Inorganic Chemistry: Noble Gases, Halogens, Transition Metals, and Alloys Study Guide

Group VIII (Group 18) Noble Gases

• Identification of Group VIII Elements: The noble gases include Helium ($He$), Neon ($Ne$), Argon ($Ar$), Krypton ($Kr$), Xenon ($Xe$), and Radon ($Rn$).
• General Physical Properties:     * They are unreactive, monatomic (exist as single atoms) gases at room temperature and pressure (r.t.p.).     * They are categorized by having all occupied electron shells completely filled.
• Electronic Configuration and High Stability:     * Helium has a full first shell with the configuration $1s^2$.     * Other noble gases (Neon to Radon) have a general outer-shell configuration of $ns^2 np^6$.     * A full outer shell is energetically very stable. Because of this, atoms do not need to gain, lose, or share electrons, making them chemically inert (they do not readily form chemical bonds).
• Ionisation Energies and Electronegativity:     * Ionisation Energies: These are very high because electrons are tightly held by the nucleus, requiring a massive amount of energy to remove one. This makes ion formation extremely difficult.     * Electronegativity: They possess zero or near-zero electronegativity, meaning they have no tendency to attract electrons.
• Behavior in Mixtures: When noble gases of different masses (e.g., Helium and Argon) are mixed in a closed container at r.t.p., they become evenly mixed throughout the container despite their difference in mass.

Group VII Halogens

• Characteristics and Member Elements: Group VII includes Fluorine ($F$), Chlorine ($Cl$), Bromine ($Br$), Iodine ($I$), and Astatine ($At$).
• Appearance at Room Temperature and Pressure:     * Chlorine: A green gas.     * Bromine: A reddish-brown liquid consisting of $Br_2$ molecules.     * Iodine: A grey-black solid. When heated, it produces a purple vapor. In solid form, its particles (molecules) vibrate about fixed points in a molecular lattice.
• Trends in Physical Properties:     * Boiling Point: Increases as the group is descended because the intermolecular forces become stronger and harder to break.     * Color: The elements become darker in colour as the relative molecular mass increases.     * Volatility: Decreases as the relative molecular mass increases.
• Reactivity Trends and Explanations:     * Reactivity decreases down the group (F > Cl > Br > I > At).     * Nuclear Attraction: When halogens react, they form $1-$ ions by attracting an electron. A smaller atom (like Chlorine) has its outer shell closer to the nucleus compared to a larger atom (like Bromine). Therefore, the incoming electron is more strongly attracted to the nucleus in smaller atoms.     * Oxidising Ability: The ability to act as an oxidising agent (removing electrons from other species) falls down the group. Chlorine is a stronger oxidising agent than Bromine, and Bromine is stronger than Iodine.
• Displacement Reactions:     * A more reactive halogen will displace a less reactive halogen from its aqueous halide solution.     * Reaction with Chlorine: Chlorine can displace both Bromine and Iodine.         * Cl_2(aq) + 2KBr(aq) ightarrow 2KCl(aq) + Br_2(aq) (The colorless solution turns orange/reddish-brown due to Bromine formation).         * Cl_2(aq) + 2KI(aq) ightarrow 2KCl(aq) + I_2(aq) (The colorless solution turns dark reddish-brown or forms a grey precipitate of Iodine).     * Reaction with Bromine: Bromine can displace Iodine but not Chlorine.         * Br_2(aq) + 2KI(aq) ightarrow 2KBr(aq) + I_2(aq).
• Reactions with Metals and Hydrogen:     * Group 1 and 2 Metals: Halogens react with metals to form ionic compounds. For example, Sodium burns in Chlorine with an orange flame to produce white solid Sodium Chloride (2Na(s) + Cl_2(g) ightarrow 2NaCl(s)).     * Reaction with Hydrogen: Forms hydrogen halides (H_2(g) + X_2(g) ightarrow 2HX(g)).         * Fluorine: Violent explosion even in the cold and dark.         * Chlorine: Violent explosion in sunlight or flame.         * Bromine: Mild explosion with a flame.         * Iodine: Partial reaction requiring continuous heating.
• Hydrogen Chloride ($HCl$) and Hydrochloric Acid:     * $HCl$ gas is a colorless, poisonous, acidic gas that is very soluble in water.     * In water, $HCl$ dissociates into $H^+(aq)$ (hydroxonium ions) and $Cl^-(aq)$, showing acidic properties (turns damp blue litmus red, reacts with metals and carbonates).     * In organic solvents (like methyl benzene/toluene), $HCl$ does not dissociate and does not show acidic properties (will not turn dry litmus red or react with Magnesium).
• Isotopes of Bromine: Naturally occurring Bromine has a relative atomic mass of $80$, consisting of two isotopes ($^{79}Br$ and $^{81}Br$) in roughly equal proportions ($50:50$). These isotopes have the same number of protons and electrons and identical chemical properties, but different numbers of neutrons and different physical properties.

