The isotopes of neon are represented by the symbols $^{20}$$_{x}$ Ne, $^{21}$ $_{y}$ Ne, and $^{22}$ $_{z}$ Ne. The relationship between x, y, and z is?

Analyze the question The symbols ²⁰ₓNe, ²¹ᵧNe and ²²_zNe are written with the mass number on top and the atomic number (x, y, z) at the bottom. The question asks how x, y and z are related.

Concept

• Isotopes are atoms of the same element with the same atomic number (the same number of protons) but different mass numbers (different numbers of neutrons).
• The atomic number identifies the element. All of these atoms are neon, so they must have the same atomic number.

Solution

1. All three atoms are neon (Ne), so each has atomic number 10.
2. Therefore x = y = z = 10.
3. What differs is the number of neutrons: • ²⁰Ne has 20 − 10 = 10 neutrons • ²¹Ne has 21 − 10 = 11 neutrons • ²²Ne has 22 − 10 = 12 neutrons

The mass numbers (20, 21, 22) are different, but the atomic numbers x, y and z are equal.

Answer: C (x = y = z).

Tip For isotopes, remember that the atomic number (Z) stays the same and only the mass number (A) changes. Whenever a question asks you to compare the atomic numbers of isotopes, the answer is "equal".