chemistry structure and bonding

• What are ions

  Charged particles. Can be single atoms or groups of atoms. Metal atoms form positive ions, cations. Non-metal atoms form negative ions, anions.
• Why are ions formed

  Atoms lose or gain electrons to form ions in order to gain a full outer shell like noble gases.
• What is ionic bonding

  When metals react with non-metals, electrons are transferred from the metal to become positively charged ions with a full outer shell of electrons. The non-metal atoms gain electrons and become negatively charged ions with a full outer shell. The oppositely charged ions are strongly attracted to each other and this strong electrostatic attractions holds the ions together in the ionic compound. This is ionic bonding.
• Structure of ionic compound

  Giant ionic lattice which is a closely-packed regular arrangement. Staring electrostatic forces of attraction between oppositely charged ions which act in all directions.

  
• Different ways ionic compounds can be represented

  Dot and Cross, 3D models, Ball and stick

  
  

  1) show how compounds formed

  
  

  2) show relative sizes of ions, regular pattern in an ionic crystal, see outer layer of compound

  
  

  3) regular pattern, how ions are arranged, suggests that the crystal extends beyond what is shown in the diagram. They may show the relative sizes of the ions, but sometimes not shown to scale. Another disadvantage is that they suggest that there are gaps between the ions when there isn't.
• Working out the empirical formula of an ionic compound

  From Dot and Cross - count how many atoms of each element - e.g CaCl2

  
  

  From a 3D model or ball and stick - use diagram to work out what ions are in the ionic compound. Balance the charges of ions until the overall charge on the compound is 0
• Properties of ionic compounds

  Melting and Boiling Point - high MP due to strong electrostatic attraction between the ions. Takes a large amount of energy to overcome and break the bonds.

  
  

  Solubility- most ionic compounds easily dissolve in water

  
  

  Electrical conductivity- does not conduct when solid as all ions are held in fixed positions. Conducts when melted or dissolved as the ions are free to move and carry the electric current.
• What is covalent bonding?

  A covalent bond is formed when a pair of electrons are shared between two atoms. Only share in outer shells. The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forced making the covalent bonds very strong. Occurs between non-metals. Elements of compounds.
• Representing covenant bonding

  Dot and cross, displayed formualas, 3D models and ball and stick

  
  

  1) can represent double covalent bonds, useful for showing which atoms in the bond come from but don't show relative sizes or how they're arranged in space

  
  

  2) covalent bonds as single or double lines, shows how atoms are connected in large molecules, doesn't show 3D structure of the molecule or where the atoms came from

  
  

  3) 3D shoes atoms and arrangement. Balls and stick shows the bonds. 3D models can quickly get confusing, don't know where the electrons in the bond have come from
• Molecular formulas

  How many atoms of each element in diagram
• Simple molecules

  Made up of only a few atoms joined together by covalent bonds
• Examples of simple molecular substances

  Hydrogen, chlorine, hydrogen chloride, methane, ammonia, water, nitrogen and oxygen
• Properties of simple molecules

  Electrical conductivity - does not conduct, no ions or free electrons to carry the charge

  
  

  Melting and Boiling Points - low MP/BP as the intermolecular forced are very weak, must be overcome to melt or boil

  
• Molecular formula for a polymer

  Write down the molecular formulas of the repeating unit by counting the number of atoms of each element it contains, put brackets around it and put an 'n' after the brackets

  
  

  E.g - poly(ethene) (C2H4)nm
• melting and boiling points of polymers

  Polymers have higher MPs and BPs than simple covalent molecules. This is because the intermolecular forces between the larger polymer molecules are stronger, so more energy is needed to break them. This means most polymers are solid at room temperature. The intermolecular forces are
• Giant covalent structures (macromolecules)

  Lattice, all atoms bonded to each other by strong covalent bonds. E.g diamond or graphite. The bonds require a lot of energy to break so very high MP and BP
• List 4 facts abound diamond and what structure it is

  It is a Giant Covalent Structure

  -only made of carbon atoms

  -each atom is bonded to 4 other carbon atoms

  -every bond is covalent and very strong

  -therefore a huge amount of energy is required to break these bonds

  -therefore high MP and BP

  -does not conduct electricity, no free electrons or ions

  
• What are the properties of diamond?

  -has a very high melting and boiling point due to the many strong covalent bonds between every carbon atom

  -this also makes them very hard

  -diamond does not conduct electricity as there are no free electrons to carry the charge
• List 4 facts about graphite and what kind of structure it is

  Giant covalent structure, each carbon atom forms three covalent bonds out of its 4. Sheets of carbon atoms arranged in hexagons. Weak intermolecular forces between layers so free to move over each other. This makes graphite soft and slippery, good lubricant. Had a high MP because the covalent bonds are guard to break and need a lot of energy. Each carbon atoms had one electrons that's delocalised and can move. Graphite conducts electricity and thermal energy.

  
• List 5 facts about Silicon Dioxide and what kind of structure it is

  it is a Giant Covalent Structure

  -has a similar structure to diamond but is made of silicon and oxygen atoms rather than carbon

  -has a high melting and boiling point

  -it is hard and has strong covalent bonds between all atoms

  -each silicon atom is bonded to 4 other oxygen atoms

  -it does not conduct electricity

  
• What is Graphene?

