C1 Atomic Structure and C2 Periodic Table

• Periodic Table

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

  1. Mendeleev was able to accurately predict the properties of undiscovered elements based on the gaps in the table

  2. The Periodic Table has changed over time as scientists have organised it differently
• Early lists of elements

  • Mendeleev's Periodic Table
  • Modern Periodic Table
• Ordering of elements

  • By atomic weight
  • By atomic number
• Group 1 elements (alkali metals)

  • React with oxygen, chlorine, and water
  • Reactive with water to form an alkali (a solution of their metal hydroxide)
• Lithium + oxygen → lithium oxide

  Lithium + chlorine → lithium chloride

  Lithium + water → lithium hydroxide + hydrogen
• Alkali metals

  Group 1 elements that react with water to form an alkali
• Group 0 elements (noble gases)

  • Have full outer shells with eight electrons, so do not need to lose or gain electrons
  • Are very unreactive (inert) so exist as single atoms as they do not bond
  • Have boiling points that increase down the group
• Group 1 reactivity

  • Increases down the group because the atoms increase in size, the outer electron is further away from the nucleus, and there are more shells shielding the outer electron from the nucleus, so the electrostatic attraction between the nucleus and the outer electron is weaker, making it easier to lose the one outer electron
  • Melting point and boiling point decreases down Group 1
• Group 7 elements (halogens)

  • Non-metals that exist as molecules made up of pairs of atoms
  • Reactivity decreases down the group because the atoms increase in size, the outer shell is further away from the nucleus, and there are more shells between the nucleus and the outer shell, so the electrostatic attraction from the nucleus to the outer shell is weaker, making it harder to gain one electron to fill the outer shell
• Halogens

  Group 7 elements that are non-metals
• Halogens

  • Fluorine (F₁)
  • Chlorine (Cl₂)
  • Bromine (Br₂)
  • Iodine (I₂)
• Melting point and boiling point of halogens

  Increase down the group
• Reactivity of halogens

  Decreases down the group
• Displacement reaction

  When a more reactive element takes the place of a less reactive one in a compound
• Fluorine displaces chlorine as it is more reactive: fluorine + potassium chloride → potassium fluoride + chlorine
• Melting point of noble gases

  Increase down the group
• 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
• 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
• Niels Bohr's discovery

  Electrons orbit in fixed energy levels (shells)
• James Chadwick's discovery

  Uncharged particle called the neutron
• Relative mass of sub-atomic particles

  • Proton: 1
  • Neutron: 1
  • Electron: 0 (very small)
• Relative charge of sub-atomic particles

  • Proton: +1
  • Neutron: 0
  • Electron: -1
• How to calculate the number of neutrons in an atom

  Mass number - atomic number
• Atoms have no overall charge because they have equal numbers of positive protons and negative electrons
• Element

  Substance made of one type of atom
• Compound

  Substance made of more than one type of atom chemically joined together
• Mixture

  Two or more substances not chemically combined
• Isotopes

  Atoms of the same element (same number of protons) with different numbers of neutrons
• Physical processes to separate mixtures

  • Filtration
  • Crystallisation
  • Distillation
  • Fractional distillation
  • Chromatography
• Relative mass


  The average mass of all the atoms of an element
• Method for filtration

  A circle of filter paper is folded to make a cone and placed into a filter funnel . This allows the filtrate (liquid) to pass through the filter paper and the residue (solid) to be left on the filter paper.
• Method for chromatography

  Place the sheet of paper in a beaker with a shallow layer of a solvent . Make sure the level of the solvent is below the pencil line. Place a lid on the beaker and leave the solvent to travel up the paper, carrying the components of the mixture with it
• Method for crystallisation

  1. A solution is placed in an evaporating basin and heated with a Bunsen burner.
  2. The volume of the solution has decreased because some of the water has evaporated. Solid particles begin to form in the basin
  3. All the water has evaporated, leaving solid crystals behind.