Periodic Classification of Elements – Very Short Answer Type Questions
CBSE • NCERT • Class 10
Chemistry — Chapter 14: Periodic Classification of Elements — 50 Very Short Answer Questions
Topic-wise very short questions with crisp answers — strictly aligned with NCERT for quick revision and board exam practice.
Practice order:
Basics → Periodic table structure → Trends → Groups & examples → Valency & formulas → Quick application questions
Basics → Periodic table structure → Trends → Groups & examples → Valency & formulas → Quick application questions
1. What does the modern periodic law state?
Properties of elements are periodic functions of their atomic numbers.
2. Who proposed the modern periodic law?
It is based on Mendeleev’s work but modern law uses atomic number (Z); concept refined by Moseley linking atomic number to proton count.
3. What is an element's atomic number?
The number of protons in the nucleus of an atom (equal to electrons in neutral atom).
4. Define a period in periodic table.
A horizontal row of elements; elements in a period fill the same principal energy level.
5. Define a group (family).
A vertical column; elements in a group have same number of valence electrons and similar chemical properties.
6. Give one example of Group 1 element.
Sodium (Na) — an alkali metal.
7. What is special about noble gases?
They have full valence shells and are chemically inert under normal conditions.
8. State one property trend across a period for atomic radius.
Atomic radius generally decreases from left to right across a period.
9. State one property trend down a group for atomic radius.
Atomic radius increases down a group.
10. How does ionization energy vary across a period?
Ionization energy generally increases from left to right across a period.
11. How does ionization energy vary down a group?
Ionization energy generally decreases down a group.
12. What is electronegativity (qualitative)?
A measure of an atom's tendency to attract shared electrons in a chemical bond.
13. Trend of electronegativity across a period?
Electronegativity generally increases across a period.
14. Trend of electronegativity down a group?
Electronegativity generally decreases down a group.
15. Where is hydrogen placed in periodic table?
Placed at top of Group 1 but is unique — can behave like alkali metal or halogen depending on context.
16. What is valency?
The combining capacity of an atom, often equal to number of electrons lost, gained or shared to attain stable configuration.
17. Valency of elements in Group 1?
1 (they commonly form +1 ions).
18. Valency of elements in Group 2?
2 (they commonly form +2 ions).
19. Valency of halogens (Group 17)?
1 (they commonly form −1 ions).
20. What is the electronic configuration notation for Group 18 noble gases (except He)?
ns² np⁶ (full outer shell).
21. Give an example of an element in Period 2.
Carbon (C), Nitrogen (N), Oxygen (O), etc.
22. Why does metallic character decrease across a period?
Because atoms more strongly attract electrons (higher ionization energy) and are less likely to lose electrons, reducing metallic behaviour.
23. Why does metallic character increase down a group?
Because valence electrons are farther from nucleus and more easily lost due to increased shielding.
24. What is the relation between atomic number and element identity?
Atomic number (Z) uniquely identifies an element — equal to proton count.
25. Mention one application of periodic trends.
Selecting materials: e.g., metals for conductors (low ionization energy), halogens for disinfectants (high reactivity).
26. What is an isotope (brief)?
Atoms of same element (same Z) with different mass numbers (different neutron counts).
27. Which group contains the most reactive non-metals?
Group 17 — the halogens (fluorine is the most reactive).
28. Which group contains highly reactive metals that react vigorously with water?
Group 1 — Alkali metals (react increasingly vigorously down the group).
29. State one property of alkali metals.
They are soft, react with water to form hydroxides and hydrogen, and have low ionization energies.
30. State one property of noble gases.
Inertness — very low chemical reactivity due to full valence shell.
31. How do you predict formula of compound between Group 1 and Group 17 element?
Combine charges: Group1(+1) and Group17(−1) → formula XY (e.g., NaCl).
32. Give formula for magnesium oxide.
MgO (Mg²⁺ with O²⁻ — charges balance 1:1).
33. How many valence electrons does oxygen have?
Six valence electrons (electronic configuration 2,6).
34. What is the common oxidation state of chlorine in sodium chloride?
−1 (Cl⁻).
35. Why is helium placed in Group 18 though its valence is 1?
Helium has full shell (1s²) like noble gases — chemical inertness places it with Group 18 despite ns configuration.
36. Why are transition metals not a focus in Class 10?
They involve d-orbitals, variable oxidation states, and advanced concepts usually covered in higher classes.
37. What is effective nuclear charge (simple)?
The net positive charge experienced by valence electrons after shielding by inner electrons.
38. How does effective nuclear charge change across a period?
It increases across a period, drawing valence electrons closer and reducing atomic radius.
39. Which element has higher ionization energy: Na or Mg?
Mg — because it has higher effective nuclear charge and holds electrons more tightly.
40. What are 'groups' used for in chemical predictions?
To predict chemical reactivity, valency and typical compounds of elements sharing group — useful for writing formulas.
41. How does electronegativity of fluorine compare to other elements?
Fluorine is the most electronegative element.
42. Give one use of noble gases.
Neon in advertising signs; argon as inert shield gas in welding.
43. What simple test shows similarities of group elements?
Compare reactions with water or oxygen—elements in same group show similar reaction patterns (e.g., Group1 with water).
44. How many elements are there in a period 3?
Eight elements (Na to Ar) in Period 3 for basic periodic table.
45. Name two elements used in household salts and their group numbers.
Sodium (Na, Group 1) and Chlorine (Cl, Group 17) — form NaCl.
46. What is the valency of aluminium and why?
3 — aluminium is in Group 13 with three valence electrons, tends to lose three to form Al³⁺.
47. Why does ionization energy of potassium (K) lower than sodium (Na)?
Because K's valence electron is in a higher shell further from nucleus and more shielded, making it easier to remove.
48. How does periodic table help predict chemical formula of compound?
By using valencies from group positions to balance charges and write empirical formulas (cross-over method).
49. Give one industrial application of halogens.
Chlorine used in water purification and sanitation.
50. What is the most important revision tip for this chapter?
Memorise group characteristics and trends, practise writing valencies and simple formulas, and use a one-page annotated periodic table for quick recall.