Periodicity

• What is the atomic number range of elements in the periodic table?

  1 to 118
• How are elements arranged in the periodic table?

  By increasing atomic number and similar properties
• What are the outer electrons called?

  Valence electrons
• What is a period in the periodic table?

  A row of elements with the same shell number
• What is a group in the periodic table?

  A column of elements with similar configurations
• Why do H and He not fit comfortably into any group?

  They have unusual electronic configurations
• In which group is helium placed?

  Group 0
• What are the four main blocks of the periodic table?

  s-block, p-block, d-block, f-block
• What defines s-block elements?

  Only s electrons in the outer shell
• What defines p-block elements?

  At least one p-electron in the outer shell
• What defines d-block elements?

  At least one d-electron and one s-electron
• What defines f-block elements?

  At least one f-electron and one s-electron
• What is periodicity in chemistry?

  The study of trends in the periodic table
• What happens to properties as atomic number increases?

  They show trends that repeat in periods
• What are the reactions of period 3 elements with oxygen?

  • Sodium reacts vigorously with oxygen.
  • Magnesium reacts slowly with oxygen.
  • Other reactions vary based on the element.
• What are the reactions of period 3 elements with chlorine?

  • Sodium forms sodium chloride.
  • Magnesium forms magnesium chloride.
  • Other reactions vary based on the element.
• What is the reaction of sodium with cold water?

  2Na + 2H₂O → 2NaOH + H₂
• What happens to sodium when it reacts with cold water?

  It melts and moves across the water
• What is the pH of the solution formed by sodium's reaction with water?

  pH 14
• What is the reaction of magnesium with cold water?

  Mg + 2H₂O → Mg(OH)₂ + H₂
• What is the pH of the solution formed by magnesium's reaction with water?

  pH 9−10
• What happens when magnesium is heated in steam?

  Mg + H₂O(g) → MgO + H₂
• What is the trend in atomic radius across period 3 elements?

  Atomic radius decreases across the period
• How is atomic radius measured?

  By halving the distance between nuclei
• What is the atomic radius in metals called?

  Metallic radius
• What is the atomic radius in non-metals called?

  Covalent radius
• Why does atomic radius decrease across a period?

  Nuclear charge increases, attracting electrons closer
• What is the ionic radius?

  Distance from nucleus to outermost electron of an ion
• How do cations compare to their parent atoms?

  Cations are smaller than their parent atoms
• How do anions compare to their parent atoms?

  Anions are larger than their parent atoms
• What happens to ionic radii across period 3 from Na to Cl?

  Ionic radii decrease due to increasing nuclear charge
• What is the first ionisation energy (IE)?

  Energy to remove one mole of electrons
• What is the trend in first ionisation energy across a period?

  First ionisation energy generally increases
• Why does first ionisation energy increase across a period?

  Nuclear charge increases and atomic radius decreases
• What small dips are observed in first ionisation energy?

  Between Mg-Al and P-S
• What is the trend in melting points across period 3 elements?

  Melting points rise and fall
• How do bonding and structure affect melting points in period 3 elements?

  • Na, Mg, Al: metallic bonding, higher melting points.
  • Si: giant molecular structure, highest melting point.
  • P, S, Cl, Ar: weak intermolecular forces, lower melting points.
• What type of structure do Na, Mg, and Al form?

  Giant lattice structure with delocalised electrons
• Why is the melting point of Al higher than Na?

  Stronger metallic bonding due to more electrons
• What is the highest melting point element in period 3?

  Silicon (Si)