3.2.1 Periodicity

• Periodicity is the repeating pattern/ trends (of physical/ chemical properties/ reactions ) across a period
• Atomic radius

  The atomic radius increases down the group

  The nuclear charge increase as the number of protons increases

  The shielding increases as there are more energy levels

  Therefore electrons are attracted less strongly

  Therefore the atomic radius increases
• 1st ionisation

  The first ionisation energy decreases as you go down groups

  > As you go down a group the atoms get bigger

  > The distance between the nucleus and the outer electron increase

  > The outer electron is more shielded from the nucleus

  > The outer electron is less strongly attracted to the nucleus and more easily removed

  > Therefore less energy is needed to remove the outer election
• First deviation: Period 3

  There is a deviation in the first ionisation energies between Aluminium and Magnesium in Period 3.

  This is because Aluminium’s outer electron is in the 3p orbital and Magnesium’s outer electron is in the 3s orbital.

  The 3p orbital has a higher energy level and therefore less energy is required to remove the electron.

  Therefore Aluminium has a lower first ionisation energy than Magnesium.
• Second deviation: Period 3

  Sulfur's outer electron is easier to remove because it is paired in the 3p orbital so there is electron repulsion , where as phosphorus's outer electron is not paired in an orbital and is harder to remove than a paired electron.
• Metallic bonding Period 3 ( Na, Mg, Al )

  There is a strong electrostatic force of attraction between the positive ions and sea of delocalised electrons, which requires more energy to overcome therefore metals have high m.p/bp
• Comparing melting points

  > Charge and size of the metal ion

  > The number of delocalised electrons

  > Strength of the metallic bond
• Explain why Magnesium has a higher melting point than Sodium

  The Mg2+ is more highly charged and smaller in size compared to Na+

  Magnesium has more delocalised electrons than sodium the force of attraction between Mg2+ and sea of delocalised electrons is stronger than that between the Na+ and sea of delocalised electrons . Therefore more energy is required to overcome the stronger force of attraction
• Silicon

  Type of bonding : Covalent

  Type of structure : Giant covalent structure

  Explanation:

  Silicon has a very high melting point because a lot of energy is required to break many strong covalent bonds
• Phosphorus P4 , sulfur S8 and chlorine Cl2

  Type of bonding : Covalent

  Type of structure : simple molecular

  There are weak Van der Waals forces between the molecules
• Explain why Sulfur(S8) has a higher mp/bp compened to P4?

  Sulfur, S8, is a bigger molecule, it has a larger surface area than phosphorus, P4

  therefore sulfur has more/stranger Van der Waals forces between molecules.

  therefore more energy is required to overcome the stronger forces of attraction
• Argon

  Type of Structure: Monatomic

  Type of bonding: None

  > Atoms are held together by weak Van der Waals forces therefore it has a very low melting/boiling point .