Unit 9: Comprehensive Summary

Elements are broadly classified into metals, non-metals, and metalloids.

• Metals: Characterized by metallic bonding (a lattice of positive ions in a "sea" of delocalized electrons). This structure explains their key physical properties: electrical and thermal conductivity, malleability, ductility, and lustre. The strength of the metallic bond depends on cation charge, cation size, and the number of delocalized electrons.
• Non-metals: Held together by strong, directional covalent bonds. Electrons are localized, making them poor conductors.
• Metalloids: Have intermediate properties and are primarily used as semiconductors (e.g., Silicon).
• Reactivity: Metals are ranked in a reactivity series based on their tendency to be oxidized. A more reactive metal can displace a less reactive metal from its salt solution. This is quantified by standard electrode potentials ($E^\circ$), where a more negative value indicates a more reactive metal.

• s-block Metals (e.g., Na, Ca): Are highly reactive. They react vigorously with water to form a metal hydroxide and hydrogen gas, and with acids to form a salt and hydrogen gas. They tarnish quickly in air.
• p-block Metals (e.g., Al): Less reactive. Aluminum is protected by a tough, non-porous layer of aluminum oxide ($Al_2O_3$), a process called passivation. This layer makes it resistant to corrosion.
• d-block Metals (e.g., Fe, Cu): Generally unreactive. Iron rusts in the presence of both oxygen and water, forming flaky, non-protective hydrated iron(III) oxide. Copper and gold are very unreactive with air, water, and dilute acids.
• Transition Metals: A subset of d-block metals that form at least one stable ion with a partially filled d-subshell. This leads to unique properties like having variable oxidation states and acting as effective catalysts.

Metal extraction from an ore is a reduction process. The method depends on the metal's reactivity.

• Electrolysis: Used for highly reactive metals like Aluminum. In the Hall-Héroult process, aluminum oxide is dissolved in molten cryolite to lower the temperature, and electricity is used to reduce $Al^{3+}$ ions to Al metal.
• Reduction with Carbon: Used for less reactive metals like Iron. In a blast furnace, iron ore is heated with coke (carbon) and limestone. Carbon monoxide is the main reducing agent, and limestone removes silica impurities as slag.
• Uses & Alloys: A metal's use is tied to its properties (e.g., Al for aircraft due to low density; Cu for wires due to conductivity). Alloys (e.g., steel, brass, bronze) are mixtures created to improve properties like hardness and corrosion resistance.

• s-block Compounds: Typically white solids forming colorless solutions (e.g., NaCl, NaOH, CaO, CaCO₃). They have widespread uses as salts, bases, and industrial chemicals.
• d-block Compounds: Often colored due to the formation of complex ions. A complex ion has a central metal ion bonded to ligands via dative covalent bonds. The ligands split the d-orbitals, allowing for the absorption of visible light.
• Hydrated Salts: Compounds with water of crystallization in their structure. The color change between anhydrous and hydrated copper(II) sulfate ($CuSO_4$) serves as the chemical test for water (white to blue).
• Qualitative Analysis: Cations can be identified by their reactions with NaOH and NH₃. The formation of precipitates, their colors, and whether they redissolve in excess reagent (due to being amphoteric or forming a complex ion) are key observations.