Periodicity

• How are elements classified in the periodic table?


  Elements are classified as s, p, or d block based on the orbitals of their highest energy electrons.
• What is the trend in atomic radius across a period?


  • Atomic radii decrease from left to right across a period.
  • Increased protons create more positive charge attraction for electrons.
  • Electrons are in the same shell with similar shielding.
• Why does the first ionisation energy generally increase across a period?


  It increases due to the increasing number of protons as electrons are added to the same shell.
• What is the reason for the small drop in first ionisation energy between Mg and Al?


  Mg has its outer electrons in the 3s subshell, while Al starts filling the 3p subshell, making Al's electron easier to remove.
• Why is there a small drop in first ionisation energy between phosphorus and sulfur?


  Sulfur's outer electron is paired with another electron in the same 3p orbital, causing slight repulsion and making it easier to remove.
• What are the melting and boiling points trends for Na, Mg, and Al?


  • They exhibit strong metallic bonding.
  • Bond strength increases with more outer shell electrons.
  • Smaller ions with greater positive charge lead to stronger bonding.
• What type of bonding does silicon exhibit, and what are its melting and boiling points like?


  Silicon is macromolecular with many strong covalent bonds, requiring very high energy to break, resulting in high melting and boiling points.
• What type of molecular structure do Cl2, S8, and P4 have, and what are their melting and boiling points like?


  • They are simple molecular structures.
  • Weak van der Waals forces between molecules result in low melting and boiling points.
  • S8 has a higher melting point than P4 due to more electrons and stronger van der Waals forces.
• What type of bonding does argon exhibit?


  Argon is monoatomic with weak van der Waals forces between atoms.
• What is periodicity in chemistry?


  • Periodicity is the repeating pattern of physical or chemical properties.
  • It occurs across the periods of the periodic table.
• What are the trends in period 2 compared to period 3 regarding atomic radius and ionization energy?


  • Similar trends in atomic radius and ionization energy.
  • Drops between Be & B and N to O for the same reasons as in period 3.
  • Change 3s and 3p to 2s and 2p in explanations.
• What types of bonding and melting points are observed in period 2 elements?


  • Li, Be: metallic bonding (high melting points).
  • B, C: macromolecular (very high melting points).
  • N2, O2: molecular (gases with low melting points).
  • Ne: monoatomic gas (very low melting point).