An element has an atomic number of 8 and a mass number of 16. How many neutrons does this element have?

Analysis

To find the number of neutrons in an atom, we need to understand the relationship between the atomic number, the mass number, and the subatomic particles (protons, neutrons, and electrons).

Concept

• Atomic Number ($Z$): This represents the number of protons in the nucleus of an atom. For a neutral atom, it is also equal to the number of electrons.
• Mass Number ($A$): This is the sum of the number of protons and the number of neutrons in the nucleus.
• Formula: $$\text{Mass Number} (A) = \text{Number of Protons} (Z) + \text{Number of Neutrons} (n)$$Therefore, to find the number of neutrons:$$\text{Neutrons} (n) = \text{Mass Number} (A) - \text{Atomic Number} (Z)$$

Step-by-Step Solution

1. Identify the given values: • Atomic Number ($Z$) = 8 • Mass Number ($A$) = 16
2. Apply the formula: • $n = A - Z$ • $n = 16 - 8$
3. Calculate the result: • $n = 8$

The element described is Oxygen, which has 8 protons and 8 neutrons.

Conclusion

The number of neutrons is 8. Comparing this to your options: A. 24 B. 16 C. 8 D. 32

The correct option is C.

Exam Tip

Always remember the acronym MAN: Mass number = Atomic number + Neutrons. If you are ever asked for neutrons, just subtract the smaller number (atomic number) from the larger number (mass number).