C2 Bonding, Structure and Properties of Matter

• Describe in terms of electron transfer, how sodium (Na) and chlorine (Cl) react to form sodium chloride (NaCl) (3)

  Each Sodium atom loses an electron to form an Na + ion. Each Chlorine atom gains an electron to form a Cl - ion. The oppositely charged ions are attracted to eachother by electrostatic attraction.
• Explain why simple ions often have noble gas electronic structures (2)


  Noble gas electronic structures have a full outer shell, so have a very stable structure.
• Compounds


  Substances in which 2 or more elements are chemically combined
• Types of strong chemical bonds

  • Ionic
  • Covalent
  • Metallic
• Ionic bonding


  • Particles are oppositely charged ions
  • Occurs in compounds formed from metals combined with non-metals
• Covalent bonding


  • Particles are atoms which share pairs of electrons
  • Occurs in most non-metallic elements and in compounds of non-metals
• Metallic bonding


  • Particles are atoms which share delocalised electrons
  • Occurs in metallic elements and alloys
• Formation of ionic bond

  1. Metal atom loses electrons to become positively charged ion

  2. Non-metal atom gains electrons to become negatively charged ion
• An ion is an atom that has lost or gained electron(s)
• Ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 gain full outer shell of electrons, so they have the same electronic structure as a noble gas (Group 0 element)

  
• Ionic compounds


  • Giant structure of ions
  • Held together by strong electrostatic forces of attraction between oppositely charged ions
  • Forces act in every direction since the structure is in 3D
• Covalent bonding


  • Atoms share one or more pairs of electrons
• Polymers


  Large covalently bonded molecules
• Giant covalent structures (macromolecules)

  • Consist of many atoms covalently bonded in a lattice structure
  • Examples: diamond, silicon dioxide
• Diagrams to show covalent substances could be dot and cross, shown as repeat units for polymers using a single line to represent a single bond, ball and stick and two- and three-dimensional diagrams
• Metallic bonding


  • Positive ions (atoms that have lost electron(s)) and delocalised electrons arranged in a regular pattern
  • Delocalised electrons are free to move through the structure
  • Delocalised electrons are shared through the structure so metallic bonds are strong

  
• Metal Atom


  Loses electrons to form a positively charged cation
• Ionic Bond


  A chemical bond between two oppositely charged ions
• Non-metal Atom


  Gains electrons to form a negatively charged anion
• Formation of Ionic Bond

  Attraction between oppositely charged ions
• Simple Molecular Substances

  1. Strong Covalent bonds between the atoms of each molecule
  2. Weak intermolecular forces between molecules
  3. Low melting and boiling points (gaseous at room temperature)
  4. Cannot conduct electricity
• Giant Covalent structures

  1. Every atom Is connected by strong covalent bonds
  2. No weak intermolecular forces as there is only one structure
  3. High melting and boiling points
  4. Cannot conduct electricity (except graphite)
• Predict, with reasoning, whether diamond or poly(ethene) has a higher melting point (3)

  To melt diamond you have to break the covalent bonds between atoms which are very strong, but to melt poly(ethene) you only have to break the weaker intermolecular forces which needs less energy. So diamond has a higher melting point
• Use the diagram to find the empirical formula of the compound (3)

  Caesium is in Group 1 so form 1+ ions, and chlorine is in Group 7 so form 1- ions. Charges balance with one of each ion so empirical formula is CsCl

  
• Diamond

  1. Diamond has a giant covalent structure, made up of carbon atoms that each form four covalent bonds. Makes diamond really hard
  2. Strong covalent bonds take a lot of energy to break - gives diamond a very high melting point
  3. Doesn’t conduct electricity because it has no free electrons or ions.
• Graphite

  1. Each carbon atom only forms three covalent bonds, creating sheets of carbon atoms arranged in hexagons
  2. Aren’t any covalent bonds between the layers - only held together weakly, so they’re free to move over each other. Makes graphite soft and slippery (Lubricating material)
  3. High melting point - needs loads of energy to break the covalent bonds
  4. Only three out of each carbon’s four outer electrons are used in bonds, so each carbon atom has one electron that’s delocalised and can move - Graphite conducts electricity and thermal energy.
• Graphene

  1. Graphene is a sheet of carbon atoms joined together in hexagons - Just one atom thick, making it a 2D compound
  2. Network of covalent bonds make it very strong. Also incredibly light, so can be added to composite materials to improve strength without adding much weight
  3. Contains delocalised electrons so can conduct electricity through the whole structure - potential to be used in electronics
• Fullerenes

  1. Fullerenes are molecules of carbon, shaped like closed tubes or hollow balls
  2. Mainly made up of carbon atoms arranged in hexagons, but can also contain pentagons or heptagons
  3. The fullerene structure forms around another atom or molecule, which is then trapped inside - Could be used to deliver a drug in the body
  4. Have a huge surface area - makes it great industrial catalysts
  5. Also make great lubricants
• Fullerenes can form nanotubes - tiny carbon cylinders. Nanotubes can conduct both electricity and thermal energy. Also have a high tensile strength (dont break when stretched). Technology that uses very small particles such as nanotubes is called nanotechnology. Used in electronics or to strengthen materials without adding much weight
• Give three uses of fullerenes

  Lubricants, catalysts, strengthen materials, deliver drugs to body
• Ionic bonding


  Electrostatic attraction between positive and negative ions. It is a relatively strong attraction.
• How ionic compounds are held together

  1. They are held together in a giant lattice

  2. It's a regular structure that extends in all directions in a substance

  3. Electrostatic attraction between positive and negative ions holds the structure together
• Properties of ionic substances

  • High melting and boiling point (strong electrostatic forces between oppositely charged ions)
  • Do not conduct electricity when solid (ions in fixed positions)
  • Conduct when molten or dissolved in water - ions are free to move
• Ionic compounds are electrically neutral, i.e. positive and negative charges balance each other
• How ionic compounds are formed (using MgO as an example)

  1. Reaction of a metal with a non-metal

  2. Electron transfer occurs - metal gives away its outer shell electrons to non-metal

  3. Mg is in Group II, so has 2 available outer shell electrons

  4. O is in Group VI, so can accept 2 electrons to get a full outer shell configuration

  5. Mg becomes Mg2+ and O becomes O2− (oxide)
• Covalent bond


  Shared pair of electrons between two atoms
• Properties of simple molecular covalent substances

  • Do not conduct electricity (no ions)
  • Small molecules
  • Weak intermolecular forces, therefore low melting and boiling points
• As the mass/size of the molecule increases

  Intermolecular forces increase, causing melting/boiling points to increase as well
• Polymers


  Very large molecules (>100s, 1000s of atoms) with atoms linked by covalent bonds
• Thermosoftening polymers


  Special type of polymers; they melt/soften when heated. There are no bonds between polymer chains. Strong intermolecular forces ensure that the structure is solid at room temperature. These forces are overcome with heating - polymer melts.