Definitions [16]
Definition: Acidic Oxide
An oxide which dissolves in water to give an acid or reacts with a base to form salt is called an acidic oxide.
Definition: Basic Oxide
An oxide which dissolves in water to give a base or reacts with an acid to form salt is called a basic oxide.
Definition: Amphoteric Oxide
An oxide which reacts with both acids and bases to form salt is called an amphoteric oxide.
Definition: Neutral Oxide
An oxide which is neither acidic nor basic is called a neutral oxide.
Definition: Ozonosphere
The layer of ozone in the upper atmosphere that absorbs harmful ultraviolet radiation is called the ozone layer (ozonosphere).
Definition: Ozone Depletion
The thinning of ozone layer in the upper atmosphere is called ozone depletion.
Definition: Oxides
Binary compounds of oxygen with another element are called oxides.
Definition: Aqua Regia
A mixture of concentrated HCl and concentrated HNO₃ in the ratio 3:1 is called aqua regia.
Definition: Hydrogen Halide
A compound formed by reaction of hydrogen with halogen is called a hydrogen halide.
Definition: Noble Gases
Group 18 elements (He, Ne, Ar, Kr, Xe, Rn) having completely filled valence shell (ns²np⁶) are called noble gases.
Definition: Allotropy
The existence of an element in two or more different physical forms in the same physical state is called allotropy.
Definition: Oxoacids
Acids which contain oxygen along with another element are called oxoacids.
Example:
H₂SO₄, HClO₄
Definition: Hydrogen Halides
Compounds formed by reaction of halogens with hydrogen are called hydrogen halides.
General formula:
H₂ + X₂ → 2HX
(X = F, Cl, Br, I)
Definition: Paramagnetism
Substances having unpaired electrons and attracted by magnetic field show paramagnetism.
O₂ is paramagnetic.
Definition: Chalcogens
Group 16 elements (O, S, Se, Te, Po) are called chalcogens or ore forming elements.
Definition: Halogens
Group 17 elements (F, Cl, Br, I, At) are called halogens, meaning salt-producing elements.
Key Points
Key Points: Electronic Configuration
| Group | Name | General Configuration | Valence e⁻ | Tendency | Key Property | Example | Special Note |
|---|---|---|---|---|---|---|---|
| 16 | Chalcogens | ns² np⁴ | 6 | Gain 2 e⁻ | Moderately reactive | O→2s²2p⁴ S→3s²3p⁴ |
Incomplete octet |
| 17 | Halogens | ns² np⁵ | 7 | Gain 1 e⁻ | Highly reactive | Cl→3s²3p⁵ Br→4s²4p⁵ | Very high electron affinity |
| 18 | Noble gases | ns² np⁶ (except He) | 8 | Stable (no gain/loss) | Inert / least reactive | Ne→2s²2p⁶ Ar→3s²3p⁶ | He = 1s² |
Key Points: Atomic and Physical Properties
Atomic Properties:
| Property | Group 16 | Group 17 | Group 18 |
|---|---|---|---|
| Atomic radius | Increases down the group, decreases across the period | Increases down the group, decreases across the period | Increases down the group, decreases across the period |
| Ionisation energy | Decreases down the group, increases across the period | High; decreases down the group | Very high |
| Electronegativity | Moderate; decreases down the group | Very high; decreases down the group | Nearly zero |
| Electron gain enthalpy | Oxygen less negative than sulphur | Fluorine less negative than chlorine | Positive values |
| General trend | Tendency to gain 2 electrons | Tendency to gain 1 electron | Stable configuration |
Physical Properties:
| Property | Group 16 | Group 17 | Group 18 |
|---|---|---|---|
| Physical state | Oxygen is gas; others are solids | Fluorine and chlorine are gases, bromine is a liquid, iodine is a solid | All are gases |
| Nature | Non-metals to metal down the group | Non-metals | Inert gases |
| Reactivity | Moderate | Very high | Very low |
| Melting and boiling point | Increase down the group | Increase down the group | Very low values |
| Special features | Show allotropy | Show characteristic colours and high reactivity | Monoatomic and chemically inert |
| Examples | O, S, Se, Te, Po | F, Cl, Br, I, At | He, Ne, Ar, Kr, Xe, Rn |
Key Points: Anomalous Behaviour of Oxygen
Reasons
- Small atomic size
- High electronegativity and ionisation energy
- Absence of d-orbitals
Important Properties
| Property | Oxygen |
|---|---|
| Nature | Diatomic gas (O₂) |
| Magnetic behaviour | Paramagnetic |
| Oxidation state | Mainly −2 |
| Hydride | H₂O is liquid at room temperature |
| Covalency | Usually 2 |
Key Points: Anomalous Behaviour of Fluorine
