Question

Isotopes are atom having the (a) same atomic number but different atomic masses (b) different atomic numbers but same atomic mass (c) same atomic number and atomic mass (d) different atomic numbers and atomic masses

Short answer

The correct option is (a) 'Same atomic number but different atomic masses' as it matches the definition of isotopes.

Step-by-step solution

Understanding isotopes

Isotopes are variants of a particular chemical element which differ in neutron number, and are thus differentiated by their atomic masses. They share the same atomic number (which means they belong to the same element) but have different atomic masses due to different numbers of neutrons.

Evaluating the options

Now, let's evaluate the options given. (a) 'Same atomic number but different atomic masses' matches our definition of isotopes. (b) 'Different atomic numbers but same atomic mass', this doesn't match our definition as isotopes belong to the same element and hence must have the same atomic number. (c) 'Same atomic number and atomic mass' implies that these are not isotopes, since isotopes of the same element have different atomic masses. (d) 'Different atomic numbers and atomic masses' definitely doesn't match our definition for isotopes, as they should belong to the same element and hence should have the same atomic number.

Key concepts

Atomic Number

The atomic number is a fundamental property of an element that reveals the number of protons in the nucleus of an atom. This number is represented by the symbol 'Z'. Elements are defined by their atomic number; for example, hydrogen has an atomic number of 1 because each hydrogen atom has one proton in its nucleus.

The significance of the atomic number comes into play when discussing isotopes, as it remains consistent across all isotopes of a given element. Despite the presence of different isotopes, which may vary in mass, the atomic number or the number of protons is a constant, identifying them as atoms of the same element. This uniformity is the reason why all isotopes of carbon, for example, are recognized as carbon.

Atomic Mass

Atomic mass is defined as the mass of an atom, which is primarily determined by the sum of protons and neutrons in its nucleus. This mass is often expressed in atomic mass units (u), with one atomic mass unit roughly equivalent to the mass of a single proton or neutron.

In the context of isotopes, while the atomic number remains constant, it is the variance in the number of neutrons that leads to different atomic masses. This is crucial to understand because two isotopes of the same element, with the same atomic number (Z), can have significantly different atomic masses. These mass differences can affect physical properties and behaviors, such as rates of diffusion or mass spectrometry readings.

Neutron Number

Neutrons, along with protons, make up the nucleus of an atom. While protons determine the atomic number, it is the neutrons that are variable in isotopes, thereby contributing to the different atomic masses without affecting the atomic number.

The neutron number, represented by the symbol 'N', provides an insight into the isotope of an element. For instance, carbon-12 and carbon-14 are isotopes of carbon sharing the same atomic number of 6 but differ in neutron number, holding 6 and 8 neutrons respectively. Therefore, when we encounter two isotopes of the same element, it is the neutron number that we consider to distinguish between them.