary induced dipole-dipole attraction
• van der waals forces are stronger in larger molecules because there are more electrons
• permanent dipole dipole attractions are present in some molecules with polar bonds -> forces of attraction between those dipoles and those of neighbouring molecules
• conditions needed for hydrogen bonding:

  • O-H, N-H or F-H bond, lone pair of electrons on O, N or F because they are highly electronegative, H nucleus is left exposed

  • strong force of attraction between H nucleus and lone pair of electrons on O, N and F
• ice is less dense than liquid water because in liquid water, hydrogen bonds constantly break and reform as molecules move about but in ice the hydrogen bonds hold the molecules in fixed positions so they are slightly further apart
• a dative covalent bond is formed when an electron deficient atom/ion accepts a lone pair of electrons from an atom/ion with a lone pair of electrons
• the shape of molecules depends on the number of electrons in the valence shell of the central atom.

  number of these electrons which are bonded or lone pairs
• the electron repulsion theory states that electron pairs will take up positions as far away from eachother as possible to minimise repulsive forces between them
• lone pair-lone pair = strongest repulsion

  lone pair-bonding pair

  bonding pair-bonding pair = weakest repulsion
• 2 bonded pairs, 0 lone pairs

  linear, 180°
• 3 bonded pairs, 0 lone pairs

  trigonal planar, 120°
• 4 bonded pairs, 0 lone pairs

  tetrahedral, 109.5
• 5 bonded pairs, 0 lone pairs


  trigonal bypyramid

  90° and 120°
• 6 bonded pairs, 0 lone pairs

  octahedral, 90°