Chemistry, 15.10.2019 22:40 MogTaee

Which two notations represent isotopes of the same element

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The two notations that represent isotopes of the same element is $\boxed{_{\text{7}}^{{\text{14}}}{\text{N and }}_{\text{7}}^{{\text{18}}}{\text{N}}}$

Further explanation:

An atom is also written as $_{\text{Z}}^{\text{A}}{\text{X}}$ , where A is the mass number, Z is the atomic number, and X is the letter symbol of the element.

Isotopes:

Atoms of the same element with same atomic number but different mass numbers are called isotopes. Isotopes have the equal number of protons but the number of neutrons is different.

$_{\mathbf{6}}^{{\mathbf{11}}}{\mathbf{C}}$ and $_{\mathbf{6}}^{{\mathbf{12}}}{\mathbf{C}}$ are examples of isotopes. Both are the atoms of the same element carbon. The mass number of $_6^{11}{\text{C}}$ is 11 while that of $_6^{12}{\text{C}}$ is 12. But both of these have the same atomic number and that is 6.

(1) $_{\mathbf{7}}^{{\mathbf{14}}}{\mathbf{ N and }}_{\mathbf{7}}^{{\mathbf{18}}}{\mathbf{N}}$

Here, both elements are the same (nitrogen). The atomic numbers of both nitrogens are same. But the atomic mass or mass number of $_7^{14}{\text{N}}$ is 14 while that of $_7^{18}{\text{N}}$ is 18. So both the notations have the same atomic number and different mass numbers. So this pair completely satisfies the definition of isotopes and therefore it is a correct option.

(2) $_{\mathbf{7}}^{{\mathbf{14}}}{\mathbf{ Nand }}_{{\mathbf{10}}}^{{\mathbf{17}}}{\mathbf{Ne}}$

Here, both elements are not the same. One element is nitrogen while the other one is neon. The atomic numbers of both elements are different. The atomic number of nitrogen atom is 7 while that of neon is 10. The atomic masses of both elements are also different. So this pair does not satisfy the definition of isotopes and therefore, it is an incorrect option.

(3) $_{\mathbf{7}}^{{\mathbf{20}}}{\mathbf{N and }}_{{\mathbf{10}}}^{{\mathbf{20}}}{\mathbf{Ne}}$

Here, both elements are not the same. One element is nitrogen while the other one is neon. The atomic numbers of both elements are different. The atomic number of nitrogen atom is 7 while that of neon is 10. The atomic masses of both elements are same. So this pair does not satisfy the definition of isotopes and therefore it is an incorrect option.

(4) $_{\mathbf{7}}^{{\mathbf{19}}}{\mathbf{N and }}_{{\mathbf{10}}}^{{\mathbf{16}}}{\mathbf{Ne}}$

Learn more:

1. Forces in ionic compounds: link

2. Reason for the acidic and basic nature of amino acid: link

Answer details:

Grade: High School

Subject: Chemistry

Chapter: Atomic structure

Keywords: isotopes, same element, notations, represent, same atomic number, different mass numbers, A, Z, X, nitrogen, neon, 7, 10, correct, incorrect.

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