The atoms of different elements containing the same number of neutrons, but different atomic number (or different number of protons and electrons) are called **isotones**. In simple words, isotones are atoms or nuclei of different elements that contains an identical number of neutrons, but different number of protons and electrons.

For example, ^{13}C_{6} (Carbon-13) and ^{14}N_{7} (Nitrogen-14) are isotones because they both contain the same number of neutrons (7), but they have different atomic numbers (6 for carbon and 7 for nitrogen) and different mass numbers (13 and 14, respectively).

The term isotones is derived from a combination of Greek words: “**isos**” meaning **equal**, and “**tonos**” meaning **tension** or **strain**. In nuclear chemistry, however, the word “isotones” refers to nuclei of different chemical elements that have the same number of neutrons but different numbers of protons and electrons.

## Table of Contents

## Key Characteristics of Isotones

There are the following important characteristics of isotones that you should keep in mind. They are as:

- Isotones have the same number of neutrons in the nuclei of different elements.
- They have different atomic numbers because the number of protons and electrons varies between elements.
- They have different mass numbers because the total number of protons and neutrons is different.
- Since they belong to different elements, isotones exhibit different chemical behaviors.

## How to Identify Isotones?

To identify isotones, we look at the number of neutrons in the nuclei of different elements. The neutron number (N) is calculated by subtracting the atomic number (Z) from the mass number (A) of an element:

**Number of neutrons (N)** = Atomic number (Z) − Mass number (A)

If two nuclei from distinct elements have the same value of N (number of neutrons), they are considered as isotones. Let’s take examples on it to understand better.

## Top Five Examples of Isotones

To further clarify the concept of isotones, let’s take some specific examples of isotones that have the same number of neutrons but differ in their number of protons.

Chlorine-37 (**Example 1:**^{37}Cl_{17}) and Potassium-39 (^{39}K_{19})

**Chlorine-37:**

- Atomic number (Z) = 17 (protons)
- Mass number (A) = 37
- Number of neutrons (N) = 37−17 = 20

**Potassium-39:**

- Atomic number (Z) = 19 (protons)
- Mass number (A) = 39
- Number of neutrons (N) = 39−19 = 20

Both Chlorine-37 and Potassium-39 have the same neutron number (N = 20), making them isotones.

Carbon-14 (**Example 2:**^{14}C) and Nitrogen-15 (^{15}N)

**Carbon-14:**

- Atomic number (Z) = 6 (protons)
- Mass number (A) = 14
- Neutron number (N) = 14 − 6 = 8

**Nitrogen-15:**

- Atomic number (Z) = 7
- Mass number (A) = 15
- Neutron number (N) = 15 − 7 = 8

Carbon-14 and Nitrogen-15 are also isotones because of having the same neutron number (N = 8).

**Example **3:^{14}C_{6}, ^{15}N_{7}, and ^{16}O_{8}

Isotones | Atomic number (Z) | Mass number (A) | Electrons (e) | Protons (p) | Neutrons (n) |
---|---|---|---|---|---|

^{14}C_{6} | 6 | 14 | 6 | 6 | 14 – 6 = 8 |

^{15}N_{7} | 7 | 15 | 7 | 7 | 15 – 7 = 8 |

^{16}O_{8} | 8 | 16 | 8 | 8 | 16 – 8 = 8 |

^{14}C_{6}, ^{15}N_{7}, and ^{16}O_{8} are isotones because each has the same number of neutrons.

Oxygen-18 (**Example **4:^{18}O) and Fluorine-19 (^{19}F)

**Oxygen-18:**

- Atomic number Z = 8
- Mass number A = 18
- Neutron number N = 18 − 8 = 10

**Fluorine-19:**

- Atomic number Z = 9
- Mass number A = 19
- Neutron number N = 19 − 9 = 10

Here, Oxygen-18 and Fluorine-19 have the same neutron number (N = 10), which makes them isotones.

Sodium-23 (**Example **5:^{23}Na_{11}) and Magnesium-24 (^{24}Mg_{12} )

**Sodium-23:**

- Atomic number Z = 11
- Mass number A = 23
- Neutron number N = 23 − 11 = 12

**Magnesium-24:**

- Atomic number Z = 12
- Mass number A = 24
- Neutron number N = 24 − 12 = 12

Sodium-23 and Magnesium-24 are isotones since both nuclei have the same number of neutrons (12).

## Difference between Isotopes, Isobars, and Isotones

Here is the difference between isotones, isotopes, and isobars in table form:

Property | Isotopes | Isobars | Isotones |
---|---|---|---|

Definition | Atoms with the same atomic number but different mass numbers. | Atoms with the same mass numbers but different atomic numbers. | Atoms of different elements with the same number of neutrons. |

Atomic number (Z) | Same | Different | Different |

Number of neutrons (N) | Different | Different | Same |

Mass number (A) | Different | Same | Different |

Element type | Same element | Different elements | Different elements |

Example | Carbon-12 (^{12}C_{6}) and Carbon-14 (^{14}C_{6}) | Carbon-14 (^{14}C_{6}) and Nitrogen-14 (^{14}N_{7}) | Sodium-23 (^{23}Na_{11}) and Magnesium-24 (^{24}Mg_{12}) |

## Numerical Examples and Calculations

Let’s take some important numerical examples to further illustrate the isotone concept.

Finding Isotones of Carbon-13**Example **6:

To find the isotones of Carbon-13 (13C), we need to look for elements with the same number of neutrons as Carbon-13, which has:

- Atomic number Z = 6 (protons)
- Mass number A = 13
- Neutron number N = 13 − 6 = 7

So, isotones of Carbon-13 will be elements with a neutron number of 7. Let’s calculate the number of neutrons for some elements:

**Nitrogen-14 ( ^{14}N):**

- Atomic number Z = 7 (protons)
- Mass number A = 14
- Neutron number N = 14 − 7 = 7

**Oxygen-15 ( ^{15}O):**

- Atomic number Z = 8 (protons)
- Mass number A = 15
- Neutron number N = 15 − 8 = 7

Thus, Nitrogen-14 and Oxygen-15 are isotones of Carbon-13.

Identifying Isotones in Higher Atomic Numbers**Example **7:

Let us consider Krypton-86 (^{86}Kr) and Strontium-88 (^{88}Sr)

**Krypton-86**:

- Atomic number Z = 36
- Mass number A = 86
- Neutron number N = 86 − 36 = 50

**Strontium-88**:

- Atomic number Z = 38
- Mass number A = 88
- Neutron number N = 88 − 38 = 50

Both Krypton-86 and Strontium-88 have the same neutron number (N = 50), making them isotones.

## Uses of Isotone

The following are a few real life uses of isotone in everyday life.

- Isotones are used in the production of technetium -99, which is commonly used for medical imaging in nuclear medicine, such as in diagnostic scans.
- They are also used in the production of easily fissionable materials, which are essential in nuclear reactors for power generation and nuclear research.
- Some isotones are used to create fissionable materials used in the development of nuclear weapons.
- Isotone acts as a neutron absorber in nuclear reactors, which helps to control the chain reactions during nuclear fission and maintain the safe operation of reactors.