Study Notes on Metallic Bonds and Alloys

Discussions of bonding types common in questions:
- Covalent Network Bonds
- Ionic Bonds
- Metallic Bonds

Definition of Metallic Bonds:
- Electron sharing among atoms, specifically delocalized electrons which contribute to bonding characteristics.
Structure of Metallic Bonds:
- Atoms are closely packed together and the electrons are not localized but rather shared across all atoms, leading to a structure often represented with a positive charge symbolizing the atomic nuclei.
Key Properties of Metallic Bonds:
- Good conductors of heat and electricity: Due to the movement of delocalized electrons.
- High melting points: Characteristic of strong metallic bonds.
- Malleability: Metals can be shaped and bent due to their layered structure.
- Ductility: Metals can be drawn into wires without breaking.

The layers of atoms in a metallic bond allow them to shift when pressure is applied without breaking the bond, hence the ability to bend or pull into wires.

Analysis of Group 1 Metals (Alkali Metals):
- Example: Lithium (Li), Sodium (Na), Potassium (K).
- Trend: As the atomic size increases, the melting point decreases.
- Explanation: As atoms get larger, the attractive force among them decreases due to the increased distance between electrons and nuclei, thus reducing the melting temperature.
Comparison with Group 17 (Halogens):
- Example: Diatomic elements like F₂, Cl₂, Br₂.
- These molecules are nonpolar and held together by Intermolecular Forces (IMFs).
- Trend: As atomic size increases (or molecular size), the melting temperature increases due to the polarizability of electrons. More electrons make it easier to form temporary dipoles, leading to stronger IMFs in larger molecules.

Chemical Change Explanation:
- Splitting diatomic molecules involves breaking covalent bonds, which constitutes a chemical reaction.
- Intra-molecular forces require significant energy to break, emphasizing the chemical change involved when bonds are split.

Definition of Alloys:
- Mixtures of different elements, typically two metals.
Types of Alloys:
- Substitutional Alloys:
- Made from metals that have similar atomic sizes.
- Example: Zinc and Copper are close in size, where Copper is slightly larger.
- Key characteristic: Atoms in substitutional alloys can replace each other in the crystal lattice without significant difference in size.
- Interstitial Alloys:
- Formed when one metal is much smaller than the other, allowing smaller atoms to fit in the spaces (interstices) between the larger atoms.
- Example: Mixing Carbon with Iron creates an interstitial alloy because Carbon is significantly smaller than Iron.
Important Note About Sizes in Alloys:
- While substitutional alloy components will have closely related atomic radii, interstitial alloys require a significant size disparity.