  It is one layer of Graphite, single sheet of carbon atoms joined together in hexagons. One atom thick, a two dimensional compound. The network of covalent bonds makes graphene very strong, it's also light so can be added to composite materials to improve their strength without adding much weight. Like graphite, it contains delocalised electrons so can conduct electricity though the whole structure. Has potential to be used in electronics.

  
• What is the structure of a Simple Covalent Molecule like?

  - there are strong covalent bonds that do not break

  -there are weak intermolecular forces of attraction which need little energy to break

  -when warmed the intermolecular forces are broken

  -individual molecules are held fairly close together by weak forces of attraction

  
• What are the properties of a Simple Covalent Molecule?

  -has a low Melting and Boiling point

  -little energy required to overcome the weak intermolecular forces so it is easily separated into a gas

  -does not conduct electricity as they have no free delocalised electrons to carry the charge

  -soluble in water
• Fullerenes

  Hollow molecules or carbon, shaped like tubes or balls. Mainly made up of carbon atoms arranged in hexagons but can also contain pentagons or heptagons.

  
  

  Buckministerfullerene was the first fullerene to be discovered. Molecular formula is C60 and forms as hollow sphere containing 20 hexagons and 12 pentagons.

  
  

  Nanotubes are fullerene which are tiny carbon cylinders. The ratio between length and diameter of nanotubes is very high and they're good conductors of heat and electricity.
• Uses of fullerenes

  In medicine - used to cage their molecules, fullerenes structure forms around another atom or molecule trapping to inside, could be used to deliver drugs to where it is needed in the body in a highly controlled way.

  
  

  Catalyst - huge surface area, individual catalyst molecules could be attached to the fullerenes.

  
  

  Lubricant - coating moving machine parts in fullerenes reduces friction, one day used for artificial joints

  
  

  Strengthening materials - nanotubes have high tensile strength (they don't break when stretched) so can be used to strengthen materials without adding much weight such as in tennis racket frames

  
  

  Electronics - nanotubes can conduct electricity and they're very small so they can be used in very small electrical circuits for example in the microchips found in computers and phones.
• Structure of metals

  Giant structure, atoms arranged Ina regular pattern, metals said to have giant structures because they have lots of atoms so how many depends on how big the piece of metal is.

  
• what are the 4 key states?

  Solid, liquid, aqueous and gas
• Properties of metals

  High MP and BP - electrostatic forces between the metal atoms and the delocalised sea of electrons are very strong so need lots of energy to break. This means most compounds wth metallic bonds have a very high melting point and no so they're generally sold at room temp.

  
  

  Conductivity - metals have delocalised electrons that are free to move through the whole structure. Because if this, they are good conductors of thermal energy and electricity. The electrons carry the current or the thermal energy though the structure.
• Malleability

  Metals consists of atoms helps together in a regular structure. The atoms form layers that are able to slide over each other. This means they are malleable and clan be net

  
• Alloys

  A mixture of two or more metals and another element, harder and more useful than pure metals.

  
  

  93 - pure gold mixed with copper/'d silver ->
• States of matter

  Depends on how strong the forces of attraction are between the particles of the material, strength of forces between particles is determined by the material (structure, substance, bond type), the temperature and the pressure
• Solids

  Strong forces of attraction between particles, these forces hold the particles close together in fixed positions to form a very regular lattice arrangement. The particles don't move from their positions so all solids keep a definite shape and volume and don't flow like liquids, the particles vibrate about their positions and as the temperature increases, The particles vibrate more. This is why solids expand slightly when heated.

  
• Liquids

  Weak forces of attraction between the particles, randomly arranged and free to move last each other but tend to stick closely together, has a definite volume but don't keep a definite shape and will flow to fill the bottom of a container. The particles are constantly moving with a random motion, the hotter the liquid gets, the faster the particles move. This causes liquids to expand slightly when heated.

  
• Gases

  Forces of attraction between the particles very weak, free to live and do so constantly with random motion. They travel in straight lines until they collide with another particle or with the walls of the container. The particles are very far apart so much so that lost of a gas is empty space. Don't keep definite shape or volume and will always fill any container. The hotter a gas gets, the faster the particles move and the harder and more frequently they hit the walls of the container. This causes the pressure of the gas to increase or if this container isn't sealed, the volume of gas will increase.
• Limitations of particle theory

  Particle theory is a great model for explaining solids, liquids and gases but it isn't perfect. In reality, particles aren't solid, inelastic or spheres, they're atoms, ions and molecules. The model doesn't show the forces between the particles so there's no way of knowing how strong they are. The size of particles and the distances aren't necessarily shown to scale.
• Atomic properties and bulk properties

  Bulk properties - density, MP will stay the same regardless of how many atoms or molecules in a sample. These properties depend on how the particles interact with each their so a single atom or molecule would be have differently
• Changing state

  Only the arrangement or the energy of particles changes
• Melting

  S to L, solid vibrates from energy gain from heat, forces weaken, MP, particles have enough energy to break free from positions
• Boiling

  L to G, particles move faster from energy gain from heat, weakens attractive forces, BP, particles have enough energy to overcome forces between them
• Condensing

  G to L, gas cools, no longer has energy to overcome forces of attraction,