Questions: 10. What is an isotope? 11. What subatomic particles make up an atom? 12. Which subatomic particles make up atomic mass? 13. What is the average atomic mass of element X if, X - 123 has a relative abundance of 12%, X 127 has a relative abundance of 18%, and X-125 has a relative abundance of 70%?

Solution Steps

An isotope is a variant of a particular chemical element which differs in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom.

\(\boxed{\text{An isotope is a variant of an element with the same number of protons but different numbers of neutrons.}}\)

An atom is made up of three types of subatomic particles:

1. Protons (positively charged)
2. Neutrons (neutral)
3. Electrons (negatively charged)

\(\boxed{\text{Protons, Neutrons, and Electrons}}\)

The atomic mass of an atom is primarily determined by the sum of the masses of protons and neutrons, as electrons have negligible mass.

\(\boxed{\text{Protons and Neutrons}}\)

To find the average atomic mass of element \(X\), we use the relative abundances and masses of its isotopes. The formula is:

\[ \text{Average Atomic Mass} = \sum (\text{isotope mass} \times \text{relative abundance}) \]

Given:

• \(X-123\) with a relative abundance of \(12\%\)
• \(X-127\) with a relative abundance of \(18\%\)
• \(X-125\) with a relative abundance of \(70\%\)

Convert percentages to decimals:

• \(12\% = 0.12\)
• \(18\% = 0.18\)
• \(70\% = 0.70\)

Calculate the average atomic mass: \[ \text{Average Atomic Mass} = (123 \times 0.12) + (127 \times 0.18) + (125 \times 0.70) \]

\[ = 14.76 + 22.86 + 87.50 \]

\[ = 125.12 \]

\(\boxed{125.1}\)

Final Answer