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
• Blocks of elements

  • s block
  • p block
  • d block
• Atomic radius across a period

  Decreases from left to right
• Reason for decreasing atomic radius

  Increased number of protons create more positive charge attraction for electrons which are in the same shell with similar shielding
• 1st ionisation energy across a period

  Generally increases
• Reason for increasing 1st ionisation energy

  Increasing number of protons as the electrons are being added to the same shell
• 1st ionisation energy between Mg and Al

  Small drop
• Reason for drop in 1st ionisation energy between Mg and 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 between P and S

  Small drop
• Reason for drop in 1st ionisation energy between P and S

  Sulfur's outer electron is being paired up with 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 of Na, Mg, Al

  Increase
• Reason for increasing melting and boiling points of 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 point of Si

  Very high
• Reason for very high melting and boiling point of Si

  Macromolecular: many strong covalent bonds between atoms, high energy needed to break covalent bonds
• Melting and boiling points of Cl2, S8, P4

  Low
• Reason for low melting and boiling points of Cl2, S8, P4

  Simple molecular: weak van der waals between molecules, so little energy is needed to break them