Periodicity

• What is the trend in atomic radii across period 3?

  Decreases
• Why does atomic radii decrease across period 3?

  1.) Increased nuclear charge as an increased number of protons; hence increasing the electrostatic attraction between electrons and nucleus.

  2.) shielding remains similar across the period as all electrons occupy the same shell
• Order the melting point of period 3 elements.

  (Na, Mg, Al, Si, P, S, Cl, Ar)

  1.) Si

  2.) Al

  3.) Mg

  4.) Na

  5.) S

  6.) P

  7.) Cl

  8.) Ar
• Why do the first 3 elements in period 3 increase in melting point.

  Stronger metallic bonding due to higher charged ions having a greater electrostatic attraction between delocalised electrons. Meaning a larger amount of energy is needed to overcome this attraction.
• Why does silicon have the highest melting point in period 3?

  Giant covalent (macromolecular) structure. Therefore, many strong covalent bonds meaning a large amount of energy is needed to overcome these strong covalent bonds.
• Why does phosphorous have a lower mpt than sulfur?

  Phosphorous onwards are all simple molecular structure with vanderwaals forces, meaning they all have low melting points. However, P has the formula P4, unlike sulfurs S8. Making it a slightly bigger molecule with stronger vanderwaals forces with a higher mpt.
• Describe the decrease for chlorine and argon.

  Chlorine is simple molecular and diatomic meaning it only has small van der walls forces. However, argon is an individual atom meaning its smaller therefore smaller van der waals forces and less energy needed to overcome.
• Ionisation defenition

  Minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state.
• First ionisation energy of sodium example.

  Na(g) -> Na+(g) + e-
• General trend for ionisation energy across period 3

  Increases
• Explain the general change in 1st ionisation energy across period 3.

  1.) Increased nuclear charge across the period increases the electrostatic attraction between negative electrons and positive nucleus.

  2.) Shielding going across is similar

  3.) Nuclear radius decreases

  4.) Therefore, more energy required to remove an outer electron.
• Explain the decrease in ionisation energy between magnesium and aluminum.

  Outermost electron in aluminum sits in a higher energy subshell; aluminum has a proton number of 13 therefore its outermost electron is in the 3P subshell whilst Mg is in the 3S subshell which has less shielding, therefore more electrostatic attraction between nucleus and electrons. Meaning more energy is needed to remove 1 mole of electrons.
• Explain the decrease in ionisation energy between P and S

  Sulphur has electron repulsion in its 3P subshell as it is 3P4 opposed to Phosphorous' 3P3 which is more stable. Meaning less energy is needed to remove an electron from Sulphur.
• Identify the element in period 3, from sodium to chlorine, that has the highest electronegativity


  Cl
• Is sodium or magnesium more reactive

  Sodium as the amount of energy required to remove an electron from sodium is lower than it is to remove two from magnesium,
• Sodium reaction with water

  Water: Vigorous reaction with cold water, forming a ball and fizzing. Produces hydrogen and NaOH

  2Na + 2H2O -> 2NaOH + H2
• Magnesium reaction with water

  Water: Reacts slowly forming a weak alkaline Mg(OH)2 solution as magnesium hydroxide is sparingly soluble

  Mg + 2H2O -> Mg(OH)2 + H2

  Steam: Much faster to produce MgO, a white solid and bright white light

  Mg + H2O -> MgO + H2
• Which period 3 element does not form an oxide

  Sulfur: Forms SO2 or SO3 when using high temperature and a catalyst
• Period 3 with oxygen

  • 2Na + 0.5O2 -> 2Na2O (Very fast)
  • Mg + 0.5O2 -> MgO (Very fast)
  • 2Al + 1.5O2 -> Al2O3 (Slow, fast if powdered)
  • Si + O2 -> SiO2 (Slow)
  • P4 + 5O2 -> P4O10 (Spontaneously combusts)
• Na2O, MgO and Al2O3 Melting point

  High melting points due to giant ionic lattice formation with electrostatic attraction between the cation and anion which takes lots of energy to overcome

  MgO > Al2O3 > Na2O

  (Mg forms +2 increasing the charge density, Al2O3 lower as Al+3 disorts the electron cloud of oxygen, forming covalent character)
• SiO2 melting point

  Higher melting point than the rest of the non metal oxides due do its macromolecular structure and many strong covalent bonds which require lots of energy to break
• P4O10 and SO2 mpt

  Low melting points due to the simple molecular structure with weak Van der waals forces holding them together which require less energy to break
• Oxides with water

  Na2O + H2O -> 2NaOH (Strong base as it dissolves readily)

  MgO + H2O -> Mg(OH)2 (Weak base as it dissolves sparingly in water)

  P4O10 + 6H2O -> 4H3PO4 (Triprotic acid meaning it is a strong acid)

  SO2 + H2O -> H2SO3 (Less acidic than SO3)

  SO3 + H2O -> H2SO4 (More acidic than SO2)

  SiO2 (Strong covalent structures so are insoluble in water, however they react with a base to form a salt, meaning they are classed as an acid)

  Al2O3 (Amphoteric and insoluble due to the covalent and ionic character)
• Acid-base reactions

  • MgO + 2HCl -> MgCl2 + H2O
  • Na2O + H2SO4 -> Na2SO4 + H2O
  • SiO2 + 2NaOH -> Na2SiO3 + H2O
  • P4O10 + 12NaOH -> 4Na3PO4 + 6H2O
  • SO2 + 2NaOH -> Na2SO3 + H2O
  • SO3 + 2NaOH -> Na2SO4 + H2O
  • Al2O3 + 2NaOH + 3H2O -> 2NaAl(OH)4
  • Al2O3 + 3H2SO4 -> Al2(SO4)3 + 3H2O