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Difficulty: HardAtomic Structure and Periodic Table

An isotope of an element has a mass number of 7979 and contains 4545 neutrons in its nucleus. If this neutral atom gains the minimum number of electrons required to achieve a stable octet in its outermost valence shell, what is the total number of subatomic particles (protons, neutrons, and electrons combined) in the resulting ion?

  1. A
    111111
  2. B
    113113
  3. 115115Answer
  4. D
    126126

Answer

115 total subatomic particles
The atomic number is determined by subtracting the number of neutrons from the mass number: 79−45=3479 - 45 = 34 protons. An element with 3434 protons has 66 valence electrons in its outer shell (configuration 2,8,18,62, 8, 18, 6) and requires 22 additional electrons to form a stable octet, resulting in 3636 electrons. The sum of all subatomic particles in the ion is 34 protons+45 neutrons+36 electrons=11534\text{ protons} + 45\text{ neutrons} + 36\text{ electrons} = 115.

Step-by-Step Solution

1
Calculate the atomic number (number of protons) of the neutral atom
Protons = 79−45=3479 - 45 = 34
The mass number (AA) equals the sum of protons (ZZ) and neutrons (NN), so Z=A−NZ = A - N.
2
Determine the number of valence electrons and electrons needed to achieve a stable octet
Valence electrons = 66; electrons to gain = 8−6=28 - 6 = 2
An element with atomic number 3434 has an electron configuration of 2,8,18,62, 8, 18, 6. It requires 22 additional electrons to fill its outer shell with 88 valence electrons.
3
Determine the total number of electrons in the resulting ion
Electrons = 34+2=3634 + 2 = 36
Gaining 22 electrons to form a stable 2−2- anion increases the electron count from 3434 to 3636.
4
Sum all subatomic particles (protons, neutrons, and electrons)
Total particles = 34+45+36=11534 + 45 + 36 = 115
The total particle count is the sum of protons (3434), neutrons (4545), and electrons (3636).

Key Concept

Calculating subatomic particle totals using mass number, neutron count, valence electron configurations, and ion formation.
Estimated Time:1m 30s
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Topics

Atomic Structure and Periodic Table

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