Bonding

• Metallic bonding is the electrostatic attraction between positive metal ions and delocalised electrons arranged in a giant metallic lattice
• metallic structures have the following physical properties:

  • High melting and boiling points
  • Strong
  • Good electrical conductor
  • Malleable/ ductile
• Metals are mostly solids at room temperature as lots of energy is required to overcome the strong electrostatic forces of attraction between positive metal ions and delocalised electrons
• Bond strength is higher with

  • smaller ions - greater charge density
  • More highly charged ions - greater charge density and more electrons in the electron cloud
• Across period 3, the melting point increases as it has a higher charge, so it has a greater charge density and therefore more electrons in the electron cloud. They are also a smaller ion so more energy is required to overcome the bonds
• Down a group , the melting point decreases as they are smaller ions so has a greater charge density, but it has the same charge and number of electrons so more energy is needed to overcome the bonds
• Metals can conduct electricity as the delocalised electrons are mobile
• Metals are ductile and malleable as they are made out of layers of ions which can slide over one another while still retaining the same crystal structure
• ionic bonding is the electrostatic attraction between oppositely charged ions arranged in a giant ionic lattice
• Ionic compounds have the following crystal structure:

  • high melting and boiling points
  • hard
  • often soluble in aqueous solution
  • poor electrical conductors when solid but good when molten or dissolved
  • brittle
• Ionic compounds are solids are room temperature and have high melting points as lots of energy is required to overcome the strong electrostatic forces of attraction between positively charged ions
• Bond strength is higher with smaller ions and more highly charged ions
• Ionic compounds cannot conduct electricity when solid as there are no mobile ions
• Ionic compounds are brittle as if the layers move, similarly charged ions will be next to each other which causes repulsion and splits the crystal
• Covalent bond is a shared pair of electrons
• a dative bond is a covalent bond in which both electrons of the shared pair comes from the same atom
• simple molecular have low melting and boiling points and are poor conductors
• simple molecules have low melting points as there are only weak intermolecular forces between the molecules
• Simple molecules have low melting point as little energy is required to break the weak Van Der Waals
• Macromolecular structures have the following physical properties:

  • High melting and boiling points
  • hard and strong
  • insoluble
  • poor electrical conductors (except graphite)
• Macromolecular structures have high melting points are they have many strong covalent bonds between atoms and lots of energy is needed to overcome them
• Graphite can conduct electricity as each carbon atom is covalently bonded to 3 other carbon atoms (bond angle 120) , and the 4th carbon is delocalised so can move around in the structure
• VESPR:

  • Pairs of electrons which surround an atom repel one another
  • Electron pairs become as far apart as possible
  • This determines the shape of simple molecules
  • Lone pairs repel more than bonding pairs ( reducing the angle by around 2.5)
• 2 electron pairs

  Linear, 180
• 3 electron pairs

  Trigonal planar, 120
• 4 electron pairs

  Tetrahedral, 109.5
• 5 electron pairs

  trigonal bi pyramidal, 120 and 90
• 6 electron pairs

  octohedral, 90
• 4 bonding pairs and 2 lone pairs

  Square planar, 90
• 2 bonding pairs and 2 lone pairs

  Non linear, 104.5
• 3 bonding pairs and 2 lone pairs

  Trigonal planar, 120
• 2 bonding pairs and 1 lone pair

  non linear, 117.5
• 3 bonding pairs and 1 lone pair

  trigonal pyramidal, 107
• As you go across the periodic table, electronegativity increases. This is because nuclear charge increases, atomic radius increases and shielding remains the same. There is a strong electrostatic forces of attraction between the nucleus and shared pair of electrons
• Electronegativity is the power of an atom to attract a shared pair of electrons in a covalent bond
• Electronegativity decreases down a group because atomic radius increases, shielding increases, so there is weak electrostatic forces of attraction between the positive nucleus and shared pair of electrons
• Polar covalent bond is when there is a difference In electronegativity. There is an uneven distribution of electrons, which causes the electrons to be pulled closer to the more electronegative atom which creates a dipole and the bond is polar
• If a molecule is symmetrical, the dipoles cancel out and the molecule is non-polar
• Van der Waals forces occur when electron movement in the first molecule leads to an uneven distribution of electrons, creating an instantaneous dipole, which induces a dipole in a neighbouring molecule, and the  δ+ attracts the  δ- in adjacent molecules
• Van der Waals are the only intermolecular force of attraction between non-polar molecules