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Short Notes: p-Block Elements
Group 15 Elements (Nitrogen Family)
| Element | N | P | As | Sb | Bi |
|---|---|---|---|---|---|
| Electronic Config | ns2np3 | ||||
| Oxidation States | -3, +3, +5 (stability of +5 decreases down group) | ||||
Properties of Group 15
- Atomic/Ionic size: Increases down the group
- Ionization enthalpy: Decreases down the group
- Electronegativity: Decreases down the group
- Metallic character: Increases (N, P = non-metal; As, Sb = metalloid; Bi = metal)
- Bond dissociation enthalpy: N2 (triple bond) > P4 (single bonds)
Ammonia
- Preparation (Haber process): N2 + 3H2 ⇌ 2NH3 (450-500°C, 200 atm, Fe catalyst)
- Structure: Pyramidal, sp3 hybridization, bond angle 107°
- Properties: Colorless, pungent smell, highly soluble in water, basic
- Reactions:
- With HCl: NH3 + HCl → NH4Cl (white fumes)
- With O2: 4NH3 + 5O2 → 4NO + 6H2O (catalytic oxidation)
Oxides of Nitrogen
| Formula | Name | Color | Nature |
|---|---|---|---|
| N2O | Nitrous oxide | Colorless | Neutral |
| NO | Nitric oxide | Colorless | Neutral |
| N2O3 | Dinitrogen trioxide | Blue | Acidic |
| NO2 | Nitrogen dioxide | Brown | Acidic |
| N2O5 | Dinitrogen pentoxide | Colorless | Acidic |
Nitric Acid
- Ostwald Process:
- 4NH3 + 5O2 → 4NO + 6H2O
- 2NO + O2 → 2NO2
- 4NO2 + 2H2O + O2 → 4HNO3
- Reactions with metals:
- Cu + 8HNO3(conc.) → 3Cu(NO3)2 + 2NO + 4H2O
- 3Cu + 8HNO3(dil.) → 3Cu(NO3)2 + 2NO + 4H2O
- Aqua regia: 3:1 conc. HCl:HNO3 dissolves gold and platinum
Phosphorus Allotropes
- White phosphorus (P4):
- Tetrahedral structure, soft, waxy, poisonous
- Stored under water, ignites at 30°C
- Red phosphorus:
- Polymeric, non-poisonous, stable
- Obtained by heating white P at 573K
Group 16 Elements (Oxygen Family)
| Property | Trend |
|---|---|
| Electronic Config | ns2np4 |
| Oxidation States | -2, +2, +4, +6 |
| Atomic size | Increases down group |
| Electronegativity | Decreases (O > S > Se > Te > Po) |
Ozone
- Preparation: 3O2 → 2O3 (silent electric discharge)
- Structure: Bent, resonance hybrid, bond angle 117°
- Properties: Pale blue gas, pungent smell, powerful oxidizing agent
- Reactions:
- 2KI + H2O + O3 → 2KOH + I2 + O2
- PbS + 4O3 → PbSO4 + 4O2
- Ozone layer depletion: CFCs release Cl radicals that catalyze O3 decomposition
Sulphur Dioxide
- Preparation: S + O2 → SO2 or Cu + 2H2SO4(conc.) → CuSO4 + SO2 + 2H2O
- Structure: Bent, sp2 hybridization, bond angle ~119°
- Properties: Colorless, pungent smell, reducing agent, bleaching agent
Sulphuric Acid
- Contact Process:
- S + O2 → SO2
- 2SO2 + O2 ⇌ 2SO3 (V2O5 catalyst, 450°C)
- SO3 + H2SO4 → H2S2O7 (oleum)
- H2S2O7 + H2O → 2H2SO4
- Properties: Viscous, oily liquid, strong dibasic acid, dehydrating agent, oxidizing agent
Group 17 Elements (Halogens)
| Element | F | Cl | Br | I |
|---|---|---|---|---|
| Electronic Config | ns2np5 | |||
| Physical State | Gas | Gas | Liquid | Solid |
| Color | Pale yellow | Greenish yellow | Reddish brown | Violet |
| Oxidation States | -1 only | -1, +1, +3, +5, +7 | ||
Properties of Halogens
- Electronegativity: F > Cl > Br > I (F is most electronegative element)
- Oxidizing power: F2 > Cl2 > Br2 > I2
- Bond dissociation enthalpy: Cl2 > Br2 > F2 > I2
- Reactivity: F > Cl > Br > I
Chlorine
- Deacon's Process: 4HCl + O2 → 2Cl2 + 2H2O (CuCl2 catalyst, 450°C)
- Electrolytic: 2NaCl + 2H2O → 2NaOH + Cl2 + H2
- Reactions:
- With NaOH (cold): Cl2 + 2NaOH → NaCl + NaClO + H2O
- With NaOH (hot): 3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O
- With slaked lime: 2Ca(OH)2 + 2Cl2 → Ca(OCl)2 + CaCl2 + 2H2O (bleaching powder)
Hydrogen Halides
| Property | HF | HCl | HBr | HI |
|---|---|---|---|---|
