Which of these elements has the highest first ionisation energy?
A) Sodium (Z = 11)
B) Lithium (Z = 3)
C) Potassium (Z = 19)
D) Argon (Z = 18)
E) Neon (Z = 10)
IMAT 2023 · Question 43
Q43 - Periodic properties
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The correct answer is E) Neon (Z = 10).
Ionisation energy rises across a period and falls down a group, so the highest values belong to the noble gases at the top. Between neon and argon, neon is smaller and holds its electrons more tightly.
Roughly: Ne 2081, Ar 1521, Li 520, Na 496, K 419 kJ/mol.
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