Reasons
- Small atomic size
- Very high electronegativity
- Absence of d-orbitals
- Low F–F bond dissociation energy
| Property | Fluorine |
|---|---|
| Oxidation state | Only −1 (does not show + states) |
| Hydride | HF is liquid (others are gases) |
| Nature | Form more ionic compounds |
| Oxyacids | Forms only one oxyacid (HOF) |
Key Points: Chemical Properties
Oxidation States:
| Group | Common Oxidation States |
|---|---|
| 16 | −2, +2, +4, +6 |
| 17 | −1, +1, +3, +5, +7 |
| 18 | 0 (Xe shows +2, +4, +6) |
Reactivity with Hydrogen:
| Property | Group 16 | Group 17 |
|---|---|---|
| Acidic strength | H₂O < H₂S < H₂Se < H₂Te | HF < HCl < HBr < HI |
| Thermal stability | H₂O > H₂S > H₂Se > H₂Te | HF > HCl > HBr > HI |
| Reducing power | H₂S < H₂Se < H₂Te | Increases down group |
Reactivity with Oxygen:
| Group | Key Points |
|---|---|
| 16 | Forms EO₂, EO₃; acidic oxides; act as oxidising & reducing agents |
| 17 | Forms oxides (Cl₂O, Cl₂O₇ etc.); strong oxidising agents |
Reactivity with Halogens:
| Group | Key Points |
|---|---|
| 16 | Forms halides (EX₂, EX₄, EX₆) |
| 17 | Forms interhalogen compounds |
| 18 | Xe, Kr form fluorides (XeF₂, XeF₄, XeF₆) |
Reactivity with Metals:
| Group | Key Points |
|---|---|
| 16 | Forms metal oxides/sulphides (MgSe, CuS) |
| 17 | Forms salts (NaCl, MgBr₂) |
| 18 | No reaction (inert) |
Allotropy:
| Element | Allotropes |
|---|---|
| Oxygen | O₂, O₃ |
| Sulfur | Rhombic, Monoclinic |
| Selenium | Red, Grey |
| Tellurium | Crystalline, Amorphous |
Key Points: Oxygen and Compounds of Oxygen
oxygen (O₂)
Preparation:
- Heating potassium chlorate:
KClO₃ → O₂ (MnO₂ catalyst) - Electrolysis of water
Chemical Properties:
- With metals → metal oxides
2Ca + O₂ → 2CaO
4Al + 3O₂ → 2Al₂O₃ - With non-metals → non-metal oxides
C + O₂ → CO₂
P₄ + 5O₂ → P₄O₁₀ - With HCl:
4HCl + O₂ → 2H₂O + 2Cl₂ - Oxidation reaction:
2SO₂ + O₂ → 2SO₃ (V₂O₅ catalyst)
Types of Oxides:
| Type | Nature | Examples |
|---|---|---|
| Acidic | Form acids in water | SO₂, CO₂, N₂O₅ |
| Basic | Form bases in water | Na₂O, CaO, BaO |
| Amphoteric | Both acidic & basic | Al₂O₃ |
| Neutral | Neither acidic nor basic | CO, NO, N₂O |
Key Points: Chemical Properties of Groups 16, 17 and 18
| Property | Group 16 (Chalcogens) | Group 17 (Halogens) | Group 18 (Noble Gases) |
|---|---|---|---|
| Oxidation States | Show –2 and +2 commonly; also +4 and +6 (except O mainly –2). Stability of +6 decreases down group; +4 increases down group. | All show –1; Cl, Br, I also show +1, +3, +5, +7. Fluorine shows only –1. | Generally 0; Xe shows +2, +4, +6 in compounds like XeF₂, XeF₄, XeF₆, XeO₃, XeOF₄. |
| Reactivity with Hydrogen | Form hydrides H₂E (H₂O, H₂S, etc.). Acidic character increases down group; thermal stability decreases. | Form hydrogen halides HX (HF, HCl, HBr, HI). Acid strength: HF < HCl < HBr < HI. | Chemically inert towards hydrogen. |
| Reactivity with Oxygen | Form oxides EO₂ and EO₃. Mostly acidic; dissolve in water to form acids (e.g., SO₂ + H₂O → H₂SO₃). | Form many oxides; mostly unstable. Higher oxides more stable. | Do not directly react with oxygen. |
| Reactivity with Halogens | Form EX₆, EX₄, EX₂ (e.g., SF₆, SeF₄). Stability decreases F > Cl > Br > I. | Form interhalogen compounds (XX', XX'₃, XX'₅, XX'₇). | React with fluorine (e.g., Xe + F₂ → XeF₂). |
| Reactivity with Metals | React to form compounds (e.g., 4Al + 3O₂ → 2Al₂O₃). | React to form metal halides (e.g., 2Na + Cl₂ → 2NaCl). | Do not directly react with metals. |
Key Points: Atomic and Physical Properties of Groups 16, 17 and 18
| Property | Group 16 (Chalcogens) | Group 17 (Halogens) | Group 18 (Noble Gases) |
|---|---|---|---|
| Valence Shell Configuration | ns²np⁴ | ns²np⁵ | ns²np⁶ |
| Atomic Radius | Increases down the group | Increases down the group | Increases down the group |
| Ionisation Enthalpy | High; decreases down the group | Very high; decreases down the group | Very high; decreases down the group |
| Electronegativity | Decreases down the group; O highest | Decreases down the group; F highest | Almost zero / negligible |
| Electron Gain Enthalpy | Becomes less negative down the group | Highly negative; becomes less negative down the group | Positive (no tendency to gain electron) |
| Physical State | O₂ gas; others solids | F₂, Cl₂ gases; Br₂ liquid; I₂ solid | Monoatomic gases |
