krit.club logo

Chemical Bonding - Electron Sea Model-advanced

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

The Electron Sea Model (or Drude-Lorentz Model) describes metallic bonding as an array of positive metal ions (called Kernels) held together by a 'sea' of mobile, delocalized valence electrons.

•

Delocalization occurs because metals have low ionization energies, allowing their valence electrons to detach easily and move freely throughout the entire crystal lattice rather than being confined to a single atom.

•

The metallic bond is the strong electrostatic force of attraction between the positively charged metal kernels and the negatively charged mobile electrons.

•

Electrical Conductivity: Metals are excellent conductors because the delocalized electrons can move freely in response to an electric field. The current is carried by the flow of these electrons.

•

Thermal Conductivity: Heat energy is transferred through metals via the increased kinetic energy and rapid movement of the delocalized electrons, as well as the vibrations of the kernels.

•

Malleability and Ductility: Metallic bonds are non-directional. When a force is applied, layers of kernels can slide over each other. The 'sea' of electrons adjusts to the new positions, preventing the crystal from fracturing.

•

Metallic Lustre: The mobile electrons on the surface of the metal can absorb and re-emit light of various frequencies, giving metals their characteristic shine.

•

The strength of the metallic bond increases with the number of valence electrons and the decrease in the size of the metal atom.

📐Formulae

Bond Strength∝Number of Valence ElectronsAtomic RadiusBond\ Strength \propto \frac{Number\ of\ Valence\ Electrons}{Atomic\ Radius}

Total Charge of Kernels+Total Charge of Delocalized Electrons=0Total\ Charge\ of\ Kernels + Total\ Charge\ of\ Delocalized\ Electrons = 0

n=N×dMn = \frac{N \times d}{M}

💡Examples

Problem 1:

Compare the metallic bond strength of Sodium (NaNa, Atomic Number 1111) and Magnesium (MgMg, Atomic Number 1212).

Solution:

  1. Electronic configuration of NaNa is 2,8,12, 8, 1. It contributes 11 electron to the sea.
  2. Electronic configuration of MgMg is 2,8,22, 8, 2. It contributes 22 electrons to the sea.
  3. Mg2+Mg^{2+} kernels have a higher positive charge than Na+Na^{+} kernels.
  4. MgMg atoms are smaller in size compared to NaNa atoms.
  5. Therefore, the electrostatic attraction in MgMg is much stronger than in NaNa.

Explanation:

According to the Electron Sea Model, bond strength is directly proportional to the number of delocalized electrons and inversely proportional to the atomic radius. Since MgMg has more valence electrons and a smaller radius, it has a higher melting point and is harder than NaNa.

Problem 2:

Why does the electrical conductivity of a metal decrease when the temperature is increased?

Solution:

  1. As temperature increases, the positive metal kernels gain kinetic energy and begin to vibrate more vigorously about their fixed positions.
  2. These vibrations create 'lattice distortions'.
  3. The path of the delocalized electrons is obstructed by these vibrating kernels, leading to more frequent collisions.
  4. This increased resistance hinders the flow of electrons, thereby decreasing conductivity.

Explanation:

In the Electron Sea Model, while the 'sea' moves to conduct electricity, the 'kernels' are fixed but vibrating. High temperature increases kernel vibration, acting as a physical barrier to the flow of the electron sea.

Problem 3:

Represent the formation of the metallic lattice for Aluminum (AlAl).

Solution:

Al→Al3++3e−Al \rightarrow Al^{3+} + 3e^{-} In the lattice: Al3+e−e−e−Al3+e−e−e−Al3+e−e−e−Al3+e−e−e−Al3+e−e−e−Al3+e−e−e−Al3+e−e−e−Al3+\begin{array}{ccccc} Al^{3+} & e^{-}e^{-}e^{-} & Al^{3+} & e^{-}e^{-}e^{-} & Al^{3+} \\ e^{-}e^{-}e^{-} & Al^{3+} & e^{-}e^{-}e^{-} & Al^{3+} & e^{-}e^{-}e^{-} \\ Al^{3+} & e^{-}e^{-}e^{-} & Al^{3+} & e^{-}e^{-}e^{-} & Al^{3+} \end{array}

Explanation:

Each Aluminum atom contributes 3 valence electrons to the delocalized sea. The resulting Al3+Al^{3+} kernels are held together by the attraction to these 3n3n electrons (where nn is the number of atoms), creating a very strong metallic bond.