Question

Write the difference between isotopic, isobaric and isotonic nuclei. Give an example of each.

Hint:

Ask which quantity is equal: same atomic number Z means isotopes, same mass number A means isobars, same neutron number N = A - Z means isotones.

Answer 1

A nucleus is written as \( {}^{A}_{Z}X \), where \( Z \) = atomic number (number of protons), \( A \) = mass number (protons + neutrons) and the number of neutrons \( N = A - Z \).

Step 1: Isotopes (isotopic nuclei).
Nuclei having the same atomic number \( Z \) but different mass number \( A \) are called isotopes. They belong to the same element and have the same chemical properties but different numbers of neutrons.
Example: \( {}^{1}_{1}H,\ {}^{2}_{1}H,\ {}^{3}_{1}H \) (all have \( Z = 1 \)). Another: \( {}^{35}_{17}Cl \) and \( {}^{37}_{17}Cl \).

Step 2: Isobars (isobaric nuclei).
Nuclei having the same mass number \( A \) but different atomic number \( Z \) are called isobars. They are different elements with different chemical properties.
Example: \( {}^{40}_{18}Ar \) and \( {}^{40}_{20}Ca \) (both have \( A = 40 \)). Another: \( {}^{3}_{1}H \) and \( {}^{3}_{2}He \).

Step 3: Isotones (isotonic nuclei).
Nuclei having the same number of neutrons \( N = A - Z \) but different \( Z \) and different \( A \) are called isotones.
Example: \( {}^{30}_{14}Si \) and \( {}^{31}_{15}P \) (both have \( N = 16 \)). Another: \( {}^{13}_{6}C \) and \( {}^{14}_{7}N \) (both have \( N = 7 \)).

Summary.
\[\boxed{\text{Isotopes: same } Z\ \mid\ \text{Isobars: same } A\ \mid\ \text{Isotones: same } N}\]