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Difficulty: HardAtomic Structure and Periodic Table

A divalent metal cation (M2+M^{2+}) contains 1818 electrons. In the nucleus of this isotope, the number of neutrons is 44 greater than the number of protons. What is the mass number of this isotope?

Answer: 44

Answer

The mass number of this isotope is 4444.
A neutral atom that forms a divalent cation (M2+M^{2+}) loses 22 electrons. Since the cation has 1818 electrons, the neutral atom has 2020 electrons and therefore 2020 protons. The isotope has 44 more neutrons than protons, giving 20+4=2420 + 4 = 24 neutrons. The mass number is the sum of protons and neutrons: 20+24=4420 + 24 = 44.

Step-by-Step Solution

1
Determine the atomic number (number of protons) from the cation's charge and electron configuration.
Protons = 2020
A divalent cation (M2+M^{2+}) has lost 22 electrons relative to its neutral state. The neutral atom therefore has 18+2=2018 + 2 = 20 electrons and, correspondingly, 2020 protons.
2
Calculate the total number of neutrons in the nucleus.
Neutrons = 2424
The problem specifies that the number of neutrons exceeds the number of protons by 44, giving 20+4=2420 + 4 = 24 neutrons.
3
Sum the protons and neutrons to obtain the mass number (AA).
Mass number = 4444
The mass number of an isotope is defined as the total number of nucleons (protons plus neutrons): 20+24=4420 + 24 = 44.

Key Concept

Calculation of atomic number and mass number from ionic charge and subatomic particle relationships.
Estimated Time:1m 30s
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Topics

Atomic Structure and Periodic Table

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