Isotones-Definition, Examples, Practice Problems, Frequently Asked Questions

When, somebody confronts you with a question of milestones in the history of atom, definitely you will start naming and narrating them, starting from the discovery of electrons. The discovery of the electron i.e the negative charge in the atom. This discovery is generally credited to Nobel prize winning scientist JJ Thompson.

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Then the discovery of the nucleus, or the positive centre of the atom. Then came the proton, which was found to be the positively charged subatomic particle. However, one of the most important milestones is the discovery of neutron. This is because the neutron has no charge or is neutral in nature. All the above discoveries of electron or proton is easier because they were predominantly based on the deflection or repulsion of particles that stems from the idea that “likes repels and opposites attract”. But neutrons did not repel or get repelled by the positive and negative flow charges by virtue of being neutral in nature. However, neutrons contribute to a significant part of the mass of the atom. But also, it has an important function. It acts as a binding agent, to be very crass, in the nucleus. It holds together the protons so that their repulsions do not push the parts of the nucleus away.

As we move to higher atomic numbers, the number of neutrons required to hold together a stable nucleus generally increases. Neutrons themselves play a vital role in nuclear chemistry. There’s a fun application of neutrons which goes by the name “isotones”. Sounds like a lot of names we already know-isomers, isotopes…Let us try and understand this concept in more detail today.

TABLE OF CONTENTS:

Definition
Interesting examples
Practice Problems
Frequently asked questions

DEFINITION

Isotones are nuclei that have different atomic numbers (number of protons) but same neutron number (number of neutrons). In other words, we can say that they have the same A-Z value. For instance, H-2 and He-3 are a pair of isotones with one neutron each in their nucleus. German physicist K. Guggenheimer coined the term "isotones." He created the phrase by replacing the proton-designating “p” in isotope with the neutron-designating “n”.

INTERESTING EXAMPLES

B - 12 and C - 13 are isotones.
Kr - 86, Y - 89, Zr - 90, Mo - 92 and Ra - 88 are all isotones with fifty neutrons.
S - 36, Cl - 37, Ar - 38, K - 39 and Ca - 40 are isotones of neutron value twenty.
H - 2 and He - 3 are the only pair of isotones having one neutron..

PRACTICE PROBLEMS

Q1. Give an example of an isotone for C - 14.

Answer: C - 14 has A = 14 and Z = 6. So number of neutrons = A-Z = 14 - 6 = 8. So now any species which has 8 neutrons will be an isotone of C - 14. An example of such a species is O - 16. Hence, C - 14 and O - 16 are neutron eight isotopes.

Q2. How are As - 77 and Se - 78 related?

Ans: As-77 has A-Z value = 77-33 = 44. Hence, As-77 has a neutron value of 44. Se-78 has A-Z value = 78-34 = 44. Se-78 also has a neutron value of 44. Hence, both the species have a neutron value of 44, thereby making them isotones.

Q3. Can Ca-39 and Ca-40 be isotones?

Ans: In the case of Ca-39, A = 39, Z = 20, A-Z = 19. For Ca-40 A = 40, Z = 20, A-Z = 20. As we can see, here the A-Z value is not the same for both these species. So they cannot be isotones. However, as is visible, they have the same Z value which means they are isotopes.

Q4. In isotones which of the following is same?

A). Number of protons
B). Number of Neutrons
C) Both number of both neutrons and protons
D). Number of electrons.

Answer Correct option is B. In isotones number of neutrons will be same. Number of electrons and protons can vary.

FREQUENTLY ASKED QUESTIONS

Q1. How are isotones and isodiaphers different?

Answer: Isotones are a set of species which have the same number of neutrons i.e. the same value of A-Z. But isodiaphers are a set of species which have the same value of neutron excess i.e. the same value of A-2Z.

Q2. What are isosteres?

Answer: Any species, be it an atom, ion or radical, if they have the same number of valence electrons, and are roughly of the same size, they are called isosteres. For instance, O^2- and F^- are isosteres. This is not the same as isoelectronic species.

Q3. Differentiate isotopes and isotones.

ans. Isotope have same number of protons and different number of neutrons.Isotones on the other hand have same number of neutrons with different number of protons.