T2

• Ionic bonding


  Occurs between a metal and a non-metal, electrons are transferred from the metal to the non-metal to form full outer shells
• Ions


  Charged particles formed when electrons are transferred, oppositely charged ions attract through electrostatic forces to form a giant ionic lattice

  
• Ionic bonding


  • The charge of an ion is related to the strength of the ionic bond that forms, larger ions with greater ionic radius have weaker attraction
• Ionic compound


  • Sodium chloride formed from Na+ and Cl- ions
• Dot and cross diagrams


  Used to represent cations (+ve), anions (-ve) and ionic bonding

  
• Covalent bonding


  Forms between two non-metals, electrons are shared between the two outer shells to form a full outer shell, multiple electron pairs can be shared to produce multiple covalent bonds
• Covalent bonding


  • Chlorine (Cl2), oxygen (O2)

  
• Covalent bond length


  Shorter bonds are stronger as the atoms are held closer together, double and triple bonds are shorter and stronger than single covalent bonds
• Dative bonding


  Forms when both electrons in the shared pair are supplied from a single atom, indicated by an arrow from the lone electron pair
• Dative bonding


  • Ammonia (NH3) forming an ammonium ion (NH4+), Al2Cl6
• Simple covalent substances


  Consist of covalently bonded molecules held together by weak van der Waals forces
• Molecule shape


  Determined by the number of electron pairs around the central atom and the repulsion between them, lone pairs provide additional repulsive forces
• Common molecule shapes


  • Linear
  • V-shaped
  • Trigonal planar
  • Triangular pyramid
  • Tetrahedral
  • Trigonal bipyramidal
  • Octahedral
• Electronegativity


  The power of an atom to attract the electron pair in a covalent bond towards itself, increases along a period and decreases down a group
• Bond polarity


  The negative charge around a covalent bond is not evenly spread, a polar bond results from a large difference in electronegativity between two atoms
• Polar molecules


  Arise when there is an overall difference in polarity across the molecule, due to the arrangement of polar bonds and the geometry of the molecule
• Polar and non-polar molecules

  • CO2 is non-polar, H2O is polar
• Van der Waals forces

  The weakest type of intermolecular force, act as an induced dipole between molecules, stronger for larger molecules and straight chain molecules
• Boiling point of alkanes


  Increases with chain length, decreases with branching
• Permanent dipole


  Occurs when the two atoms in a covalent bond have sufficiently different electronegativities
• Intermolecular force


  The distance over which the force acts, making the intermolecular force stronger
• Boiling Point Trends of Alkanes

  • Van der waals forces act between organic alkane chains
  • As the chain length of the alkane increases, so does the Mr of the molecule, resulting in stronger intermolecular forces between the chains, and so the compound has a higher boiling point
  • Branching of alkane chains weakens van der waal forces between the chains as they are less able to pack tightly together, increasing the distance over which the intermolecular forces act and weakening the attractive forces, therefore branched-chain alkanes have lower boiling points than straight-chain alkanes
• Permanent dipole


  If the two atoms that are bonded have sufficiently different electronegativities, a polar bond forms. The more electronegative atom draws more of the negative charge towards itself and away from the other atom, producing a δ- region and a δ+ region
• Hydrogen Fluoride


  • Hydrogen Fluoride is a polar molecule as fluorine is a lot more electronegative than hydrogen so electrons are drawn towards the fluorine atom
• Hydrogen bonding


  The strongest type of intermolecular force, acting between hydrogen and the three most electronegative atoms: nitrogen, oxygen and fluorine. The lone pair on these atoms form a bond with a δ+ hydrogen atom from another molecule

  
• Hydrogen bonding


  • Molecules held together with hydrogen bonds have much higher melting and boiling points compared to similar-sized molecules without hydrogen bonding
  • Water has an unusually high boiling point for the size of the molecule due to the presence of hydrogen bonds that require a lot of energy to be overcome
  • Hydrogen bonds also result in ice having a much lower density than liquid water as they hold the molecules in a rigid structure with lots of air gaps
  • Alcohols have much higher boiling points than alkanes with a similar Mr value due to the ability of the lone electron pair on the oxygen atom to form hydrogen bonds with a hydrogen on another alcohol molecule

  
• Solvent


  Water is a popular choice of solvent. Its hydrogen bonding capabilities allow it to dissolve some ionic compounds by solvating the individual ions, and to dissolve some alcohols by forming hydrogen bonds with their hydroxyl group. However, both water and alcohols are poor solvents for the dissolving of some polar molecules such as halogenoalkanes that cannot form hydrogen bonds
• Boiling Point Trends of Hydrogen Halides

  Hydrogen fluoride is the only hydrogen halide that forms hydrogen bonds between molecules, giving it the highest boiling point. The boiling point increases as you move down the group past hydrogen fluoride because as the halide increases in size, their number of electrons also increases, resulting in more van der waals forces forming between molecules

  
• Metallic bonding


  Metallic bonding consists of a lattice of positively charged ions surrounded by a 'sea' of delocalised electrons. There are very strong electrostatic forces of attraction between these oppositely charged particles. The greater the charge on the positive ion, the stronger the attractive force. Ions that are larger in size, such as barium, produce a weaker attraction due to their greater atomic radius
• Crystal structures


  • Ionic substances have a high melting and boiling point, can conduct electricity when molten or dissolved, and are often brittle
  • Metallic substances are often good conductors, malleable, and have high melting points
  • Simple molecular substances have low melting and boiling points, and are very poor conductors
  • Macromolecular covalent substances have very high melting points due to the strong covalent bonds, and can conduct electricity if they have delocalised electrons
• Diamond


  • Diamond is a macromolecular structure made up of carbon atoms each bonded to four other carbon atoms, forming a rigid tetrahedral structure, making it one of the hardest, strongest materials known
• Graphite


  • Graphite is a macromolecular structure made up of carbon atoms, each bonded to three others in flat hexagonal sheets, with one delocalised electron per carbon atom allowing it to conduct electricity and be used in an electrode. The intermolecular forces between layers of graphite are weak, allowing the layers to easily slide over each other, making graphite a useful lubricant
• Graphene


  • Graphene consists of single, 2D sheets of graphite that are just one atom thick, formed of hexagonal carbon rings, creating a very strong, rigid and lightweight material that can conduct electricity