Periodicity

• Periodicity

  Is the trends across a period in terms of reactivity and physical properties, which are repeated in each row/period
• Atomic radius

  The distance between the outermost electron(s) and nucleus
• atomic radius trend

  Across a period, atomic radius decreases
• Why does atomic radius decrease across a period?

  Because nuclear charge (number of protons) increases and there are the same number of energy levels (similar shielding). Therefore, the outer electrons are pulled closer to the nucleus
• What happens to atomic radius down groups and why?

  It increases due to extra energy levels added for each element down the group
• Why do melting points increase from Na-Al(sodium-aluminium)?

  Metal Ion is more charged, smaller metal ion, and metal ion has more delocalised electrons per atom so there is stronger electrostatic forces of attraction between the positive metal ions and sea of delocalised electrons
• Why does silicon (Si) have the highest melting point in period 3

  because it has a giant covalent lattice structure which has many strong covalent bonds so a lot of energy is needed to overcome these bonds
• Why does sulfur have a higher melting point than phosphorus?

  They both have a simple molecular structure. Sulfur exists as S₈ whereas Phosphorus exists as P₄. S₈ is the larger molecule therefore S8 will have stronger Van der Waals forces between molecules so more energy is needed to break these forces
• Why does phosphorus have a higher melting point than chlorine?

  They both have a simple molecular structure. Phosphorus exists as P₄ whereas chlorine exists as Cl2. P₄ is the larger molecule therefore P₄ will have stronger Van der Waals forces between molecules so more energy is needed to break these forces
• Why does chlorine have a higher melting point than argon?

  Cl2 has a simple molecular structure where Ar is monatomic. Chlorine exists as Cl2 whereas Ar exists as Individual atoms. Cl2 is the larger molecule therefore cl2 will have stronger Van der Waals forces between molecules so more energy is needed to break these forces
• Why does argon have a lower melting point than chlorine ?

  Cl2 has a simple molecular structure where Ar is monatomic. Chlorine exists as Cl2 whereas Ar exists as Individual atoms. Ar is smaller therefore Ar will have weaker Van der Waals forces between atoms so less energy is needed to break these forces
• Why is vanadium classified in the d block?

  Because the highest energy electron is in the d orbital
• Melting point

  The average temperature at which a substance turns from solid to liquid
• Why does electronegativity increase across a period?

  Because shielding stays the same, number of protons increases and distance of outer electron to nucleus decreases (atomic radius decreases). Therefore there are stronger forces of attraction between the nucleus to the bonding pair of electrons in the covalent bond