Periodicity

• What does the Periodic Table arrange elements by?

  Proton number
• What do all elements along a period have in common?

  Same number of electron shells
• What do all elements down a group have in common?

  Same number of outer electrons
• What is indicated by the group number in the Periodic Table?

  Number of outer electrons
• How are elements classified in the Periodic Table?

  • s-block: groups 1 and 2
  • p-block: groups 3 to 0
  • d-block: transition metals
  • f-block: radioactive elements
• What is periodicity in the context of the Periodic Table?

  Study of trends in element properties
• What happens to atomic radius along a period?

  It decreases
• Why does atomic radius decrease along a period?

  Increased nuclear charge pulls electrons closer
• What happens to atomic radius down a group?

  It increases
• Why does atomic radius increase down a group?

  More electron shells increase distance from nucleus
• What is electron shielding?

  Inner shells block nuclear attraction
• What happens to ionisation energy along a period?

  It increases
• Why does ionisation energy increase along a period?

  Outer electrons are held more strongly
• What happens to ionisation energy down a group?

  It decreases
• Why does ionisation energy decrease down a group?

  Increased shielding reduces nuclear attraction
• How are melting points of Period 3 elements linked to their structure?

  • Metals (Na, Mg, Al): Higher melting points due to metallic bonding and increased positive charge.
  • Silicon: Very high melting point due to strong covalent bonds.
  • Non-metals (P, S, Cl): Lower melting points due to weak van der Waals forces.
  • Argon: Very low melting point due to weak forces between individual atoms.
• Why do sodium, magnesium, and aluminium have increasing melting points?

  Greater positive charge increases metallic bonding
• What type of structure does silicon have?

  Macromolecular structure
• Why does silicon have a very high melting point?

  Strong covalent bonds require much energy
• What type of molecules are phosphorus, sulphur, and chlorine?

  Simple covalent molecules
• Why do phosphorus, sulphur, and chlorine have relatively low melting points?

  Weak van der Waals forces require little energy
• What is the state of argon at room temperature?

  Gas
• Why does argon have a very low melting point?

  Weak van der Waals forces between individual atoms
• What makes argon very stable?

  Full outer shell of electrons