Transition Elements

• Location: Found in the block between Group 2 and Group 3 of the periodic table.
• General Physical Properties:     * They are typical metals: strong, hard, and dense.     * They have high melting points (e.g., Copper melts at $1083\,^\circ\text{C}$, while Sodium has a much lower melting point and density).     * They are excellent conductors of heat and electricity.
• Chemical Characteristics:     * Variable Oxidation States: They can form ions with different charges. For example, Iron forms $Fe^{2+}$ and $Fe^{3+}$; Copper forms $Cu^+$ and $Cu^{2+}$.     * Coloured Compounds: Their ions often have characteristic colours in solution:         * Copper(II) ($Cu^{2+}$): Blue.         * Iron(II) ($Fe^{2+}$): Pale green.         * Iron(III) ($Fe^{3+}$): Yellow or green (e.g., $FeCl_3$ is yellow).         * Manganate(VII) ($MnO_4^-$): Purple.         * Dichromate(VI) ($Cr_2O_7^{2-}$): Orange.         * Nickel(II) ($Ni^{2+}$): Green.
• Catalytic Uses: Transition metals and their compounds are frequently used as industrial catalysts:     * Iron: Used in the Haber Process for the manufacture of Ammonia ($NH_3$).     * Vanadium(V) Oxide ($V_2O_5$): Used in the Contact Process for the manufacture of Sulfuric Acid ($H_2SO_4$).     * Nickel: Used in the manufacture of margarine (hydrogenation of unsaturated vegetable oils).     * Platinum: Used in the manufacture of Nitric Acid.     * Copper(II) Sulfate: Can also act as a catalyst in various reactions.

Alloys

• Definition: An alloy is a mixture of a metal with other elements (which can be other metals or non-metals like Carbon).
• Structure and Strength:     * In a pure metal, atoms are the same size and arranged in regular layers that can easily slide over each other when a force is applied.     * In an alloy, different-sized atoms disrupt the regular lattice. This prevents the layers from sliding easily, making alloys harder and stronger than pure metals.
• Common Alloys and Compositions:     * Brass: $70\%$ Copper ($Cu$) and $30\%$ Zinc ($Zn$). Properties: Harder than pure copper, 'gold' coloured. Uses: Musical instruments, ornaments, electrical connections.     * Bronze: $90\%$ Copper ($Cu$) and $10\%$ Tin ($Sn$). Properties: Harder than pure copper. Uses: Statues, bells, machine parts.     * Mild Steel: $99.7\%$ Iron ($Fe$) and $0.3\%$ Carbon ($C$). Properties: Stronger and harder than pure iron. Uses: Car bodies.     * Stainless Steel: Iron ($74\%$), Chromium ($18\%$), Nickel ($8\%$), and Carbon. Properties: Harder than pure iron, resistant to rusting/corrosion. Uses: Cutlery, surgical instruments, chemical reaction vessels.     * Solder: $50\%$ Tin ($Sn$) and $50\%$ Lead ($Pb$). Properties: Lower melting point than either constituent metal. Use: Making electrical connections.     * Aluminium Alloys: Mixed with Copper, Manganese, and Silicon. Properties: Stronger than pure aluminium but retains low density. Use: Aircraft bodies.

Reactivity Series and General Metal Properties

• The Reactivity Series: Decreasing order of reactivity: K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag.
• Displacement Reactions in Metals: A metal higher in the reactivity series can displace a metal lower in the series from its aqueous solution (e.g., Zinc will displace Copper from Copper Sulfate solution).
• Stability of Metal Compounds:     * Compounds of highly reactive metals (top of the series) are stable and do not decompose easily on heating.     * Compounds of less reactive metals (bottom of the series) decompose more readily. For example, Carbonates decompose to oxides and $CO_2$ (e.g., $ZnCO_3(s) \rightarrow ZnO(s) + CO_2(g)$).
• Aluminium and Corrosion: Aluminium is naturally reactive but resistant to corrosion because it forms a tough, unreactive layer of Oxide ($Al_2O_3$) on its surface. It is used in overhead electrical cables because it is a good conductor, has low density, and is ductile.
• Extraction: Oxides of metals low in the series can be reduced by Carbon or Hydrogen ($reduction$).

Questions & Discussion

• Q: Why are Helium and Neon unreactive?     * A: Because they both have all their occupied electron shells completely filled.
• Q: Why does Chromium have different physical properties than Sodium?     * A: Chromium is a transition metal, meaning it is denser, harder, and has a higher melting point than Group 1 Sodium.
• Q: What is the effect of temperature on diffusion?     * A: Diffusion rates increase with temperature because particles gain more kinetic energy and move faster.
• Q: Explain the redox nature of the reaction $2Br^-(aq) + Cl_2(aq) \rightarrow Br_2(aq) + 2Cl^-(aq)$.     * A: Bromide ions ($Br^-$) are oxidized because they lose electrons. Chlorine ($Cl_2$) is reduced because it gains electrons.