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Chemistry p-Block Elements

p-Block Elements Formula Sheet

All key reactions, periodic trends, structures and oxidation-state facts for p-Block Groups 13-18 and oxoacids - JEE Main & Advanced quick revision.

13 min read Updated Jun 2026 #formula sheet#quick revision#jee-main

Last-minute revision sheet for the entire p-Block chapter (Groups 13-18 plus oxoacids). This is a descriptive chapter, so the emphasis is on key reactions, structures, periodic trends and oxidation-state facts rather than numerical formulas. Everything here is distilled from the chapter topic pages.

How to use this sheet

Scan the trend tables first, then the boxed headline reactions per group, then the structure/shape tables. The “Common Traps” callouts are the highest-yield exam savers.

Valence configuration: $ns^2 np^{1-6}$. Across and down the block, the recurring trends are:

PropertyDown a groupReason
Atomic / ionic radiusIncreasesAdditional shells added
Ionization energyDecreasesIncreased shielding (exceptions: Ga > Al)
ElectronegativityDecreasesNuclear attraction weakens
Metallic characterIncreasesNon-metal $\rightarrow$ metalloid $\rightarrow$ metal
Stability of lower oxidation stateIncreasesInert pair effect
Inert pair effect
Stability of the lower oxidation state increases down a group: Tl(+1) > Tl(+3); Pb(+2) > Pb(+4); Bi(+3) stable. The $ns^2$ pair becomes reluctant to participate in bonding.

Group 13 - Boron Family (B, Al, Ga, In, Tl)

Configuration $ns^2 np^1$; common oxidation state +3, +1 for Tl (inert pair).

TrendDirectionNote
Ionization energyDecreases down, but Ga > Ald-block contraction / poor d-shielding in Ga
Metallic characterB is non-metal; Al, Ga, In, Tl metals

Borax and Boric Acid

$$\boxed{Na_2B_4O_7 + 7H_2O \rightarrow 2NaOH + 4H_3BO_3}$$
ReactionEquation
Borax hydrolysis (alkaline)$Na_2B_4O_7 + 7H_2O \rightarrow 2NaOH + 4H_3BO_3$
Borax bead (heating)$Na_2B_4O_7 \xrightarrow{\Delta} 2NaBO_2 + B_2O_3$
Bead colour$B_2O_3 + CoO \rightarrow Co(BO_2)_2$ (blue bead)
Boric acid from borax$Na_2B_4O_7 + 2HCl + 5H_2O \rightarrow 2NaCl + 4H_3BO_3$
Boric acid as Lewis acid$B(OH)_3 + 2H_2O \rightarrow [B(OH)_4]^- + H_3O^+$
Heating boric acid$H_3BO_3 \xrightarrow{373K} HBO_2 \xrightarrow{red\ heat} B_2O_3$
Green-flame test$H_3BO_3 + 3C_2H_5OH \rightarrow B(OC_2H_5)_3 + 3H_2O$
Common trap - boric acid
$H_3BO_3$ is a monobasic Lewis acid that accepts $OH^-$, NOT a Bronsted acid donating $H^+$ from its three OH groups.

Diborane and Borazine

$$\boxed{B_2H_6 + 6H_2O \rightarrow 2B(OH)_3 + 6H_2}$$
ReactionEquation
Diborane preparation$3NaBH_4 + 4BF_3 \rightarrow 2B_2H_6 + 3NaBF_4$
Alternative prep$2BF_3 + 6LiH \xrightarrow{450K} B_2H_6 + 6LiF$
Hydrolysis$B_2H_6 + 6H_2O \rightarrow 2B(OH)_3 + 6H_2$
Combustion (rocket fuel)$B_2H_6 + 3O_2 \rightarrow B_2O_3 + 3H_2O$
Borazine (inorganic benzene)$3B_2H_6 + 6NH_3 \rightarrow 2B_3N_3H_6 + 12H_2$

Diborane structure: 2 bridging H (3-centre-2-electron “banana” bonds) + 4 terminal H (normal 2c-2e bonds).

