Group 1 Elements and Alkali Metals

Characteristics of Group 1 Elements

• General Context: Group 1 elements illustrate the effect of increasing atomic size on physical and chemical properties. Their chemistry is often considered easy compared to other groups in the periodic table.
• Metallic Nature: All Group 1 elements are metals.
• Reactivity: They possess one loosely bound valence electron in their outermost shell, making them highly reactive.
• Compounds: They form univalent and colorless compounds.
• Electronegativity: These elements exhibit very low electronegativity.
• Physical Texture: The metals are soft.
• Acidity/Basicity: Their oxides and hydroxides are very strong bases.
• Bonding: They form ionic bonds with fixed oxidation states.
• Flame Colors: They exhibit characteristic colors when introduced to a flame.
• Complex Formation: They show a weak tendency to form metal complexes.

Occurrences and Sources of Alkali Metals

• Lithium ($Li$):     * It is the first element in the group and shows considerable differences from the rest of the group, a trait shared by the first elements of other groups like $Be$, $B$, and $C$.     * It is obtained as silicate minerals: Spodumene ($LiAl(SiO_3)_2$) and Lepidolite ($KLi_2Al_2(SiO_3)_3(FOH)_2$).     * Major deposits are found in the Soviet Union, Australia, China, Zimbabwe, Chile, and Canada.
• Sodium ($Na$):     * This is the most abundant metal among the Group 1 elements.     * It is found in sea water, with the largest source being rock salt ($NaCl$).     * Other sources include Borax ($Na_2B_4O_7 \cdot 10H_2O$), Sodium Carbonate ($Na_2CO_3$), Sodium Nitrate ($NaNO_3$), and Sodium Sulphate ($Na_2SO_4$).     * Deposits are obtained from the evaporation of ancient seas in the USA, China, India, and Germany.
• Potassium ($K$):     * Occurs as deposits of Sylvite ($KCl$), Sylvinite (a mixture of $KCl$ and $NaCl$), and the double salt Carnallite ($KCl \cdot MgCl_2 \cdot 6H_2O$).     * Mined deposits are typically found in Canada, Germany, France, and the USA.     * It is recovered from brines, though recovery from "normal" sea water is not considered economical.
• Rubidium ($Rb$) and Cesium ($Cs$):     * These are obtained as by-products from lithium processing and the extraction of lithium from lepidolite.
• Francium ($Fr$):     * It is a radioactive element with a short half-life of $21$ minutes.     * It does not occur appreciably in nature and is formed from the alpha decay of Actinium.

Extraction of Group 1 Metals

• General Principles: Because these metals are not found in a free state due to high reactivity and their compounds are stable to heat (making thermal decomposition difficult), they must be isolated by electrolysis of fused salts. Impurities are added specifically to lower the melting point and reduce fuel costs.
• Extraction of Sodium (Downs Cell):     * Sodium is produced via the electrolysis of molten $NaCl$ and $CaCl_2$.     * The addition of $CaCl_2$ allows the mixture to melt at $600\,^\circ C$ compared to $800\,^\circ C$ for pure $NaCl$.     * Components of the cell include a Carbon anode and an Iron cathode separated by an iron mesh. The sodium is collected in an inverted trough.     * Advantages include lowering the melting point/fuel bill and ensuring liberated sodium does not dissolve back into the melt.
• Extraction of Potassium:     * Direct electrolysis of fused $KCl$ requires high temperatures due to its high melting point, leading to the vaporization of liberated potassium.     * Modern methods use sodium vapor as a powerful reducing agent to reduce molten $KCl$.     * The reaction is carried out at $850\,^\circ C$ in a fractionating tower.
• Extraction of Rubidium and Cesium:     * These are extracted by reducing their chlorides with Calcium at $750\,^\circ C$ under reduced pressure in a fractionating tower.

Electronic Configuration

• Lithium ($Li$): Atomic Number $3$; Configuration $[He]2s^1$
• Sodium ($Na$): Atomic Number $11$; Configuration $[Ne]3s^1$
• Potassium ($K$): Atomic Number $19$; Configuration $[Ar]4s^1$
• Rubidium ($Rb$): Atomic Number $37$; Configuration $[Kr]5s^1$
• Cesium ($Cs$): Atomic Number $55$; Configuration $[Xe]6s^1$
• Francium ($Fr$): Atomic Number $87$; Configuration $[Rn]7s^1$

