bonding

• Ionic Bonding


  Bonding that occurs between a metal and a non-metal
• Ionic Bonding process


  1. Electrons are transferred from the metal to the non-metal to achieve full outer shells

  2. Charged particles called ions are created

  3. Oppositely charged ions attract through electrostatic forces to form a giant ionic lattice
• Covalent Bonding


  Covalent bonds form between two non-metals. Electrons are shared between the two outer shells in order to achieve a full outer shell. Multiple electron pairs can be shared to produce multiple covalent bonds.
• Covalent bond representation


  Shared electron pairs can be represented using dot and cross diagrams and a covalent bond shown with a straight line.
• Dative bonding


  Dative or coordinate bonds form when both of the electrons in the shared pair are supplied from a single atom. It is indicated using an arrow from the lone electron pair.
• Once a dative bond has formed, it is treated as a standard covalent bond as it reacts in exactly the same way.
• Metallic bonding


  Consists of a lattice of positively charged ions surrounded by a 'sea' of delocalised electrons. This produces a very strong electrostatic force of attraction between these oppositely charged particles.
• The greater the charge on the positive ion


  The stronger the attractive force as more electrons are released into the 'sea'
• Ions that are larger in size, such as Barium


  Produce a weaker attraction due to their greater atomic radius
• Crystal structures


  • Ionic
  • Metallic
  • Simple molecular
  • Macromolecular
• Ionic crystal structure


  Substances have a high melting and boiling point due to the strong electrostatic forces holding the ionic lattice together
• Ionic substances in molten or solution state

  Can conduct electricity as the ions separate and are free to move, carrying a flow of charge
• Ionic substances


  Are often brittle materials as the layers of alternating charges can distort and repel, breaking apart the lattice into fragments
• Metallic structure


  Substances are often good conductors as the 'sea of delocalised electrons' can move and carry a flow of charge
• Metals


  Are malleable as the layers of positive ions can slide over one another, and the delocalised electrons prevent fragmentation
• Metallic substances


  Have high melting points and are nearly always solid at room temperature due to the strong electrostatic forces of attraction
• Simple molecular structure


  Substances consist of covalently bonded molecules held together with weak van der waals forces, a type of intermolecular force
• Van der Waals forces

  Very weak intermolecular forces that require little energy to overcome
• Simple molecular substances have

  Low melting and boiling points
• Water has a simple molecular structure but an unusually high boiling point due to hydrogen bonding
• Simple molecular substances


  • Very poor conductors as their structure contains no charged particles
• Macromolecular substances


  Covalently bonded into a giant lattice structure
• Macromolecular substances


  • Each atom has multiple covalent bonds which are very strong, giving the substance a very high melting point
  • The strength of the covalent lattice makes macromolecular substances rigid
• Macromolecular structure


  • Diamond - made up of carbon atoms each bonded to four further carbon atoms
• Diamond


  • One of the hardest, strongest materials known
• Macromolecular structure


  • Graphite - made up of carbon atoms bonded to three others in flat sheets
• Graphite


  • Electrons not used in bonding are released as free electrons which move between layers, meaning it can conduct electricity
• Molecule shape


  Determined by the number of electron pairs around the central atom
• Electron pairs


  • Naturally repel each other so that the largest bond angle possible exists between the covalent bonds
  • Lone pairs present around the central atom provide additional repulsive forces, reducing the bond angle between covalent bonds by 2.5° for each lone pair
• Determining molecule shape


  1. Find the number of electron pairs

  2. Determine how many are bonding pairs and how many are lone pairs

  3. Bonding pairs indicate the basic shape and lone pairs indicate any additional repulsion
• Molecule shapes


  • Linear (2 bonding pairs, 0 lone pairs, 180° bond angle)
  • Trigonal planar (3 bonding pairs, 0 lone pairs, 120° bond angle)
  • Tetrahedral (4 bonding pairs, 0 lone pairs, 109.5° bond angle)
• Electronegativity


  The power of an atom to attract negative charge towards itself within a covalent bond
• Electronegativity increases along a period as atomic radius decreases and decreases down a group as shielding increases
• Permanent dipole


  Formed when two atoms with different electronegativities are bonded, causing the more electronegative atom to draw more of the negative charge towards itself
• Permanent dipole


  • Hydrogen fluoride - fluorine is more electronegative than hydrogen so electrons are drawn to the right
• Induced dipole


  Can form when the electron orbitals around a molecule are influenced by another charged particle
• Van der Waals forces

  The weakest type of intermolecular force, acting as an induced dipole between molecules
• Van der Waals forces

  • Stronger for larger molecules and straight chain molecules compared to branched chain molecules
• Permanent dipole forces


  Act between molecules with a polar bond, with the + and - regions attracting each other
• Hydrogen bonding


  The strongest type of intermolecular force, forming between hydrogen and the three most electronegative atoms: nitrogen, oxygen and fluorine