| Melting & Boiling Points | Increase down the group | Increase down the group | Very low; increase slightly down the group |
| Special Feature | Show allotropy | Highly reactive | Chemically inert |
Key Points: Anomalous Behaviour of Oxygen and Fluorine
| Property | Oxygen (Group 16) | Fluorine (Group 17) |
|---|---|---|
| Atomicity | Exists as diatomic molecule (O₂); others are polyatomic (e.g., S₈). | Exists as diatomic molecule (F₂) like other halogens. |
| Magnetic Nature | Paramagnetic in nature. | Diamagnetic in nature. |
| Oxidation States | Shows –2 (main), –1 and +2; does not show higher oxidation states. | Shows only –1 oxidation state. |
| Nature of Hydrides | H₂O is liquid due to hydrogen bonding. | HF is liquid due to strong hydrogen bonding. |
| Oxoacids Formation | Forms several oxides but limited oxidation states. | Forms only one oxoacid (HOF). |
| Reason for Anomalous Behaviour | Small size, high electronegativity, absence of d-orbitals. | Small size, high electronegativity, absence of d-orbitals, low F–F bond dissociation enthalpy. |
Important Questions [37]
- Write the chemical composition of cryolite.
- Elements of group 16 have lower ionization enthalpy values compared to those of group 15 elements. Explain why?
- Explain the trends in the following atomic properties of group 16 elements: Electron gain enthalpy
- Explain the trends in the following atomic properties of group 16 elements: Electronegativity
- Explain the trends in the following atomic properties of group 16 elements: Ionisation enthalpy
- Explain the trends in the following atomic properties of group 16 elements: Atomic radii
- Describe anomalous behaviour of oxygen as compared with other elements of group 16 with reference to
- Explain anomalous behaviour of oxygen in group 16 with respect to: Atomicity Magnetic property Oxidation state
- Describe Anomalous Behaviour of Fluorine with the Other Elements of Group 17 Wilh Reference to
- Write Any ‘Four Points’ of Difference Between Fluorine and Other Halogens.
- Arrange the following in the increasing order of the property mentioned: HF, HCl, HBr, HI (thermal stability)
- What is the action of selenium on magnesium metal?
- Arrange the following in the increasing order of the property mentioned: HOCl, HClOA2, HClOA3, HClOA4 (acidic strength)
- Draw the structure of chloric acid.
- Draw the structure of the following compound: Peroxy disulphuric acid
- Draw the structure of chlorous acid.
- Draw the structure of peroxymonosulphuric acid.
- Ozone layer is depleted by ______.
- Give reason: Bleaching action of ozone is also called dry bleach.
- Write any two characteristics of interhalogen compounds.
- How is dioxygen prepared in the laboratory from KClO3?
- What are interhalogen compounds?
- What is the Action of Chlorine on : Cs2
- Write Any Two Uses of Chlorine
- Which of the Following Compounds of Chlorine is Used as Refrigerant?
- Arrange the following oxyacids of chlorine - HClO, HClO2, HClO3, and HClO4 with respect to increasing order of oxidizing power.
- What is the Action of Chlorine (Cl) on the Following: Potassium Bromide Solution
- What is the Action of Chlorine (Cl) on the Following: Hot and Concentrated Caustic Soda
- What is the Action of Chlorine (Cl) on the Following: Cold and Dilute Caustic Soda
- What Happens When Thin Copper Leaves Are Thrown in Jar Containing Chlorine?
- Arrange the Following Oxyacids of Chlorine – Hclo, Hclo2, Hclo3, and Hclo4 with Respect To Increasing Order of Thermal Stability.
- Write the chemical reaction,when chlorine reacts with dry slaked lime.
- Answer the following. What is the action of chlorine on Excess NH3.
- Write two uses of neon.
- Complete the following equation: XeF𝐴2+H𝐴2O
- Write Electronic Configuration and Two Uses of Neon. (Z = 10)
- Write the Electronic Configuration of the Following Element: Krypton (Z = 36)
Concepts [11]
- Occurrence of Elements of Groups 16, 17 and 18
- Electronic Configuration of Elements of Group 16, 17 and 18
- Atomic and Physical Properties of Elements of Group 16, 17 and 18
- Anomalous Behaviour of Oxygen
- Anomalous Behaviour of Fluorine
- Chemical Properties of Elements of Groups 16, 17 and 18
- Oxoacids
- Oxygen and Compounds of Oxygen
- Chlorine
- Group 18 Elements - The Noble gas Family
- Overview of Elements of Groups 16, 17 and 18
