Periodic Table — First Look

Q1. (3 marks)

• Modern Periodic Law: "The physical and chemical properties of elements are a periodic function of their atomic numbers." (2)
• The table is based on atomic number (Z). (1)

Q2. (4 marks) (a) Achievement (any one): Left gaps for undiscovered elements and predicted their properties (e.g. eka-silicon = germanium); or grouped elements with similar properties together. (2) (b) Drawback (any one): No fixed place for isotopes; position of hydrogen uncertain; some pairs placed in wrong order of mass (e.g. Ar before K). (2)

Q3. (4 marks — 1 each) (a) 18 groups, 7 periods. (b) d-block. (c) Group 1 (alkali metals).

Q4. (5 marks — 1 each) Sodium = Na; Potassium = K; Iron = Fe; Copper = Cu; Silver = Ag.

Q5. (4 marks — 1 each) Silicon = metalloid; Sulfur = non-metal; Magnesium = metal; Boron = metalloid.

Q6. (4 marks — 2 per correct contrasting property)

Any two valid contrasting rows. (2 + 2)

Q7. (4 marks — 1 each) (a) Na: $1s^2\,2s^2\,2p^6\,3s^1$ → last electron in s → s-block. (b) Cl: $\ldots 3s^2\,3p^5$ → last electron in p → p-block. (c) He: $1s^2$ → s-block (although in Group 18 due to full shell). (d) Sc: $\ldots 3d^1\,4s^2$ → last electron in d → d-block.

Q8. (4 marks) (a) $1s^2\,2s^2\,2p^6\,3s^2$ (or 2, 8, 2). (2) (b) Group 2, Period 3. (1) — valence electrons = 2 → Group 2; highest shell n = 3 → Period 3. (c) Metal (it is Magnesium). (1)

Q9. (4 marks — 2 each) (a) Metalloid: an element that shows properties intermediate between metals and non-metals (e.g. B, Si, Ge, As). (2) (b) Period: a horizontal row in the periodic table; elements in a period have the same number of occupied electron shells (same highest principal quantum number n). (2)

Q10. (4 marks)

• By atomic mass, Ar (39.9) > K (39.1), so Ar would come after K — but Ar is a noble gas and K a reactive metal, giving them wrong groups. (2)
• By atomic number, Ar (Z = 18) correctly comes before K (Z = 19), placing each in its proper group. Hence atomic number, being the fundamental property, removes such anomalies. (2)

[
  {"claim":"Element Z=12 (Mg) has valence electrons=2, giving Group 2, Period 3",
   "code":"n=12; shells=[2,8,2] if n==12 else []; valence=shells[-1]; period=len(shells); group=valence; result=(valence==2 and period==3 and group==2)"},
  {"claim":"Na Z=11 last electron fills 3s (s-block)",
   "code":"config=[('1s',2),('2s',2),('2p',6),('3s',1)]; total=sum(e for _,e in config); last=config[-1][0]; result=(total==11 and last=='3s')"},
  {"claim":"Argon (mass 39.9) is heavier than Potassium (mass 39.1) despite lower atomic number",
   "code":"Ar_mass=39.9; K_mass=39.1; Ar_Z=18; K_Z=19; result=(Ar_mass>K_mass and Ar_Z<K_Z)"},
  {"claim":"Modern table has 18 groups and 7 periods",
   "code":"groups=18; periods=7; result=(groups==18 and periods==7)"}
]