Group 15 elements
Elements:
N, P → Non-metals
As, Sb → Metalloids
Bi → Metal
(Pnictogens)
Group 15 Oxidation states
Valence config: ns² np³
Common O.S.: −3, +3, +5
3 covalent + 1 coordinate (dative) bond
+3 → Ground state (ns² np³) → 3 unpaired e⁻ → trivalent
+5 → Excited state (ns¹ np³ nd¹) → pentavalent
(N: no d-orbitals → no octet expansion)
Group 15 Trends
1.Apart from common O.S.:
N → +1, +2, +4 (oxides & oxyacids)
P → +1, +4 (oxyacids)
- Intermediate O.S. (between −3 & +5) → tendency to undergo disproportionation
- Down the group:
Stability of +5 ↓ - decreases
Stability of +3 ↑ - increases (inert pair effect)
Group 16 elements
O, S → Non-metals
Se, Te → Metalloids
Po → Metal
(Chalcogens)
Group 16 Oxidation states
Valence config: ns² np⁴
Common O.S.: −2, +2, +4, +6
−2 → Gain 2e⁻ → oxide/sulfide formation
+2 → Ground state (ns² np⁴) → 2 unpaired e⁻ → divalent
+4 → Excited state 1 → 4 unpaired e⁻ → tetravalent
+6 → Excited state 2 → 6 unpaired e⁻ → hexavalent
(O: no d-orbitals → cannot expand octet → max O.S. = −2)
Apart from common OS
O → −1 (peroxides), −½ (superoxides), +1, +2 (in fluorides)
S, Se, Te → +2, +4 (oxides & oxyacids)
Group 16 trends
- Apart from common O.S.:
O → −1 (peroxides), −½ (superoxides), +1, +2 (in fluorides)
S, Se, Te → +2, +4 (oxides & oxyacids) - Intermediate O.S. (between −2 & +6) → tendency to undergo disproportionation
- Down the group:
Stability of +6 ↓
Stability of +4 ↑ (inert pair effect)
Group 17 elements
Elements:
F, Cl → Non-metals
Br → Non-metal (liquid)
I → Non-metal (solid)
Halogens
Group 17 OS
Valence config: ns² np⁵
Ground state: ns² np⁵ → −1, +1
ES₁:ns² np⁴ nd¹ → +3
ES₂:ns² np³ nd² → +5
ES₃:ns¹ np³ nd³ → +7
F → no d-orbitals → only −1 (does not show positive O.S.)
Group 17 trends
Most common state is -1, making them act as oxidising agents
Oxidising power: F₂ > Cl₂ > Br₂ > I₂
Group 18
Elements:
He, Ne, Ar, Kr, Xe, Rn
Valence config:
He → 1s²
Others → ns² np⁶ (complete octet)
Common O.S.:
0 (generally inert)
Trends in p-block Hydrides
G15 → EH₃
G16 → EH₂
G17 → EH
Down the group:
Bond length ↑
Bond Energy/Stability↓
Basic Strength ∝ charge density ↓
Reducing power ↑
Bond angle ↓
Trends in p-block oxides
- Acid Strength Pattern:
Higher oxidation state oxide → more acidic
Example logic:
E₂O₅ > E₂O₃ (acidic strength)
Reason: higher positive charge → stronger electron withdrawal → stronger acidity
- Nature Classification Pattern:
Non-metal oxides → Acidic
Metalloid oxides → Amphoteric
Metal oxides → Basic
Nitrogen Trihalides
Formula: NX₃
NF₃ → Stable
NCl₃ → Explosive
NBr₃, NI₃ → Very unstable
Polyhalides
Formed by combination of halide ion + halogen
General form: X₃⁻, X₅⁻, X₇⁻
Example: I₂ + I⁻ → I₃⁻
Structure: I₃⁻ → Linear
Stability: I⁻ forms polyhalides most readily
(F⁻ does not form polyhalides)
Pseudohalides
Polyatomic ions that behave like halide ions (X⁻), commonly with nitrogen
Examples:
CN⁻ (cyanide)
N₃⁻ (azide)
SCN⁻ (thiocyanate)
Nitrogen oxides
Oxide | O.S. | Physical State | Colour
N₂O | +1 | Gas | Colourless
NO | +2 | Gas | Colourless
NO₂ | +4 | Gas | Brown
N₂O₃ | +3 | Liquid | Blue
N₂O₄ | +4 | Liquid/Solid | Colourless
N₂O₅ | +5 | Solid/Solid | Colourless
N₂O₄ ⇌ 2NO₂ | Heat ⇌ Cool
NO + NO₂ ⇌ N₂O₃ | Low temperature
Nitrogen Oxyacids
Molecules with N,H,O
Nitrous: +1(Hypo), +3
Nitric: +5
Phosphorus Oxyacids
Molecules with P, H, O
Phosphorus: +1(Hypo), +3(ortho)
Phosphoric acid: +4(Hypo), +5(ortho)
2H₃PO₄ –Δ–> H₄P₂O₇+H2O
Pyrophosphoric acid
2H₃PO₃ –Δ–> H₄P₂O₅+H2O
Pyrophosphorous acid
nH₃PO₄ → H₄P₂O₇ → (HPO₃)n
Phosphorus Oxides
P₄Oₓ
x =
1-5 unstable
6-10 known
P₄O₆ → Phosphorus(III) oxide (yellow, P in +3 oxidation state)
P₄O₁₀ → Phosphorus(V) oxide (white, P in +5 oxidation state)
Sulphur Oxides
SO₂: L/G → molecular, Solid → molecular, no polymer
SO₃: L/G → molecular, Solid → polymer
α, β → linear
γ → cyclic/molecular
Sulphur Oxyacids
a) Sulfurous acids (S in +2/+4):
H₂SO₃ – Sulfurous acid (+4)
H₂S₂O₂ – Thiosulfurous acid (+2/+2)
H₂S₂O₅ – Pyrosulfurous acid (+4)
b) Sulfuric acids (S in +6):
H₂SO₄ – Sulfuric acid
H₂S₂O₃ – Thiosulfuric acid
H₂S₂O₈ – Peroxodisulfuric acid (Marshall’s acid)
Adding –O–O– groups(peroxy acids) gives:
H₂SO₅ – Peroxomonosulfuric acid (Caro’s acid)
H₂S₂O₈ – Peroxodisulfuric acid (Marshall’s acid)
c) Thionous acids (S in lower oxidation states, rare):
General formula: H₂SₙO₄, n = 2, 3, 4
Halogen Oxyacids
Halous: +1(Hypo), +3
Halic: +5, +7(per)
Basicity of an oxyacid
refers to the number of OH group directly attached to the central atom
Prep of H2SO4
oxidization of S/roasting of sulphide ores
S + O2 –> SO2
SO2 + O2 –> SO3
SO3 + H2O –> H2SO4
