Periodicity

• The periodic table arranges elements by proton number

  1. The periodic table is arranged into periods and groups by atomic number.
  2. All the elements within a period have the same number of electron shells
  3. All the elements within a group have the same number of electrons in the outer shell - so they have similar properties
• 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.
• What is the general trend of first ionization energy across a period?


  First ionization energy generally increases across a period.
• Why is there a drop in first ionization 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.
• What causes the drop in first ionization 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?


  • Na, Mg, Al exhibit metallic bonding.
  • Stronger bonding occurs 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 high energy to break, resulting in very 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.
  • Weak van der Waals forces require little energy to break.
  • 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 and exhibits weak van der Waals forces between atoms.
• What is periodicity in chemistry?


  • 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 ionization energy?


  • Similar trends in atomic radius and ionization energy.
  • Drops occur between Be & B and N to O for similar reasons.
  • Change 3s and 3p to 2s and 2p in explanations.
• 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 Li and Be compared to B and C in period 2?


  Li and Be have high melting points due to metallic bonding, while B and C have very high melting points due to macromolecular structures.
• What is the melting point trend for N2, O2, and Ne in period 2?


  N2 and O2 are gases with low melting points, while Ne is a monoatomic gas with a very low melting point.
• 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
• How is the number of outer electrons indicated in the Periodic Table?

  By the group number
• What are the blocks in the Periodic Table based on electron configuration?

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

  Trends within the Periodic Table
• 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 attractive forces
• 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?

  Less nuclear attraction and more shielding
• How are melting points of period 3 elements linked to their structure?

  • Metals (Na, Mg, Al): higher melting points due to metallic bonding
  • 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 charged ions increase bonding strength
• What type of structure does silicon have?

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

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

  Simple covalent molecules
• Why do phosphorus, sulphur, and chlorine have 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