A sample of the first-ionization energies of eight consecutive main-group elements…
CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
A sample of the first-ionization energies of eight consecutive main-group elements (not given in order of atomic number) is provided in the table below.
Element | IE1 (kJmol−1)
A | 496
B | 419
C | 1000
D | 941
E | 1681
F | 1521
G | 738
H | 577
Additional information:
• Exactly one element in the set is a noble gas, and exactly one is an alkali metal.
• The elements are consecutive in atomic number.
Use the data to identify the elements and interpret periodic trends.
(a) Rank the eight elements from lowest to highest atomic number. Clearly state which entry in the table you identify as the alkali metal and which as the noble gas, providing justification based on quantitative or qualitative reasoning.
(b) Assign a chemical symbol to each letter (A–H). If multiple assignments appear plausible, state the evidence that eliminates the alternatives.
(c) Estimate the first-ionization energy that would directly precede element A in the periodic sequence. State any assumptions made and support your estimate with reference to the trend you established.
(d) Using Coulombic arguments and shielding considerations, explain why the difference between the IE1 of the alkali metal and the noble gas in this sequence is significantly larger than the differences between adjacent elements elsewhere in the table.