Chemistry

• Atom


  Smallest part of an element that can exist
• Dalton's model of the atom


  Atoms as solid spheres that could not be divided into smaller parts
• Plum pudding model of the atom

  Sphere of positive charge with negative electrons embedded in it
• Periodic Table


  A table that organises elements based on their properties
• Development of the Periodic Table

  1. First lists of elements

  2. Mendeleev's Periodic Table

  3. Modern Periodic Table
• Alpha scattering experiment


  • Some alpha particles were deflected by the gold foil - this showed that an atom's mass and positive charge must be concentrated in one small space (the nucleus)
• Nuclear model of the atom

  Dense nucleus with electrons orbiting it
• Mendeleev's Periodic Table


  • Accurately predicted properties of undiscovered elements based on gaps in the table
• How elements are ordered in the Periodic Table

  • By atomic mass (early)
  • By atomic number (modern)
• Niels Bohr's discovery


  Electrons orbit in fixed energy levels (shells)
• There are no gaps in the modern Periodic Table - all elements up to a certain atomic number have been discovered
• James Chadwick's discovery


  Uncharged particle called the neutron
• How elements are grouped in the Periodic Table

  • Not grouped (early)
  • Grouped by chemical properties (Mendeleev)
  • Grouped by number of electrons in outer shells (modern)
• Protons and neutrons are in the nucleus, and the electrons orbit the nucleus in shells
• The Periodic Table has a clear distinction between metals and non-metals in the modern version
• Relative mass of sub-atomic particles

  • Proton: 1
  • Neutron: 1
  • Electron: 0 (very small)
• The Periodic Table had problems in the early versions, with some elements grouped inappropriately
• Relative charge of sub-atomic particles

  • Proton: +1
  • Neutron: 0
  • Electron: -1
• Group 0 elements


  • Noble gases
  • Have full outer shells with 8 electrons
  • Are very unreactive (inert)
  • Boiling points increase down the group
• How to find the number of protons in an atom

  The atomic number on the Periodic Table
• Key terms


  • alkali metals
  • chemical properties
  • displacement
  • groups
  • halogens
  • inert
  • isotopes
  • noble gas
  • organised
  • Periodic Table
  • reactivity
  • undiscovered
  • unreactive
• How to calculate the number of neutrons in an atom

  Mass number - atomic number
• Group 1 elements


  • Alkali metals
  • React with oxygen, chlorine, and water
• Atoms have no overall charge because they have equal numbers of positive protons and negative electrons
• Reactions of Group 1 elements

  1. metal + oxygen ➞ metal oxide

  2. metal + chlorine ➞ metal chloride

  3. metal + water ➞ metal hydroxide + hydrogen
• Number of electrons in the first, second, and third shells

  Up to 2 in the first shell, up to 8 in the second and third shells
• Reactivity of Group 1 elements

  Increases down the group
• Element


  Substance made of one type of atom
• Reason for increasing reactivity of Group 1 elements

  Atoms increase in size, outer electron is further from nucleus, weaker electrostatic attraction, more shielding, easier to lose outer electron
• Compound


  Substance made of more than one type of atom chemically joined together
• Group 7 elements


  • Halogens
  • Non-metals that exist as molecules made up of pairs of atoms
• Mixture


  Two or more substances not chemically combined
• Halogens


  • fluorine (F2)
  • chlorine (Cl2)
  • bromine (Br2)
  • iodine (I2)
• Isotopes


  Atoms of the same element (same number of protons) with different numbers of neutrons
• Melting points of halogens

  Increase down the group
• Physical processes to separate mixtures

  • Filtration
  • Crystallisation
  • Distillation
  • Fractional distillation
  • Chromatography