OCR Chemistry 3 Higher tier

A+ level

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  • Created by: Sophie
  • Created on: 16-04-11 17:47

C3a What are atoms like?

  • Always same no. of protons + neutrons so atoms are neutral
  • Isotopes – same atomic no. but different neutron numbers so different masses

Proton found in the nucleus, relative mass 1, relative charge +1, found by atomic number.

Electron found outside the nucleus, relative mass 0.0005, relative charge -1, found by atomic number.

Neutron found in the nucleus, relative mass 1, relative charge 0, found by mass-atomic number

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C3b How atoms combine – ionic bonding

  •  Salt is used in seasoning, manufacturing pulp/paper, setting dyes in textiles/fabric
  • Ionic compound – joined together by ionic bonding, when the compound is formed, the atoms form +ve (metal) & -ve ions (non-metal)
  • Metal ions have +ve charges, non-metal ions have –ve charges
  • When an atom forms an ion it achieves a stable octet
  • Ionic lattices are held by positive ions which are electrostatically attracted to the –ve ions – a lot of energy is needed to pull ions apart – high m.p.
  • Ionic compounds can’t conduct electricity when solid because electrons can’t flow through them, the strong attraction prevents movement, when molten they can
  • Most ionic compounds attracted to the charges in water so they are soluble, the ions separate and the solution conducts electricity
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C3c Covalent bonding and the structure of the Peri

  • Natural gas = methane (covalent bonding of H & C)
  • Covalent bonding  – 2 non-metals atoms joined to form a molecule
  • Covalent compounds – molecules with different non-metal atoms joined
  • Pair(s) of electrons are shared so all atoms get full outer shells
  • They are really strong and require lots of energy to break them but have weak intermolecular forces, water is unusual with a high m.p’s and b.p’s
  • Covalent molecules are uncharged as there are no ion or free electrons
  • Elements in the same group (periodic table) have similar properties
  • The group(column) no. tells you the no. or electrons on the outer shell
  • The period(row) no. tells you the number of shells

NOTE: The 3 rules above are excluding the transition metals

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C3d The Group 1 elements

  • A flame test can be used to find different metals as they burn with different flames
  • The alkali metals (group 1) all react with water, reactivity increases down the group
  • Adding a lit splint to a gas, tests for hydrogen – makes a squeaky pop if present
  • When they react they lose their lone electron on their outer shell – oxidation
  • Down the group, they lose their electron easier because they have more shells and so the electron is further from the nucleus’ attraction – shielding
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C3e The Group 7 elements

  • The halogens (group 7) have many uses: e.g. chlorine for sterilisation, pesticides and plastics; iodine for wound sterilisation
  • Chlorine is a green gas, bromine is an orangey-red liquid, iodine is a grey solid
  • The alkali metals react with the halogens to form salts called metal halides
  • The reactivity decreases down the group, displacement reactions are used to determine the reactivity, a more reactive halogen displaces a less reactive one
  • Halogens have seven outer electrons and undergo reduction as they gain an electron
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C3f Electrolysis

  • Electrolysis of sulphuric acid is done in a Hofmann voltameter, H2 (cathode) + O2 (anode) are released, the electrodes are made of platinum
  • Half equations - Cathode: 2H+ + 2e- ® H2, Anode: 4OH- ® O2 +2H2O +4e-
  • Aluminium is from the mineral bauxite in the form of aluminium oxide, aluminium is extracted from the purified oxide by electrolysis:  2Al2O3 ® 4Al + 3O2
  • It is dissolved in molten cyrolite because it is insoluble in water and has a high m.p.
  • The electrodes are made of graphite(carbon), the anodes are at the top, the cathode is the lining, the molten aluminium sinks below the electrolyte and is funnelled out
  • Half equations – Cathode: Al3+ + 3e- ® Al, Anode: 2O2- ® O2 + 4e-
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C3g Transition elements

  • Margarine is made by the hydrogenation of vegetable oils (addition of H2)
  • N2 + H2 combine in high pressures and temps. to make ammonia (Haber Process)
  • The transition elements are metals between groups 2-3, they have typical properties – shiny, conductors, high m.p/density/hardness, low reactivity, coloured compounds
  • They are particularly useful when mixed in alloys
  • Transition metal carbonates thermally decompose, its metal oxide and CO2 form
  • Precipitation is a reaction that produced an insoluble solid from two mixed solutions
  • Sodium hydroxide reacts with transition metals to form a coloured metal hydroxide
  • Colour of metal hydroxides- Copper(II): blue, Iron(II): green/grey, Iron(III):orange
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C3h Metal structure and properties

  • Metal properties: high density, lustrous (shiny), high tensile strength, high m.p./b.p., good electricity/heat conductors, hard etc.
  • All metals are made of crystals, in which metal ions are held in a very strong, regular arrangement – metallic bonding - +ve metal ions are surrounded by mobile electrons, electrostatic attraction holds all the delocalised electrons and +ve ions
  • Metals are hard, with high m.p’s/b.p’s because of their strong formation, they conduct electricity as the electrons are free to move in between
  • At very low temps. some metals become superconductors – little or no resistance, so less energy loss, it makes them super fast but are not very practical
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