Trends in Physical Properties

• Atomic Radius: Increases down the group from $Li$ to $Cs$.
• Ionization Energy ($I.E.$, in unspecified units):     * $Li$: 1st $I.E. = 520$, 2nd $I.E. = 7296$     * $Na$: 1st $I.E. = 495$, 2nd $I.E. = 4563$     * $K$: 1st $I.E. = 418$, 2nd $I.E. = 3069$     * $Rb$: 1st $I.E. = 402$, 2nd $I.E. = 2650$     * $Cs$: 1st $I.E. = 375$, 2nd $I.E. = 2420$
• Electronegativity ($EN$):     * $Li$: $1.0$     * $Na$: $0.9$     * $K$: $0.8$     * $Rb$: $0.8$     * $Cs$: $0.7$
• Density ($g\,cm^{-3}$):     * The atoms are large with low densities. $Li$, $Na$, and $K$ are less dense than water ($Li$ is about half as dense).     * $Li$: $0.54$     * $Na$: $0.97$     * $K$: $0.86$     * $Rb$: $1.53$     * $Cs$: $1.90$
• Hardness, Structure, and Cohesive Energy:     * Cohesive energy is the force holding atoms together; its magnitude determines hardness. Hardness depends on the number of electrons participating in bonding.     * Metals are soft enough to be cut with a knife.     * Elements become softer down the group as atoms grow larger and bonds become weaker, causing cohesive energy to decrease.
• Melting and Boiling Points:     * Low values due to low cohesive energy, which decreases down the group.     * $Li$: MP $181\,^\circ C$, BP $1347\,^\circ C$     * $Na$: MP $98\,^\circ C$, BP $881\,^\circ C$     * $K$: MP $63\,^\circ C$, BP $766\,^\circ C$     * $Rb$: MP $39\,^\circ C$, BP $688\,^\circ C$     * $Cs$: MP $28.5\,^\circ C$, BP $705\,^\circ C$
• Flame Colors and Photovoltaic Property:     * When irradiated with light, low ionization energy allows for the emission of photoelectrons. This makes $Cs$ and $K$ useful as cathodes in photoelectric cells.     * $Li$: Crimson     * $Na$: Yellow     * $K$: Lilac     * $Rb$: Red     * $Cs$: Blue

Chemical Properties and Reactions

• Reaction with Water: React vigorously forming hydroxides and hydrogen gas. The reaction becomes more vigorous down the group.     * $2E(s) + 2H_2O(l) \rightarrow 2EOH(aq) + H_2(g)$
• Reaction with Halogens: Act as powerful reducing agents to form ionic solid halides.     * $2E(s) + X_2 \rightarrow 2EX(s)$ ($X = F, Cl, Br, I$)     * All halides form anhydrous crystals except Lithium, which forms hydrated salts ($LiX \cdot 3H_2O$) due to small size.
• Polyhalide Compounds: Alkali halides can react with halogens and interhalogen compounds.     * $KI + I_2 \rightarrow K[I_3]$     * $KBr + ICl \rightarrow K[BrICl]$
• Reaction with Hydrogen: Form ionic or salt-like hydrides ($M^+H^-$). Ease of formation decreases from $Li$ to $Cs$.     * $2M(s) + H_2(g) \rightarrow 2MH(s)$     * Hydrides are white crystalline solids with $NaCl$ structures (saline hydrides).     * $LiH + H_2O \rightarrow LiOH + H_2$ ($LiH$ is used for military purposes and meteorological balloons).     * Complex hydrides include $LiAlH_4$, $NaBH_4$, and $KBH_4$.
• Reaction with Oxygen: Form normal oxides, peroxides, or superoxides.     * Normal Oxides (Monoxides): Contain $O^{2-}$ (oxidation state -2). Soluble in water creating strong bases.         * $4Li(s) + O_2(g) \rightarrow 2Li_2O(s)$         * $Li_2O + H_2O \rightarrow 2LiOH$     * Peroxides: Contain $O_2^{2-}$ (oxidation state -1). Good oxidizing agents. $Na_2O_2$ is pale yellow and used for bleaching wood pulp, paper, and fabrics (cotton/linen).         * $2Na + O_2 \rightarrow Na_2O_2$         * $Na_2O_2 + 2H_2O \rightarrow 2NaOH + H_2O_2$ (ice-cold); at higher temperatures, $H_2O_2$ decomposes (violent reaction).         * $X_2O_2 + 2HCl \rightarrow 2XCl + H_2O_2$.     * Superoxides: Contain $O_2^-$ (oxidation state -1/2). Stronger oxidizing agents than peroxides.         * $K + O_2 \rightarrow KO_2$         * $KO_2 + 2H_2O \rightarrow KOH + H_2O_2 + \frac{1}{2}O_2$         * $KO_2$ is used in space capsules, submarines, and breathing masks to produce $O_2$ and remove $CO_2$.
• Reaction with Dinitrogen: Lithium is the only group 1 element that reacts with nitrogen.     * $6Li + N_2 \rightarrow 2Li_3N$     * $Li_3N$ decomposes into elements on heating.     * $Li_3N + 3H_2O \rightarrow 3LiOH + NH_3$
• Reaction with Sulphur: Form sulphides.     * $2Na + S \rightarrow Na_2S$     * $Na_2S + H_2O \rightarrow NaSH + NaOH$     * $Na_2S$ is used in organic sulfur dyes and the leather industry to remove hair from hides.     * $Na_2SO_4 + 4C \rightarrow Na_2S + 4CO$

