CHEM C9: Period 3 Physical Properties

Today we’ll be covering:

  • Periodicity of physical properties of elements in Period 3
    • Atomic radius
    • Ionic radius
    • Melting point
    • Electrical conductivity
    • 1st ionisation energy

Let’s go!


What changes as you go across Period 3?

  • the atomic number
  • the number of electrons (& thus, valence electrons)

Trends in Physical Properties:

Property

Going across Period:

Why?

Atomic Radius

Chem/Periodicity - Chubby Revision AS LevelDecreases

  • Atomic charge increases
  • Number of electrons in same principal quantum shell increases
  • Shielding effect remains constant
  • Greater attractive force
  • Valence electrons are pulled closer to nucleus

Ionic Radius

Ionic radius of Period 3 Elements | scatter chart made by ...

  • Decreases between Na+ & Si4+
  • Increases between Si4+ & P3-
  • Decreases between P3- & Cl
  • Ar does not form ion

Between Na+ & Si4+:

  • Metals lose electrons to form cations
  • They lose valence shell
  • Ionic radius is much smaller than atomic radius
  • Going across: higher nuclear charge pulls outer electrons closer

Between P3- & Cl:

  • Non-metals gain electrons to form anions
  • Valence shell contains more electrons than their atoms
  • Larger repulsion between each valence electron
  • Ionic radius is larger than atomic radius
  • Going across: higher nuclear charge pulls outer electrons closer

Melting Point

Period 3: Sodium to Argon | CapeChemistry Wiki | Fandom ...

  • Increases between Na & Al
  • Increases largely between Al & Si
  • Decreases largely between Si & P
  • Decreases between P & Ar

Between Na & Al:

  • Bonding is metallic
  • Structure is giant metallic
  • Going across: more electrons are donated into sea of delocalized electrons
  • Stronger forces of attraction
  • More energy needed to overcome

Si:

  • Bonding is covalent
  • Structure is giant covalent
  • High energy is needed to break covalent bonds

Between P & Cl:

  • Bonding is covalent
  • Structure is simple molecular
  • Weak van der Waals’ forces require less energy to break compared to metallic bonds & covalent bonds
  • Going across: structure of molecules changes
  • Smaller the size, weaker VDW forces, lower melting point
    • P: tetrahedral (large)
    • S: puckered 8-membered ring (largest)
    • Cl: diatomic (small)
    • Ar: monoatomic (smallest)

Electrical Conductivity

Period 3: Sodium to Argon | CapeChemistry Wiki | Fandom ...

  • Increases between Na & Al
    Decreases largely between Al & Si
  • Decreases between Si & S
  • Cl & Ar do not conduct

Between Na & Al:

  • Bonding is metallic
  • Structure is giant metallic
  • Going across: more electrons are donated into sea of delocalized electrons
  • Higher conductivity

Between Si & S:

  • Bonding is covalent
  • No delocalised free electrons

1st Ionisation Energy

Picture4.png

Increases, with small ‘dips’

(See here for more in-depth explanations)

  • Positive nuclear charge increases
  • Shielding effect is similar
  • Effective nuclear charge increases

Dips are due to:

  • Electronic configuration (p-orbitals vs s-orbitals)
  • Spin-pair repulsion (p1 vs p2)

 

One thought on “CHEM C9: Period 3 Physical Properties

  1. Irfan

    The radius of Ar is actually higher: this is because Ar has VDW forces, so the distance between atoms is larger (because of electron repulsion)

    Like

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