Periodicity

• what is periodicity


  Periodicity is the repeating pattern of physical or chemical properties going across the periods
• what elements does period 2 consist

  Period 2 = Li, Be, B, C, N, O, F, Ne
• what elements does period 3 consist

  Period 3 = Na, Mg, Al, Si, P, S, Cl, Ar
• what is atomic radius

  distance from the nucleus of an atom to the outermost orbital of its electron
• atomic radius trend across period

  Atomic radii decrease from left to right across

  increased number of protons create more positive charge attraction for electrons which are in the same shell
• what is ionisation energy


  the amount of energy required to remove an electron from an atom
• 1st ionisation energy across period

  Across the period trend increase.

  This is due to increasing number of protons as the electrons are being added to the same shell.
• why does the ionisation energy drop between magnesium and aluminium

  Mg has its outer electrons in the 3s sub shell, whereas Al is starting to fill the 3p subshell. Al’s electron is slightly easier to remove because the 3p electrons are higher in energy.
• why is there a small drop between phosphorus and sulfur

  Sulfur’s outer electron is being paired up with an another electron in the same 3p orbital. When the second electron is added to an orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove
• Describe the metallic bonding in Na Mg Al

  strong bonding – gets stronger the more electrons there are in the outer shell that are released to the sea of electrons.

  A smaller sized ion with a greater positive charge also makes the bonding stronger. Higher energy is needed to break bonds
• why is Si macro molecular

  : many strong covalent bonds between atoms, high energy needed to break covalent bonds– very high mp +bp
• why are Cl2 (g), S8 (s), P4 (S)- simple molecular


  weak van der waals between molecules, so little energy is needed to break them – low mp+ bp
• why does S8 have a higher mp + bp than P4

  S8 has a higher mp than P4 because it has more electrons (S8 =128)(P4=60) so has stronger van der waals between molecules
• why does Ar have weak van der waals between atoms

  because it is monoatomic
• draw graph for atomic radius across period 3

  label

  
• melting and boiling point across period 2

  • Li,Be metallic bonding (high mp)
  • B,C macromolecular (very high mp)
  • N2 ,O2 molecular (gases! Low mp as small v der w)
  • Ne monoatomic gas (very low mp)
• draw graph for first ionisation energy across period 3

  label

  
• draw graph for melting and boiling point across period 3

  label