2.01 Periodicity

• How are elements in the periodic table arranged?

  Elements are arranged according to their proton number
• What is a period on the periodic table?

  The horizontal rows
• What is a group on the periodic table?

  The vertical columns
• What does the group number indicate on the periodic table?

  The number of outer electrons of an element
• What are the 4 blocks of the periodic table?

  • s-block
  • p-block
  • d-block
  • f-block
• What elements are in each block of the periodic table?

  • s-block = groups 1 and 2
  • p-block = groups 3 to 8
  • d-block = transition metals
  • f-block = radioactive elements
• Define periodicity.

  The study of trends within the periodic table.

  • Often these trends are linked to an element's electronic configurations
• What is the trend in atomic radius along a period?

  Atomic radius decreases
• Why does atomic radius decrease along a period?

  Atomic radius decreases due to an increased nuclear charge for the same number of electron shells/where shielding stays the same

  • This means that the outer electrons are pulled in closer to the nucleus because the charge produces a greater attraction
  • As a result, atomic radius is decreased
• What is the trend in atomic radius going down a group?

  Atomic radius increases
• Why does atomic radius increase down the group?

  • With each increment down a group, an electron shell is added
  • This increases the distance between the outer electrons and the nucleus, reducing strength of attraction
  • More shells also increases shielding, whereby inner shells create a barrier that blocks attractive forces
  • Nuclear attraction is reduced further and atomic radius increases
• What is the trend in ionisation energy along a period?

  Along a period, ionisation energy increases
• Why does ionisation energy increase along a period?

  • Increases because atomic radius decreases, hence nuclear charge increases
  • This means that the outer electrons are held more strongly so more energy is required to remove the outer electron and ionise the atom
• What is the trend in ionisation energy going down a group?

  Going down a group, ionisation energy decreases
• Why does ionisation energy decrease down a group?

  Nuclear attraction between the nucleus and outer electrons reduces, and shielding increases.

  • Both of these factors mean less energy is required to remove the outer electron
• What does the melting point of period 3 elements depend on?

  • Structure of the element
  • Bond strength
• What happens to the melting points across period 3 between sodium and aluminium?

  • These 3 elements are metals with metallic bonding - their melting points increase due to greater positive charge of their ions (Na=1+, Mg=2+, Al=3+)
  • This means more electrons are released in the form of free electrons
  • This increases the electrostatic forces from Na to Al, therefore more energy is required to break them
• Why does the melting point increase dramatically for silicon in period 3?

  Silicon has a very strong giant covalent structure.

  • So more energy is required to break the strong covalent bonds, giving it a very high melting poitn
• Why does the melting point decrease in period 3 between phosphorus and chlorine?

  • Phosphorus, sulfur and chlorine are all simple covalent molecules held with weak VDW forces
  • Less energy is needed to overcome these weak intermolecular forces, so these molecules have relatively low melting points
• Why does argon have an even lower melting point than chlorine?

  Argon is a noble gas which exists as individual atoms with a full outer shell of electrons.

  • This makes the atom very stable, and makes the VDW forces between them very weak
  • As a result, less energy is needed to overcome these weak VDW forces and so argon exists as a gas at room temperature