Periodicity

• How are elements classified in the periodic table?


  Elements are classified as s, p, or d block according to which orbitals the highest energy electrons are in.
• What is the trend in atomic radius across a period?

  • Atomic radii decrease from left to right across a period.
  • Increased number of protons creates 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?

  The first ionisation energy 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 magnesium and aluminium?

  Mg has its outer electrons in the 3s subshell, while Al is starting to fill the 3p subshell, making Al's electron slightly 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 that makes it easier to remove.
• What are the melting and boiling points trends for Na, Mg, and Al?

  • Na, Mg, Al exhibit metallic bonding.
  • Stronger bonding occurs with more electrons released to the sea of electrons.
  • Smaller ions with greater positive charge lead to stronger bonding.
  • Higher energy is needed to break these bonds.
• 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 these bonds, resulting in high melting and boiling points.
• How do the melting and boiling points of Cl2, S8, and P4 compare?

  • Cl2 (g), S8 (s), P4 (s) are simple molecular structures.
  • They have weak van der Waals forces, requiring little energy to break.
  • S8 has a higher melting point than P4 due to having more electrons, resulting in stronger van der Waals forces.
• What type of bonding does argon exhibit and what are its melting and boiling points like?

  Argon is monoatomic with weak van der Waals forces between atoms, resulting in low melting and boiling points.
• What is periodicity in the context of the periodic table?

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

  • Similar trends in atomic radius and ionisation energy are observed in both periods.
  • Drops occur between Be & B and N to O for similar reasons.
  • Change 3s and 3p to 2s and 2p in explanations for period 2.
• What types of bonding are present in period 2 elements like Li, Be, B, C, N, O, F, and Ne?

  Li and Be exhibit metallic bonding, B and C are macromolecular, N2 and O2 are molecular gases, and Ne is a monoatomic gas.
• What is the melting point trend for the elements in period 2?

  Li and Be have high melting points due to metallic bonding, B and C have very high melting points due to macromolecular structure, while N2, O2 are gases with low melting points, and Ne has a very low melting point.