Aluminium

ReactionEquation
Baeyer’s purification$Al_2O_3{\cdot}2H_2O + 2NaOH \rightarrow 2NaAlO_2 + 3H_2O$
With acid (amphoteric)$2Al + 6HCl \rightarrow 2AlCl_3 + 3H_2$
With base (amphoteric)$2Al + 2NaOH + 2H_2O \rightarrow 2NaAlO_2 + 3H_2$
Thermite$Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3$
  • Ores: Bauxite ($Al_2O_3{\cdot}2H_2O$), Corundum ($Al_2O_3$), Cryolite ($Na_3AlF_6$).
  • Extraction: Hall-Heroult electrolysis. Cathode: $Al^{3+} + 3e^- \rightarrow Al$.
  • Passivation: Al becomes passive in conc. $HNO_3$ (protective oxide layer).
  • AlCl₃ exists as the dimer $Al_2Cl_6$ (coordinate bonds); a Lewis acid (Friedel-Crafts catalyst).
  • Alum general formula: $M_2SO_4{\cdot}M'_2(SO_4)_3{\cdot}24H_2O$ (e.g. potash alum $K_2SO_4{\cdot}Al_2(SO_4)_3{\cdot}24H_2O$).

Diagonal relationship: B resembles Si (both metalloids; acidic oxides $B_2O_3$, $SiO_2$; chlorides hydrolyse).

Group 14 - Carbon Family (C, Si, Ge, Sn, Pb)

Configuration $ns^2 np^2$; oxidation states +4, +2 (+2 more stable down the group).

$$\boxed{\text{Catenation: } C \gg Si > Ge > Sn > Pb}$$
PropertyTrendNote
Metallic characterC, Si non-metals; Ge metalloid; Sn, Pb metals
M-M bond strengthDecreasesC-C (348) > Si-Si (226) kJ/mol
Stable oxidation state+4 for C; +2 for PbInert pair effect

Allotropes of Carbon

AllotropeHybridisationStructureConductivityC-C length
Diamond$sp^3$3D networkInsulator154 pm
Graphite$sp^2$2D layersConductor141.5 pm (in plane), 335 pm layer gap
Fullerene ($C_{60}$)$sp^2$Soccer ball (12 pentagons + 20 hexagons)Poor
Graphene$sp^2$Single graphite sheetExcellent

Oxides of Carbon

ReactionEquation
CO lab prep$HCOOH \xrightarrow{conc.\ H_2SO_4} CO + H_2O$
Metal carbonyl$Ni + 4CO \rightarrow Ni(CO)_4$
$CO_2$ lab prep$CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2$
Lime-water test$CO_2 + Ca(OH)_2 \rightarrow CaCO_3 + H_2O$
Excess $CO_2$ (clears)$CaCO_3 + H_2O + CO_2 \rightarrow Ca(HCO_3)_2$
Burns Mg$CO_2 + 2Mg \rightarrow 2MgO + C$
  • CO is neutral (toxic; binds Hb 300x stronger than $O_2$); $CO_2$ is acidic (linear, sp).

Silicon Compounds

$$\boxed{SiCl_4 + 2H_2O \rightarrow SiO_2 + 4HCl} \qquad (CCl_4 \text{ does NOT hydrolyse})$$
ReactionEquation
Ultrapure Si$SiCl_4 + 2H_2 \rightarrow Si + 4HCl$ (1000°C, then zone refining)
$SiO_2$ + base$SiO_2 + 2NaOH \rightarrow Na_2SiO_3 + H_2O$
HF attacks silica$SiO_2 + 4HF \rightarrow SiF_4 + 2H_2O$
$SiO_2$ + carbon$SiO_2 + 2C \rightarrow Si + 2CO$
Silicone monomer$2CH_3Cl + Si \xrightarrow{Cu,\ 570K} (CH_3)_2SiCl_2$
  • Silicones (polysiloxanes): Si-O backbone with R groups; water-repellent, heat-resistant; general $R_2SiO$.
  • Silicates: basic unit $SiO_4^{4-}$ tetrahedron. Sharing of 0/1/2/2/3/4 corners gives ortho / pyro / cyclic / chain / sheet / 3D-network silicates.
  • Zeolites: 3D aluminosilicates ($SiO_4$ + $AlO_4$); molecular sieves, ion-exchange water softeners.
  • Why $SiCl_4$ hydrolyses, $CCl_4$ doesn’t: Si has vacant d-orbitals (can expand octet); C has none.

