Chemistry eBook – Group Elements & Halogens
Chemistry eBook – Group 1, Halogens & Transition Elements
1. Multiple Choice Questions
Which halogen will have the least reactivity with alkaline earth metals?
Options: (a) Fluorine (b) Iodine ✓ (c) Chlorine (d) Bromine
Explanation: Iodine has the largest atomic size and weakest ability to gain electrons, hence least reactive.
Which compound do you expect to be coloured?
Options: (a) MgCl₂ (b) NaCl (c) KCl (d) NiCl₂ ✓
Nickel salts show colour due to d–d transitions.
In which element there exists the strongest forces of attraction between atoms?
Options: (a) Mg ✓ (b) Ca (c) Sr (d) Ba
Mg has smallest size and strongest metallic bonding.
Elements of which group are all coloured?
Options: (a) Group 1 (b) Group 6 ✓ (c) Group 17 (d) Group 18
Group 6 transition metals form coloured compounds due to unpaired d-electrons.
Which halogen acid is unstable at room temperature?
Options: (a) HCl (b) HI ✓ (c) HBr (d) HF
HI has the weakest H–I bond, hence decomposes easily.
Which oxide is the most basic oxide?
Options: (a) Na₂O ✓ (b) MgO (c) Al₂O₃ (d) SO₂
Sodium oxide reacts vigorously with water to form strong alkali NaOH.
Which group elements are the most reactive elements?
Options: (a) Group 17 (b) Group 1 ✓ (c) Group 18 (d) Group 2
Alkali metals lose electrons very easily making them highly reactive.
Which solution will turn dark because of a reaction?
Options: (a) Br₂ + NaCl (b) I₂ + NaBr (c) Cl₂ + NaCl (d) Cl₂ + NaI ✓
Chlorine displaces iodine forming dark violet solution.
X is a monoatomic gas. Which statement is correct?
Options: (a) X is reactive (b) X forms coloured compounds (c) X is unreactive ✓ (d) X forms ionic compounds
Noble gases are monoatomic and inert.
Which property is correct for group 1 elements?
Options: (a) Low catalytic activity ✓ (b) High catalytic activity (c) Coloured compounds (d) Strong oxidizing agents
2. Short Answer Questions
Explain why alkali metals become softer down the group.
As atomic size increases, metallic bonding weakens making the metals softer. Potassium can be cut like butter whereas lithium is hard.
Explain the reactivity of potassium with halogens.
Potassium reacts explosively with halogens forming potassium halides and emitting bright lilac flame.
Identify the reducing agent in Cl₂ + NaBr reaction.
Sodium bromide is reducing agent as Br⁻ loses electrons forming Br₂ while chlorine is reduced.
Explain why iodine is solid at room temperature.
Iodine has strong London dispersion forces between large molecules requiring high energy to separate them, keeping iodine solid.
State the role of Ni in hydrogenation.
Ni provides active surface for H₂ and oil to adsorb, breaking bonds and forming saturated compounds.
3. Constructed Response Questions
Which noble gas has the lowest boiling point and why?
Helium has weakest dispersion forces and thus lowest boiling point (−269°C), remaining gaseous at extremely low temperatures.
Describe the reactions of alkali metals with chlorine.
All alkali metals form crystalline chlorides. Li reacts slowly, Na vigorously (yellow flame), K explosively (lilac flame).
Explain why metals are solids at room temperature.
Strong metallic bonding holds atoms in close-packed lattice giving them high melting points and solid state.
Give examples of liquid elements.
Bromine (red-brown), Mercury (metallic), Gallium (melts on palm).
Explain why transition elements are unique.
They have variable oxidation states, form coloured complexes, and are used as catalysts (Ni, Fe, V₂O₅).
Compare chlorine and bromine as oxidizing agents.
Chlorine is more powerful and displaces Br₂ from bromides whereas bromine cannot displace chlorine.
Explain reactivity trend of halogens.
Reactivity decreases down the group due to increased atomic radius and weaker nuclear pull.
4. Descriptive Questions
Explain the role of catalytic converter in an automobile.
A catalytic converter is fitted in car exhaust system to reduce air pollution. It has a honeycomb structure coated with Pt, Pd, Rh. Hot exhaust gases pass over the catalyst where:
- CO → CO₂ (less poisonous)
- Unburnt hydrocarbons → CO₂ + H₂O
- NOₓ → N₂
This reduces smog and harmful emissions.
Explain why reactivities of alkali metals increase but those of halogens decrease down their groups.
In alkali metals, atomic size increases so outer electron is easily lost increasing reactivity. In halogens, atomic size increases reducing ability to gain electron, hence reactivity decreases.
Why are metals generally tough and strong whereas non-metals are not?
Metals have strong metallic bonding and delocalized electrons making them malleable and ductile. Non-metals are brittle as their covalent bonds break under stress.
Explain opposite roles of alkali metals and halogens.
Alkali metals are strong reducing agents (electron donors) while halogens are strong oxidizing agents (electron acceptors). They complement each other in redox reactions.
Why hydrogen bromide is thermally less stable than hydrogen chloride?
H–Br bond is longer and weaker than H–Cl, hence HBr breaks easily on heating making it less thermally stable.
Compare properties of metals and non-metals.
| Property | Metals | Non-Metals |
|---|
| State | Solid except Hg | Solid, liquid, gas |
| Lustre | Shiny metallic | Dull except Iodine |
| Malleability | Yes | No |
| Ductility | Yes | No |
| Conduction | Good conductors | Poor except graphite |
| Sonority | Sonorous | Not sonorous |
Give reasons why V₂O₅ is preferred over Pt as catalyst in Contact Process.
V₂O₅ is cheaper, resists poisoning by impurities, and gives high yield of SO₃ efficiently making it more practical than expensive platinum catalyst.
5. Investigative Questions
Explain the role of sodium as heat transfer agent in nuclear reactors.
Liquid sodium transfers heat quickly due to high thermal conductivity and remains stable at high temperature due to high boiling point.
Why does lithium behave differently from other alkali metals?
Lithium shows diagonal relationship with magnesium, is harder, less reactive, has higher melting point and forms covalent compounds that decompose on heating.
Why is aluminium preferred over magnesium for utensils?
Aluminium forms protective oxide coating, resists corrosion and conducts heat uniformly while magnesium is too reactive and flammable.