Periodic Table of Elements

• An element is a substance that is made up of one type of atom. It cannot be broken down into anything simpler by chemical means.
• Metals have high melting points, are ductile, malleable, sonorous - make a ringing sound when struck and good conductors of heat and electricity

  Non-metals have low melting points(except for diamond and graphite), are not ductile, malleable(will crack/crumble if hit by a hammer) or sonorous, and poor conductors of heat and electricity(except for graphite and graphene)
• Dmitri Mendeleev arranged the elements in order of increasing atomic mass, but also took into account patterns and behaviour of the elements - he reversed the positions of Te and I so as iodine was placed in the same group has chlorine and bromine as it had similar chemistry to those elements

  He found it was necessary to leave gaps in the table and said that these were for elements not known at the time

  His table enabled him to predict the properties of undiscovered elements

  His work was proved correct by the accurate prediction of the properties of gallium and germanium
• A modification to the periodic table was made following the work of Rutherford and Mosely. It was realised that the elements should be arranged in order of increasing atomic number. i.e. the number of protons in the nucleus

  A family of unreactive elements, called group 0 has been discovered and inserted.

  The transition metals have been taken out and placed in a block of elements between group 2 and group 3

  Actinides and Lanthanides are present, a block of elements at the bottom of the periodic table.
• Noble gases are unreactive because they have a full valence shell, and thus do not need to lose or gain electrons to be stable, since the already are.
• The number of electrons in the outermost shell of an element is always the same as the group number
• The size of the atom decreases going across a period, but increases going down a group
• Alkali metals are stored under oil to minimise contact with air and water
• Physical properties of alkaline metals:

  • Soft - can be cut with a knife
  • Low melting and boiling points
  • Shiny when freshly cut but tarnish in the air as the metal oxide forms
  • low density - less than 1g/cm^3
• Safety precautions taken before potassium is added to water:

  • Use a large tub of water
  • Cut a very small piece of metal
  • Use a safety screen
  • Use of tongs/tweezer to hold the metal
• Acid + metal = salt + hydrogen
• Acid + base = salt + water
• Acid + metal carbonate = salt + water + carbon dioxide
• The trend in reactivity for elements in group 1 is that the elements become more vigorous as you go down the group
• The trend for reactivity in halogens is that it gets less reactive going down the group
• Monatomic means consisting of one atom
• Most transition metal compounds are coloured, such as:

  • Copper(II) carbonate - Green powder
  • Copper(II) oxide - Black powder
  • Hydrated copper(II) sulfate - Blue solution
• Differences between group 1 and transition metals

  • Melting point - (Group 1: Low; Transition: High)
  • Density - (Group 1: Low - Li, Na and K are all less dense than water; Transition: High)
  • Reactivity with water - (Group 1: Very reactive with cold water forming metal hydroxide + hydrogen; Transition: Low reactivity with water. Some react with steam to form metal oxide and hydrogen, Cu does not even react with steam)
  • Colour of compounds - (Group 1: White compound; Transition metals: coloured compounds)