Chemistry 1.2 Periodic Table

• Atomic number


  Unique to each element, can be considered an element's fingerprint
• The number of electrons changes during chemical reactions, but the atomic number does not change
• Group number


  Indicates the number of electrons in the outer shell (valence electrons)
• This rule holds true for all elements except helium, which has only 2 electrons in its first shell despite being in group 0
• Elements in the same group

  • React similarly
  • By observing the reaction of one element from a group, you can predict how the other elements in that group will react
• The group 1 metals become more reactive as you move down the group while the group 7 metals show a decrease in reactivity moving down the group
• The word 'periodic' is used in the name of the periodic table as similar properties appear in elements placed at regular intervals throughout the table
• Mendeleev's periodic table


  • Organised elements into vertical columns based on their properties and the properties of their compounds
  • Arranged them horizontally in order of increasing atomic mass
  • Left gaps in the table for elements that had not yet been discovered
• When the undiscovered elements were later found, they fit the pattern developed by Mendeleev, confirming his theories
• Isotopes were not known in Mendeleev's time, and he made no provisions for them in his table, leading to some inaccuracies
• Metals


  Elements that react by losing electrons to form positive ions
• Non-metals


  Elements that react by gaining electrons to form negative ions
• Metalloids/semi-metals


  Elements that display properties of both metals and non-metals
• Metallic character of elements

  Decreases as you move across a period from left to right, increases as you move down a group
• Ion


  An atom or molecule which has become charged through the loss or gain of one or more electron(s)
• Cations


  Positive ions
• Anions


  Negative ions
• Atomic structure and position on the periodic table

  • Metals further to the left have fewer electrons to remove from their outer shells, making them more reactive
  • Non-metals on the right have more outer electrons, making it more feasible for them to gain or share electrons
• General properties of metals and non-metals

  • [List of properties]
• Noble gases


  Elements in group 0 of the periodic table, all non-metal, monatomic, colourless, non-flammable gases at room temperature
• Noble gases


  • Have full outer shells of electrons, making them extremely stable and unreactive
  • Except helium, they all have 8 valence electrons
• Uses of noble gases

  • Helium for balloons
  • Neon, argon, xenon in advertising signs
  • Argon for welding and light bulbs
• Trends in physical properties of noble gases

  • Boiling point increases down the group due to increasing atomic mass and intermolecular forces
  • Density increases down the group
• Alkali metals


  Group 1 metals, form alkaline solutions when reacting with water
• Alkali metals


  • Soft metals that can be easily cut
  • Have relatively low densities and low melting points
  • Very reactive, only need to lose one electron to become highly stable
• Trends in properties of alkali metals

  • Get softer as you move down the group
  • Melting points decrease as you move down the group due to decreasing attractive forces between outer electrons and positive ions
• Alkali metals


  Group 1 elements that have one electron in their outermost shell
• Alkali metals


  • Soft metals which can easily be cut with a knife
  • Have relatively low densities and low melting points
  • Very reactive (only need to lose one electron to become highly stable)
• The alkali metals lie on the far left of the periodic table, in the very first group
• Alkali metals


  • Softer as you move down the group
  • Potassium has a lower density than sodium
  • First three alkali metals are less dense than water
  • Melting points decrease as you move down the group due to decreasing attractive forces between outer electrons and positive ions
• As you go down group 1

  The reactivity of the alkali metals increases
• When a group 1 element reacts, its atoms only need to lose one electron, as there is only 1 electron in the outer shell
• When a group 1 atom loses an electron, 1+ ions are formed
• As you go down group 1

  The number of shells of electrons increases by 1
• As the outermost electron gets further away from the nucleus


  There are weaker forces of attraction between the outermost electron and the nucleus
• As the force of attraction gets weaker


  Less energy is required to overcome it, so the outer electron is lost more easily
• The alkali metals get more reactive as you descend the group
• The group 1 metals all have 1 electron in their outer shell
• Reactions of the first three alkali metals with water

  Become more vigorous as you descend the group
• Rubidium, caesium and francium will react even more vigorously with air and water than the first three alkali metals