Chemistry C2.A

Compounds
1. Are formed when atoms of two or more elements are chemically combined
2. Example: CO2 is a compound formed from a chemical reaction between oxygen and carbon
3. Difficult to separate the two elements out again.
Isotopes
1. Defintition
  1. Different atomic forms of the same element which have the same number of protons but have a different number of neutrons
2. Same atomic number but different mass numbers
  1. If they have different atomic numbers they would be different elements altogether
3. Carbon 12 and 14 are popular isotopes
Ionic Bonding
1. Atoms lose or gain electrons to form charged particles (ions).
  1. Which are then strongly attracted to each other because of the opposite charges
2. A shell with just one electron want to get rid of the electron
  1. As then they will become a stable ion
  2. means that they will then become strongly attracted to any ion with the opposite charge
3. A nearly full shell wants to get another electron
  1. Because this then means that they would become stable
    1. This then means that they become a ion and are strongly attracted to opposite charge
      1. They will then latch onto the atom that they gave the electron sodium and chlorine in a classic case.
4. Ionic compounds have a regular lattice structure
  1. very strong electrostatic forces of attraction between oppositely charged ions, in all directions
5. Have similar properties
  1. High melting and boling points
    1. Due to strong attraction between the ions
    2. large amount of energy needed to break the bonds
    3. When melted ions are free to move therefore they'll carry electric current
  2. Dissolve easily in water
Ions and formulas
1. groups 1 & 2 and 6 & 7 are most likely to form ions
  1. Group 1 & 2
    1. Metals, lose electrons to form positive ions
  2. Group 6 & 7
    1. Non- metals, gain electrons to become negative ions
      1. Group 7 are halogens which form ionic compounds with alkali metals
        Where halide ion has a 1- charge
        E.g Na+Cl-
  3. Any of the positive ions can combine with any negative ion to form an ionic compound
2. Only elements from opposite sides of the periodic table will form ionic compunds
  1. Where one becomes a positive ion and other a negative
3. The overall charge of any compound is 0
  1. So negative and positive charges must balance
  2. Can use the charges of individual ions to work out formula for ionic compound
4. Electronic structure of Ions
Covalent Bonding
1. Sharing electrons
  1. Only share electrons in outer shells (higher energy levels)
    1. Both atoms feel they have a full outer shell. Gives them a stable structure of noble gas
2. Each atom has to make enough covalent bonds to fill up its outer shell
3. Simple Molecular Substances
  1. Very strong covalent bonds to form small molecules
  2. Attraction between molecules is weak
    1. Melting and boiling points are very low
      1. Molecules are easily parted from each other
        Intermolecular forces are broken
        Not Covalent bonds
  3. Mostly gases and liquids
  4. not conductors no ions of electrical charge
4. Giant covalent Structures
  1. Similar to giant ionic structures but no charged ions
  2. All atoms bonded by strong covalent bonds
    1. very high melting/boiling points
  3. don't conduct electricity not even when molten (except graphite)
  4. Diamond, graphite (both carbon atoms) and silicon dioxide (silca)
Metallic Structures
1. Metal properties
  1. Giant Structure
  2. Metallic bonds involve deloclaised (free) electrons
    1. Come from the outer shell of every metal atom
    2. Electrons are free to move through structure
      1. makes them good conductors of heat and elctricity
2. Regular structure
  1. Electrostatic attraction strong between negative and positive electrons
3. Have layers of atoms that can slide over each other
  1. Allowing them to be bent and shaped
New materials
1. Smart materials
  1. Behave differently depending on conditions e.g temp
  2. used in glasses frames if you bend them pop them in hot water and they will pop back into remembered shape
  3. Used in dental braces when the mouth gets warm alloy will try and pop back pulling the teeth
2. Nanoparticles
  1. Really tiny particles 1-100 nanometers
  2. Contains roughly a couple hundred atoms
  3. different properties to bulk chemical it is made from
Polymers
1. Forces between molecules determine the properties of Plastics
  1. Strong Covalent bonds hold the atoms together in long chains
    1. But it's bonds between different molecule chains determine properties
  2. Thermosoftening polymers
    1. Weak Forces
      1. Individual tangled chains of polymers
        Held together by weak intermolecular forces
        Chains easy to overcome easy to melt
        When cools polymer hardens into new shape
        Melt and remold as many times as you like
        Free to slide over one another
  3. Thermosetting Polymers
    1. Strong forces
      1. crosslinks of polymer chains
        Strong intermolecular forces
        Holds together in a solid structure
        Doesn't soften when it is heated so can't be remolded
        Strong, hard and rigid
Number of Moles = mass in grams (element or compound) / Relative Formula mass (element or compound)
Chemical Analysis and Instrumental methods
1. Chromatography
  1. Small dot of ink on filter paper, place in beaker with water as the filter paper absorbs the water the ink will seep up the paper
    1. Different ink/ solvent will be in different places and be different colours
2. Machines
  1. Identify different compounds and elements
    1. Advantages
      1. very sensitive- detect tiny amounts of substances
      2. Very fast
      3. Very accurate
3. Gas Chromotography
  1. Separate out a mixture of compunds help you identify subsatnces present
    1. gas used to carry substance through a column packed with solid
      1. Substances travels through different speeds so they seperate
        Time taken to get to reactor can be helped to identify substance
        draws a gas chromatograph.
        number of peaks shows the number of compounds
4. Mass spectrometer (Hodgens uses it)
  1. Connected to gas chromotograph
    1. identify substances by process GC-MS

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Chemistry C2.A

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	Created by Natalie Smith over 10 years ago