A neutral atom has 2 electrons in its first energy level, 8 electrons in its second energy… — Armed Services Vocational Aptitude Battery (ASVAB)

A neutral atom has $2$ electrons in its first energy level, $8$ electrons in its second energy level, and $6$ valence electrons in its third energy level. If the mass number of this atom is $34$ , what is the total number of neutrons located in its nucleus?

A
$16$
B
$28$
$18$ Answer
D
$50$

Answer

18

neutrons

In a neutral atom, the total number of electrons equals the number of protons (atomic number,

Z

). Summing the electrons across all three energy levels (

2 + 8 + 6

) yields

16

electrons, which means the nucleus contains

16

protons. Because mass number (

A

) is the sum of protons and neutrons (

A = Z + N

), the number of neutrons is found by subtracting the protons from the mass number:

34 - 16 = 18

Step-by-Step Solution

Calculate the total number of electrons in the neutral atom by summing all energy levels.

2 + 8 + 6 = 16

electrons

The total electron count is the sum of electrons distributed across the inner shells and the valence shell.

Determine the atomic number (number of protons) from the electron count.

Atomic number (

Z

) =

16

protons

In any neutral atom, the number of positively charged protons equals the number of negatively charged electrons.

Calculate the number of neutrons by subtracting the atomic number from the mass number.

Number of neutrons =

34 - 16 = 18

Mass number (

A

) equals protons (

Z

) plus neutrons (

N

), so

N = A - Z

Key Concept

Subatomic particle relationships and electron configuration in neutral atoms

Estimated Time:1m 0s

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