MHT-CET Chemistry · Free notes
Elements of Group 16, 17 and 18 — MHT-CET Chemistry
Groups 16, 17 and 18 is about one question a paper in MHT-CET Chemistry and almost never HARD — three of its 81 past-year questions. It is a chapter of trends and named facts: how size, ionisation enthalpy, hydride stability and acidity change down a group, the oxygen and sulphur compounds and ores, the halogen oxoacids and interhalogens, and the shapes of the xenon compounds. Three pages, one for each group. Every PYQ is tagged.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Group 16: Chalcogen Trends, Hydrides, Oxygen, Ozone and Sulphur
37 PYQsThe chalcogens O, S, Se, Te and Po (ns² np⁴) grow larger, denser, less reactive and easier to ionise down the group; their hydrides H₂E become less stable but more acidic; oxygen forms O₂ and the less stable, strongly oxidising O₃; and sulphur has the most allotropes and gives SO₂, sulphuric acid and oleum.
Group 17: Halogens, Their Oxoacids and Interhalogen Compounds
37 PYQsThe halogens F, Cl, Br, I and the radioactive At (ns² np⁵) change from gases to a liquid to a solid down the group, form less stable hydrogen halides as the atom grows, and give oxoacids HOX, HXO₂, HXO₃ and HXO₄ whose strength rises with the oxidation state; two different halogens combine as interhalogens XX′ₙ with n always odd.
Group 18: Noble Gases, Their Uses and the Shapes of Xenon Compounds
7 PYQsThe noble gases He, Ne, Ar, Kr, Xe and Rn have filled valence shells and few compounds, but xenon combines with fluorine and oxygen, and the shape of each xenon compound follows from its bond pairs and lone pairs exactly as for an interhalogen.
Formula & revision sheet
6 formulas · 2 reference tables · 8 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
6 formulas · 2 reference tables · 8 gotchas across all subtopics — the exam-eve cheat-sheet
Formulas (3)
Reference tables (1)
Sulphur: Allotropes, SO₂, Oleum and Ores6 rows
| Name | Formula | Remember |
|---|---|---|
| Oleum | H₂S₂O₇ | H₂SO₄ + SO₃ H₂S₂O₃ is thiosulphuric, H₂S₂O₈ peroxodisulphuric. |
| Galena | PbS | lead ore |
| Baryte | BaSO₄ | Ba, S, O |
| Zinc blende | ZnS | roasted for SO₂ |
| Iron pyrites | FeS₂ | roasted for SO₂ |
| Gypsum | CaSO₄·2H₂O | — |
Watch out for (4)
- Putting astatine in group 16→ The Chalcogen Family and Its Trends
- Expecting stability and acidity to run the same way→ Hydrides H₂E and Oxygen Against Sulphur
- Calling ozone paramagnetic like oxygen→ Dioxygen and Ozone
- Taking the S–S–S angle as 104.5° or 120°→ Sulphur: Allotropes, SO₂, Oleum and Ores
Formulas (2)
Reference tables (1)
Oxoacids of the Halogens4 rows
| Name | Formula | O.S. of Cl | Cl–O bonds |
|---|---|---|---|
| Hypochlorous | HOCl | +1 | 1 single |
| Chlorous | HClO₂ | +3 | 1 single, 1 double |
| Chloric | HClO₃ | +5 | 1 single, 2 double |
| Perchloric | HClO₄ | +7 | 1 single, 3 double The strongest oxoacid. |
Watch out for (3)
- Putting HI above HF in boiling point→ Halogen Properties and the Hydrogen Halides
- Reading 'halous' as the lowest acid→ Oxoacids of the Halogens
- Assuming the iodine interhalogens are all solids→ Interhalogen Compounds
Watch out for (1)
- Counting an Xe=O bond as one electron→ Noble Gas Uses and Xenon Compound Shapes
PYQ weightage by concept
8 concepts · 81 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
8 concepts · 81 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| The Chalcogen Family and Its Trends | 8 | 10% |
| Hydrides H₂E and Oxygen Against Sulphur | 6 | 7% |
| Sulphur: Allotropes, SO₂, Oleum and Ores | 6 | 7% |
| Dioxygen and Ozone | 4 | 5% |
| Concept | PYQs | Share |
|---|---|---|
| Interhalogen Compounds | 8 | 10% |
| Halogen Properties and the Hydrogen Halides | 7 | 9% |
| Oxoacids of the Halogens | 6 | 7% |
| Concept | PYQs | Share |
|---|---|---|
| Noble Gas Uses and Xenon Compound Shapes | 3 | 4% |
Test yourself on Elements of Group 16, 17 and 18
15 past MHT-CET questions from this chapter, timed at 14 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.