periodicity

• Periodicity

  The repeating pattern of physical or chemical properties going across the periods
• Classification of elements

  • Elements are classified as s, p or d block, according to which orbitals the highest energy electrons are in
• Atomic radius

  Atomic radii decrease from left to right across a period, because the increased number of protons create more positive charge attraction for electrons which are in the same shell with similar shielding
• 1st Ionisation Energy

  There is a general trend across to increase. This is due to increasing number of protons as the electrons are being added to the same shell
• 1st Ionisation Energy

  There is a small drop between Mg + Al. 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
• 1st Ionisation Energy

  There is a small drop between phosphorous 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
• Melting and boiling points

  For Na, Mg, Al- Metallic bonding : 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
• Melting and boiling points

  Si is Macromolecular: many strong covalent bonds between atoms, high energy needed to break covalent bonds– very high mp +bp
• Melting and boiling points

  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
• Melting and boiling points

  S8 has a higher mp than P4 because it has more electrons (S8 =128)(P4=60) so has stronger v der w between molecules
• Melting and boiling points

  Ar is monoatomic weak van der waals between atoms
• Similar trend in 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)