Oxosalts (Carbonates, Bicarbonates, Nitrates)

• Carbonates ($M_2CO_3$): White solids; stable up to $1000\,^\circ C$ except $Li_2CO_3$.     * Ionic nature increases down the group as polarizing power decreases.     * Stability increases down the group; $K$, $Rb$, and $Cs$ carbonates are deliquescent.     * $Li_2CO_3$ decomposes on heating to $Li_2O$ and $CO_2$ because of the stable lattice of the oxide and high polarizing power of $Li$ ions.     * Solubility in water increases from $Li$ to $Cs$; $Li_2CO_3$ is the least soluble.
• Bicarbonates ($MHCO_3$): Group 1 are the only metals forming solid bicarbonates, except $LiHCO_3$ (solution only).     * Decompose to carbonates, water, and $CO_2$ on heating.     * $NaHCO_3$ is used in baking powder due to high lattice energy of $Na_2CO_3$.
• Nitrates and Nitrites: $NaNO_3$ and $NaNO_2$ are most common. $NaNO_3$ is used as fertilizer.     * Thermal stability of nitrates increases down the group.     * Nitrates (except $Li$) decompose to nitrites and oxygen: $2KNO_3(s) \rightarrow 2KNO_2(s) + O_2(g)$.     * $LiNO_3$ decomposes to oxide: $4LiNO_3(s) \rightarrow 2Li_2O(s) + 4NO_2(g) + O_2(g)$.     * $LiNO_3$ and $NaNO_3$ are deliquescent; $KNO_3$ is used in gunpowder.     * Nitrites are colorless crystalline hygroscopic solids; disproportionate on heating; produce brown $NO_2$ fumes with dilute acids.

Other Salts

• Sulphates, Hydrogen Sulphates, and Sulphites:     * All these are soluble in water.     * Sulphites react with acids to liberate $SO_2$: $Na_2SO_3(aq) + 2HCl(aq) \rightarrow 2NaCl(aq) + SO_2(g) + H_2O(l)$.     * $Na_2SO_3 + S(s) \rightarrow Na_2S_2O_3(aq)$ (Sodium thiosulphate), used in photography and iodine titrations.

Diagonal Relationship

• Certain second-period elements show chemical similarities to their diagonal neighbors in the third period (e.g., $Li$ and $Mg$).
• Causes: Arises due to effects of size and charge. Down a group, size increases; across a period, size decreases. Moving diagonally, size remains similar.
• Related to similarities in ionic size, electronegativity, and charge per unit area.

Specific Uses of Group 1 Elements

• Lithium ($Li$):     * Manufacturing alloys to improve tensile strength and corrosion resistance.     * Increases fluidity and strength/resistance of glass.     * Oxidizer in the purification of nickel and copper.     * Medicine: Citrate and salicylate forms for gout (lithium urate is soluble); mood stabilizers for bipolar disorder and schizophrenia.     * Electrochemical cells.
• Sodium ($Na$):     * Extraction of $C$, $Si$, and $Mg$.     * Reducing agent as sodium amalgam.     * Sodium vapor lamps.     * Caustic soda ($NaOH$) for soaps, paper, and inorganic/organic compounds.     * Baking powder ($NaHCO_3$).     * Liquid sodium as a coolant in nuclear reactors.     * Organic synthesis and drying organic solvents.
• Potassium ($K$):     * Electroplating.     * Extraction of gold and silver.     * Plant fertilizers and soft soap ($KOH$).     * Explosives ($KNO_3$).     * Ceramics, color TV tubes, and fluorescent tubes ($K_2CO_3$).     * Breathing apparatus and submarines ($KO_2$).