C2: Periodic Table

• Periodic table


  A table that arranges the elements in order of increasing atomic number, with elements having similar properties placed in the same vertical column (group)
• Development of the periodic table

  1. Early 1800s: Elements arranged by atomic mass

  2. Mendeleev left gaps and predicted new elements

  3. Discovery of isotopes confirmed Mendeleev's approach
• Early periodic tables were not complete and some elements were placed in the wrong order
• Mendeleev's table of elements

  Arranged elements mainly in order of atomic mass but switched order if properties meant they should be changed
• Mendeleev left gaps in the table to make sure elements with similar properties stayed in the same groups, and these gaps indicated the existence of undiscovered elements
• Mendeleev made good predictions about the properties of an undiscovered element he called eka-silicon, which turned out to be germanium
• Modern periodic table

  • Elements are laid out in order of increasing atomic number
  • Elements with similar properties are placed in the same vertical column (group)
  • Elements in the same group have the same number of electrons in their outer shell
• Periods

  Horizontal rows in the periodic table, each representing a new full shell of electrons
• Properties of metals

  • Strong but malleable
  • Good conductors of heat and electricity
  • High boiling and melting points
• Properties of non-metals

  • Dull looking
  • Brittle
  • Not always solids at room temperature
  • Poor conductors of electricity
  • Often have low density
• Transition metals


  • Located in the centre of the periodic table
  • Can have more than one ion
  • Ions are often coloured
  • Make good catalysts
• Group 1 elements (alkali metals)


  • Reactive, soft metals
  • Have low melting and boiling points
  • Form ionic compounds with non-metals
• The further down Group 1 you go, the larger the atoms and the more reactive the elements
• Transition metals


  Can have more than one ion, e.g. copper forms Cu+ and Cu2+ ions, cobalt forms Co2+ and Co3+ ions
• Transition metal ions

  • Often coloured, so compounds containing them are colourful, e.g. potassium chromate (VI) is yellow, potassium (VII) manganate is purple
• Transition metal compounds

  • Often make good catalysts that speed up the rate of a reaction, e.g. nickel catalyst used in hydrogenation of alkenes, iron catalyst used in Haber process for making ammonia
• Group 1 Elements


  Reactive, soft metals
• Group 1 Elements


  • Don't need much energy to lose their one outer electron to form a full outer shell, so they readily form ions
• Reaction of Group 1 metals with water

  Produce hydrogen gas and form alkaline hydroxide compounds that dissolve in water
• The more reactive the Group 1 metal


  The more violent the reaction with water
• The more reactive the Group 1 metal

  The more energy released in the reaction with water
• Reaction of Group 1 metals with chlorine

  Form white metal chloride salts
• As you go down Group 1

  Reactivity increases, so the reaction with chlorine gets more vigorous
• Reaction of Group 1 metals with oxygen


  Form different types of metal oxides depending on the Group 1 metal: lithium forms lithium oxide, sodium forms sodium oxide and sodium peroxide, potassium forms potassium peroxide and potassium superoxide
• Group 1 metals

  • Much more active than transition metals, react more vigorously with water, air or Group 7 elements, are much less dense, strong and hard, and have much lower melting points
• Halogens

  Group 7 elements, all non-metals with coloured vapours
• Halogens


  • Exist as molecules which are pairs of atoms
• As you go down Group 7

  Halogens become less reactive, have higher melting and boiling points, and have higher relative atomic masses
• Halogens forming molecular compounds

  Halogen atoms can share electrons via covalent bonding with other non-metals to achieve a full outer shell, e.g. HCl, PCl3, HF, CCl4
• Halogens forming ionic bonds with metals

  Form 1-long called halides (F-, Cl-, Br-, I-) when they bond with metals, e.g. NaCl, Fe2+Br-
• More reactive halogens


  Can displace less reactive halogens from their salts in aqueous solution, e.g. chlorine can displace bromine and iodine, bromine can displace iodine
• Group 0 Elements

  Inert, colourless gases
• Group 0 Elements

  • Have stable full outer electron shells, so don't need to gain or lose electrons to become more stable, and therefore don't react with much
• Group 0 Elements

  • Exist as monatomic gases, not bonded to each other
• As you move down Group 0

  Boiling points increase due to increasing number of electrons leading to greater intermolecular forces
• Neon is a gas at 25°C, so helium must also be a gas at this temperature as it has a lower boiling point
• Radon has a boiling point of -62°C, krypton has a boiling point of -153°C, so xenon should have a boiling point of around -108°C
• Periodic table

  Elements are arranged in order of atomic (proton) number (smaller number) and so that elements with similar properties are in columns, known as groups

  
• Elements in the same periodic group

  Have the same amount of electrons in their outer shell, which gives them similar chemical properties
• John Newlands

  • Ordered his table in order of atomic weight
  • Realised similar properties occurred every eighth element – 'law of octaves' but broke down after calcium