Tin and Lead

ReactionEquation
$PbI_2$ yellow ppt test$Pb(NO_3)_2 + 2KI \rightarrow PbI_2 + 2KNO_3$
$PbO_2$ oxidation$PbO_2 + 4HCl \rightarrow PbCl_2 + Cl_2 + 2H_2O$
  • Tin pest: $\beta$-Sn $\rightarrow$ $\alpha$-Sn below 13.2°C.
  • Lead oxides: PbO (litharge, amphoteric), $Pb_3O_4$ (red lead), $PbO_2$ (strong oxidiser).

Group 15 - Nitrogen Family (N, P, As, Sb, Bi)

Configuration $ns^2 np^3$; oxidation states -3, +3, +5. Hydride basicity: $NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$.

Dinitrogen and Ammonia

$$\boxed{N \equiv N \text{ bond energy} = 946\ \text{kJ/mol (very unreactive)}}$$$$\boxed{N_2 + 3H_2 \underset{Fe}{\overset{450°C,\ 200\ atm}{\rightleftharpoons}} 2NH_3 \qquad \Delta H = -92\ \text{kJ/mol}}$$
ReactionEquation
$N_2$ lab prep$NH_4Cl + NaNO_2 \rightarrow N_2 + 2H_2O + NaCl$
Haber process$N_2 + 3H_2 \rightleftharpoons 2NH_3$ (Fe + $K_2O$, $Al_2O_3$ promoters)
$NH_3$ lab prep$2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2H_2O + 2NH_3$
$NH_3$ + HCl (white fumes)$NH_3 + HCl \rightarrow NH_4Cl$
Reducing$2NH_3 + 3CuO \rightarrow 3Cu + N_2 + 3H_2O$
Complex (deep blue)$CuSO_4 + 4NH_3 \rightarrow [Cu(NH_3)_4]SO_4$
  • $NH_3$ structure: pyramidal, $sp^3$, bond angle 107°, $\mu = 1.46$ D, $K_b = 1.8\times10^{-5}$.

Oxides of Nitrogen

OxideN stateColourNature
$N_2O$+1ColourlessNeutral
NO+2ColourlessNeutral (paramagnetic)
$N_2O_3$+3BlueAcidic
$NO_2$+4BrownAcidic (paramagnetic)
$N_2O_4$+4ColourlessAcidic
$N_2O_5$+5White solidAcidic
  • $2NO + O_2 \rightarrow 2NO_2$; $\;2NO_2 \rightleftharpoons N_2O_4$ (dimerisation on cooling).

Nitric Acid (Ostwald Process)

$$\boxed{4NH_3 + 5O_2 \xrightarrow{Pt-Rh,\ 800°C} 4NO + 6H_2O}$$
StepEquation
Ostwald 1$4NH_3 + 5O_2 \rightarrow 4NO + 6H_2O$
Ostwald 2$2NO + O_2 \rightarrow 2NO_2$
Ostwald 3$4NO_2 + O_2 + 2H_2O \rightarrow 4HNO_3$
Cu + dil. $HNO_3$$3Cu + 8HNO_3 \rightarrow 3Cu(NO_3)_2 + 2NO + 4H_2O$
Cu + conc. $HNO_3$$Cu + 4HNO_3 \rightarrow Cu(NO_3)_2 + 2NO_2 + 2H_2O$
Aqua regia (3:1 HCl:$HNO_3$)$Au + 4HCl + HNO_3 \rightarrow HAuCl_4 + NO + 2H_2O$
Ring test$NO + [Fe(H_2O)_6]^{2+} \rightarrow [Fe(H_2O)_5(NO)]^{2+} + H_2O$ (brown ring)
Common traps - HNO₃

Dilute $HNO_3$ $\rightarrow$ NO; concentrated $\rightarrow$ $NO_2$; very dilute with Zn $\rightarrow$ $N_2O$ / $NH_4NO_3$.