| Thermal Stability | Decreases (HF > HCl > HBr > HI) | |||
| Acidic Strength | Increases (HF < HCl < HBr < HI) | |||
| Reducing Character | Increases (HF < HCl < HBr < HI) | |||
| Boiling Point | Highest (H-bonding) | Increases with size | ||
Interhalogen Compounds
- Compounds between two different halogens
- Types: XX', XX'3, XX'5, XX'7
- Examples: ClF3, BrF5, IF7, ICl
- More reactive than halogens (except F2)
Group 18 Elements (Noble Gases)
| Element | He | Ne | Ar | Kr | Xe | Rn |
|---|---|---|---|---|---|---|
| Electronic Config | 1s2 | ns2np6 | ||||
| Boiling Point | Increases down group (He lowest) | |||||
Xenon Compounds
- XeF2: Linear structure
- XeF4: Square planar structure
- XeF6: Distorted octahedral
- XeO3: Pyramidal structure
- XeOF4: Square pyramidal
- Preparation: Xe + F2 → XeF2, XeF4, XeF6 (different conditions)
NEET Focus:
- Trends in groups 15, 16, 17, 18
- Preparation and properties of NH3, HNO3, H2SO4
- Oxides of nitrogen and sulphur
- Interhalogen compounds structures
- Noble gas compounds (Xe compounds)
- Acidic strength and reducing character of hydrogen halides
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FAQs on Short Notes: p-Block Elements
| 1. What are p-block elements? |  |
Ans. p-block elements are a group of elements in the periodic table that have their outermost electrons in the p orbital. This block includes groups 13 to 18, encompassing a diverse range of elements such as boron, carbon, nitrogen, oxygen, fluorine, and noble gases. They exhibit varying properties and play significant roles in chemical reactions and compounds.
| 2. What are the general properties of p-block elements? | |
Ans. The general properties of p-block elements include a wide range of electronegativities, ionisation energies, and atomic radii. These elements can exist in multiple oxidation states and form covalent bonds. They also have varying physical states; for example, elements like carbon and phosphorus are solids, while chlorine and argon are gases at room temperature. Additionally, p-block elements can form both ionic and covalent compounds.
| 3. How do the oxidation states of p-block elements vary? | |
Ans. The oxidation states of p-block elements can vary significantly, often depending on the group they belong to. For instance, elements in group 13 typically exhibit a +3 oxidation state, while those in group 14 can display oxidation states ranging from +4 to -4. As we move across the p-block from left to right, the tendency to show higher oxidation states increases due to greater electronegativity and smaller atomic radii.
| 4. What role do p-block elements play in biological systems? | |
Ans. P-block elements are crucial in biological systems. For example, nitrogen (from group 15) is essential for the formation of amino acids and nucleic acids. Oxygen (from group 16) is vital for respiration in living organisms. Carbon (from group 14) is the backbone of all organic molecules. Additionally, elements like phosphorus and sulphur are key components of ATP and proteins, respectively, highlighting their importance in life processes.
| 5. What are some common uses of p-block elements? | |
Ans. P-block elements have various applications in everyday life and industry. For example, aluminium (from group 13) is widely used in construction and packaging due to its lightweight and corrosion-resistant properties. Silicon (from group 14) is fundamental in the electronics industry for making semiconductors. Chlorine (from group 17) is used for water purification and in the production of plastics. Each of these elements contributes significantly to technological advancements and environmental applications.
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