Scandium (Sc) - Atomic Structure and Properties

Atomic Model Details

Scandium (Sc) is the first element of the d-block in the periodic table, belonging to Group 3 and Period 4.

• Atomic Number (Z): 21
  • Indicates 21 protons in the nucleus.
  • In a neutral Scandium atom, there are 21 electrons.
• Mass Number (A): The most stable and common isotope, Scandium-45 ($^{45}\text{Sc}$), has a mass number of 45.
• Neutrons: For $^{45}\text{Sc}$, the number of neutrons is A - Z = 45 - 21 = 24.
• Atomic Size:
  • Metallic Radius: Approximately 162 pm (picometers). This value reflects the size of the atom in a metallic crystal lattice.

Electronic Configuration & Shell Diagram Representation

• Ground State Electronic Configuration (Full): $1s^2 2s^2 2p^6 3s^2 3p^6 3d^1 4s^2$

• Ground State Electronic Configuration (Condensed): $[\text{Ar}] 3d^1 4s^2$

  • The $[\text{Ar}]$ represents the electronic configuration of Argon ($1s^2 2s^2 2p^6 3s^2 3p^6$).

• Shell Diagram Representation (in text):

  • K-shell (n=1): 2 electrons ($1s^2$)
  • L-shell (n=2): 8 electrons ($2s^2 2p^6$)
  • M-shell (n=3): 9 electrons ($3s^2 3p^6 3d^1$)
  • N-shell (n=4): 2 electrons ($4s^2$)

  This distribution indicates that Scandium has two valence electrons in its outermost (N) shell, and one electron in the penultimate (M) 3d subshell.

Periodic Trends

Ionization Enthalpy (Energy required to remove an electron)

• First Ionization Enthalpy ($\Delta H_{i1}$): 633.1 kJ/mol
  • Corresponds to the removal of an electron from the $4s$ subshell.
• Second Ionization Enthalpy ($\Delta H_{i2}$): 1235 kJ/mol
  • Corresponds to the removal of the second electron from the $4s$ subshell.
• Third Ionization Enthalpy ($\Delta H_{i3}$): 2389 kJ/mol
  • Corresponds to the removal of the electron from the $3d$ subshell.
  • The relatively large jump from $\Delta H_{i3}$ to $\Delta H_{i4}$ (approximately 7091 kJ/mol, not typically required for high school but for context) signifies the stability of the noble gas core after losing the three valence electrons ($4s^2 3d^1$).

Electronegativity (Pauling Scale)

• Electronegativity: 1.36
  • Scandium is an electropositive element, characteristic of metals, and readily forms positive ions.

Electron Gain Enthalpy (Energy change when an electron is added)

• Electron Gain Enthalpy ($\Delta H_{eg}$): -18 kJ/mol (exothermic)
  • Indicates a slight tendency to accept an additional electron, though it is not a prominent characteristic for metals.

Atomic Radius

• Metallic Radius: 162 pm
• Ionic Radius (for Sc$^{3+}$ ion): Approximately 74.5 pm
  • The significant reduction in size upon forming a Sc$^{3+}$ ion is due to the loss of all three valence electrons and the exposure of the smaller noble gas core.

Key Physical Properties

• Density: 2.99 g/cm$^3$ at 25 °C
  • Relatively low density for a transition metal.
• State at Room Temperature (25 °C): Solid
• Color: Silvery-white metal (tarnishes to a yellowish or pinkish hue when exposed to air).
• Melting Point (MP): 1541 °C (1814 K)
• Boiling Point (BP): 2836 °C (3109 K)