Passivation by conc. $HNO_3$: only Fe, Al, Cr (NOT Mg, Mn).

Aqua regia ratio is 3 HCl : 1 $HNO_3$.

Phosphorus

$$\boxed{2Ca_3(PO_4)_2 + 6SiO_2 + 10C \xrightarrow{1775K} P_4 + 6CaSiO_3 + 10CO}$$
PropertyWhite $P_4$Red P
StructureTetrahedral $P_4$ (angle 60°)Polymeric chain
ReactivityVery reactive, pyrophoricLess reactive
Ignition35°C260°C
ToxicityPoisonousNon-poisonous
StorageUnder waterOpen air
  • White $\rightarrow$ Red: $P_4(white) \xrightarrow{573K} P(red)$ (inert atmosphere). Black P is most stable, a conductor.

Phosphine and Phosphorus Oxides

ReactionEquation
$PH_3$ lab prep$P_4 + 3NaOH + 3H_2O \rightarrow PH_3 + 3NaH_2PO_2$
Pure $PH_3$$Ca_3P_2 + 6H_2O \rightarrow 3Ca(OH)_2 + 2PH_3$
$P_4O_6$$P_4 + 3O_2 \rightarrow P_4O_6$
$P_4O_{10}$$P_4 + 5O_2 \rightarrow P_4O_{10}$
$P_4O_{10}$ dehydration$4HNO_3 + P_4O_{10} \rightarrow 2N_2O_5 + 4HPO_3$
  • $PH_3$ structure: pyramidal, bond angle 93.5° (less than $NH_3$); less basic than $NH_3$. $P_4O_{10}$ is an excellent dehydrating agent.

Group 16 - Oxygen Family / Chalcogens (O, S, Se, Te, Po)

Configuration $ns^2 np^4$; oxidation states -2, +2, +4, +6. Hydride acidity: $H_2O < H_2S < H_2Se < H_2Te$.

Two key exceptions
Electron gain enthalpy of S is more negative than O (small O, e⁻-e⁻ repulsion). $O_2$ is paramagnetic (2 unpaired e⁻ in $\pi^*$); $O_3$ is diamagnetic.

Dioxygen and Oxides

ReactionEquation
$O_2$ lab prep$2KClO_3 \xrightarrow{MnO_2} 2KCl + 3O_2$
Peroxide + water$Na_2O_2 + 2H_2O \rightarrow 2NaOH + H_2O_2$
Superoxide + water$2KO_2 + 2H_2O \rightarrow 2KOH + H_2O_2 + O_2$
Oxide typeO stateExample
Normal oxide-2$Na_2O$
Peroxide-1$Na_2O_2$
Superoxide-1/2$KO_2$

Ozone

$$\boxed{3O_2 \xrightarrow{\text{silent electric discharge}} 2O_3 \qquad \Delta H = +142\ \text{kJ/mol}}$$
  • Structure: bent, $sp^2$, bond angle 117°, bond length 128 pm, resonance hybrid.
  • Detection: $3Hg + O_3 \rightarrow 3HgO$. Ozonolysis cleaves C=C.
  • O₃ bleaches permanently (oxidation); SO₂ bleaches temporarily (reduction).

