Q4. Using ν ≈ 2.47 × 10 (Z − 1) Hz, find the ratio of the Kα X-ray frequencies of copper (Z = 29) and iron (Z = 26).
Ratio = (29 − 1) ÷ (26 − 1) = 784 ÷ 625 = 1.25. Copper’s X-rays have about 1.25 times the frequency of iron’s.
Q5. An element’s Kα X-rays have a frequency of 1.94 × 10 Hz. Use Moseley’s relation to find its atomic number.
(Z − 1) = (1.94 × 10) ÷ (2.47 × 10) = 785, so Z − 1 = 28.0 and Z = 29: copper.
Q6. Why do isotopes of an element not need separate places in the modern periodic table?
Isotopes have the same atomic number (the same number of protons and electrons), so they have the same electronic configuration and very similar chemistry (small isotope effects are possible). The modern table is ordered by atomic number, so they share one place.
Q7. Which period and group does the element with Z = 20 belong to?
After argon (18), period 4 begins: Z = 19 is in group 1 and Z = 20 in group 2. It is calcium, period 4, group 2.
Q8. In terms of period and group, where would you place the element with Z = 114 (NCERT Exercise 3.5, page 96)?
Period 7 runs from Z = 87 to 118, and 118 is in group 18, so 114 is four places earlier: period 7, group 14, below lead. It is flerovium (Fl).