Sulfur and H₂S

  • Allotropes: Rhombic ($\alpha$-S) $\rightleftharpoons$ Monoclinic ($\beta$-S) at transition 369 K; both are $S_8$ puckered rings.
ReactionEquation
$H_2S$ lab prep$FeS + 2HCl \rightarrow FeCl_2 + H_2S$
$H_2S$ reducing$H_2S + Cl_2 \rightarrow 2HCl + S$
With $SO_2$$2H_2S + SO_2 \rightarrow 3S + 2H_2O$
Black ppt (QA)$H_2S + CuSO_4 \rightarrow CuS\downarrow + H_2SO_4$
  • $H_2S$ structure: bent, angle 92°; more acidic than $H_2O$ ($K_{a1}\approx 10^{-7}$ vs $K_w = 10^{-14}$).

Oxides of Sulfur and Contact Process

$$\boxed{2SO_2 + O_2 \underset{V_2O_5}{\overset{450°C,\ 2\ atm}{\rightleftharpoons}} 2SO_3}$$
StepEquation
Burn S$S + O_2 \rightarrow SO_2$ (or $4FeS_2 + 11O_2 \rightarrow 2Fe_2O_3 + 8SO_2$)
Oxidation (key)$2SO_2 + O_2 \rightleftharpoons 2SO_3$
Absorption (NOT direct water)$SO_3 + H_2SO_4 \rightarrow H_2S_2O_7$
Dilution$H_2S_2O_7 + H_2O \rightarrow 2H_2SO_4$
$SO_2$ lab prep$Na_2SO_3 + H_2SO_4 \rightarrow Na_2SO_4 + H_2O + SO_2$
  • $SO_2$: bent, angle 119°, $sp^2$; $SO_3$: planar triangular, angle 120°, $sp^2$.

Sulfuric Acid

BehaviourEquation
Dehydration$C_{12}H_{22}O_{11} \xrightarrow{conc.\ H_2SO_4} 12C + 11H_2O$
Oxidation$Cu + 2H_2SO_4(conc) \rightarrow CuSO_4 + SO_2 + 2H_2O$
Oxidises HBr$2HBr + H_2SO_4(conc) \rightarrow Br_2 + SO_2 + 2H_2O$
Common trap - H₂SO₄
Conc. $H_2SO_4$ cannot prepare HBr / HI (it oxidises them to $Br_2$ / $I_2$); use non-oxidising $H_3PO_4$. Cold conc. $H_2SO_4$ passivates Fe and Al.

Group 17 - Halogens (F, Cl, Br, I, At)

Configuration $ns^2 np^5$; oxidation states -1, +1, +3, +5, +7 (F only -1).

TrendOrder
Oxidising power / reactivity$F_2 > Cl_2 > Br_2 > I_2$
Bond dissociation energy$Cl{-}Cl > Br{-}Br > F{-}F > I{-}I$
Electron gain enthalpy$Cl > F$ (F anomaly)
ElectronegativityF (4.0) > Cl (3.0) > Br (2.8) > I (2.5)
$$\boxed{\text{Displacement: more reactive halogen displaces less reactive: } Cl_2 + 2Br^- \rightarrow 2Cl^- + Br_2}$$

Chlorine and Bleaching Powder

ReactionEquation
$Cl_2$ lab prep$4HCl + MnO_2 \xrightarrow{\Delta} MnCl_2 + 2H_2O + Cl_2$
$Cl_2$ industrial (brine)$2NaCl + 2H_2O \xrightarrow{electrolysis} 2NaOH + Cl_2 + H_2$
With water (disproportionation)$Cl_2 + H_2O \rightleftharpoons HCl + HOCl$
Cold dil. NaOH (+1)$Cl_2 + 2NaOH \rightarrow NaCl + NaOCl + H_2O$
Hot conc. NaOH (+5)$3Cl_2 + 6NaOH \rightarrow 5NaCl + NaClO_3 + 3H_2O$
Bleaching powder$Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$
  • Bleaching powder $\approx CaOCl_2$ (chlorinated lime); $CaOCl_2 + 2HCl \rightarrow CaCl_2 + H_2O + Cl_2$.

HF and Hydrogen Halides

PropertyHFHClHBrHI
Boiling point293 K189 K206 K238 K
Bond strength (kJ/mol)574431366299
Acidic strengthWeakest$\rightarrow$$\rightarrow$Strongest
Reducing powerNoneWeakModerateStrong
$$\boxed{\text{Acidic strength: } HF < HCl < HBr < HI}$$
PrepEquation
HF / HCl$NaX + H_2SO_4(conc) \rightarrow NaHSO_4 + HX$
HBr / HI (use $H_3PO_4$)$NaBr + H_3PO_4 \rightarrow NaH_2PO_4 + HBr$
F₂ (only electrolysis)$2KHF_2 \xrightarrow{electrolysis} 2KF + H_2 + F_2$
HF + glass$SiO_2 + 4HF \rightarrow SiF_4 + 2H_2O$
HF paradox
HF is the weakest acid among HX (extensive H-bonding makes ionisation difficult) despite F being most electronegative. HF is stored in wax/plastic, never glass.

Iodine and Interhalogens

ReactionEquation
Iodometry$I_2 + 2Na_2S_2O_3 \rightarrow 2NaI + Na_2S_4O_6$
Starch test$Starch + I_2 \rightarrow$ blue-black complex
Triiodide$I_2 + I^- \rightarrow I_3^-$

Interhalogens $XX'_n$ ($n = 1,3,5,7$); X is the larger, less electronegative central atom.

CompoundHybridisationShape
$ClF_3$$sp^3d$T-shaped
$IF_5$$sp^3d^2$Square pyramidal
$IF_7$$sp^3d^3$Pentagonal bipyramidal

Group 18 - Noble Gases (He, Ne, Ar, Kr, Xe, Rn)

Configuration $ns^2 np^6$ (He: $1s^2$); positive electron gain enthalpy (all). Reactivity: $Xe > Kr$ only.

  • IE order: He (2372) > Ne (2081) > Ar (1521) > Kr (1351) > Xe (1170) kJ/mol.
  • Bartlett (1962): first noble gas compound $Xe^+[PtF_6]^-$ (since IE of Xe $\approx$ IE of $O_2$, 1170 $\approx$ 1175).

Xenon Fluorides

$$\boxed{Xe + nF_2 \rightarrow XeF_{2n}} \quad (XeF_2: 673K,\ 1{:}1;\ XeF_4: 673K, 6\ atm, 1{:}2;\ XeF_6: 573K, 60\ atm, 1{:}5)$$
CompoundHybridisationShapeLone pairs
$XeF_2$$sp^3d$Linear3
$XeF_4$$sp^3d^2$Square planar2
$XeF_6$$sp^3d^3$Distorted octahedral1
$XeO_3$$sp^3$Trigonal pyramidal1
$XeOF_4$$sp^3d^2$Square pyramidal1
$XeO_4$$sp^3$Tetrahedral0
HydrolysisEquation
$XeF_2$$2XeF_2 + 2H_2O \rightarrow 2Xe + 4HF + O_2$
$XeF_4$$6XeF_4 + 12H_2O \rightarrow 4Xe + 2XeO_3 + 24HF + 3O_2$
$XeF_6$ (complete)$XeF_6 + 3H_2O \rightarrow XeO_3 + 6HF$
$XeF_6$ (partial)$XeF_6 + H_2O \rightarrow XeOF_4 + 2HF$
  • Only F forms stable Xe compounds (most electronegative). $XeO_3$ and $XeO_4$ are explosive.

Oxoacids - Acidity and Basicity Rules

The three master rules

More O atoms / higher oxidation state $\rightarrow$ stronger acid (same central atom).

Smaller / more electronegative central atom $\rightarrow$ stronger acid (same number of O).

Basicity = number of OH groups only - a P-H bond does NOT ionise.

Halogen Oxoacids (Cl example)

AcidCl state$pK_a$Strength
HOCl+17.5Weakest
$HClO_2$+32Weak
$HClO_3$+5-1Strong
$HClO_4$+7-10Strongest
$$\boxed{\text{Acidity: } HOCl < HClO_2 < HClO_3 < HClO_4 \qquad \text{Oxidising power: reverse}}$$
  • $HClO_4$ is the strongest common acid. Periodic acid exists as $HIO_4$ (meta) and $H_5IO_6$ (para, pentabasic, cleaves 1,2-diols).

Nitrogen Oxoacids

AcidN state$pK_a$Note
$H_2N_2O_2$+1-Hyponitrous, unstable
$HNO_2$+33.3Both oxidising & reducing; $3HNO_2 \rightarrow HNO_3 + 2NO + H_2O$
$HNO_3$+5-1.4Strong acid, only oxidising

Sulfur Oxoacids

AcidFormulaS stateBasicity
Sulfurous$H_2SO_3$+4Dibasic (unstable)
Sulfuric$H_2SO_4$+6Dibasic (strong)
Thiosulfuric$H_2S_2O_3$+2 (avg)Dibasic
Peroxodisulfuric$H_2S_2O_8$+6Dibasic (peroxy -O-O-)
Pyrosulfuric (oleum)$H_2S_2O_7$+6Dibasic
  • Sodium thiosulfate “hypo” $Na_2S_2O_3{\cdot}5H_2O$: $Na_2SO_3 + S \rightarrow Na_2S_2O_3$; photo fixer $AgBr + 2Na_2S_2O_3 \rightarrow Na_3[Ag(S_2O_3)_2] + NaBr$.

Phosphorus Oxoacids

$$\boxed{\text{Basicity counts OH groups: } H_3PO_2 \text{ (mono)},\ H_3PO_3 \text{ (di)},\ H_3PO_4 \text{ (tri)}}$$
AcidFormulaP stateP-H bondsBasicityReducing
Hypophosphorous$H_3PO_2$+12MonobasicStrong
Phosphorous$H_3PO_3$+31DibasicModerate
Orthophosphoric$H_3PO_4$+50TribasicNone
Pyrophosphoric$H_4P_2O_7$+50TetrabasicNone
Metaphosphoric$HPO_3$+50Monobasic (per unit)None
  • Disproportionation on heating: $4H_3PO_3 \rightarrow 3H_3PO_4 + PH_3$ and $3H_3PO_2 \rightarrow 2H_3PO_3 + PH_3$.

High-Yield Memory Map

graph TD
    A[p-Block Groups 13-18] --> B[13: B, Al - +3, inert pair in Tl]
    A --> C[14: C, Si - +4/+2, catenation C>>Pb]
    A --> D[15: N, P - -3/+3/+5, Haber & Ostwald]
    A --> E[16: O, S - -2 to +6, Contact process]
    A --> F[17: Halogens - F only -1, oxidising F2>I2]
    A --> G[18: Noble gases - Xe fluorides/oxides]
    D --> H[Oxoacids: basicity = OH count]
    E --> H
    F --> H

One-Glance Trap List

Last-minute trap sweep

$H_3BO_3$ = Lewis acid (accepts $OH^-$), monobasic.

$AlCl_3$ = $Al_2Cl_6$ dimer.

$SiCl_4$ hydrolyses, $CCl_4$ does not (d-orbitals).

CO neutral, $CO_2$ acidic; graphite is $sp^2$ (conductor).

Dilute $HNO_3 \rightarrow$ NO; conc. $\rightarrow NO_2$; passivates only Fe/Al/Cr; aqua regia 3:1.

$H_3PO_3$ dibasic (not tribasic); $O_2$ paramagnetic; $H_2S$ more acidic than $H_2O$.

HF weakest HX acid (H-bonding); F shows only -1; bond energy $Cl_2 > F_2$.

$XeF_2$ linear, $XeF_4$ square planar; noble gases have positive $\Delta_{eg}H$.

Oxoacid acidity: $HClO_4 > HOCl$, but oxidising power: $HOCl > HClO_4$.

Related: Group 13 | Group 14 | Group 15 | Group 16 | Group 17 | Group 18 | Oxoacids

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