Question

Elemental iridium is composed of two stable isotopes, iridium-191 and iridium-193. (a) How many protons and neutrons are found in these two isotopes of iridium? (b) Write the correct isotopic notation for each of these isotopes of iridium. (c) Calculate the mass percent of protons in the nucleus of each of these isotopes.

Short answer

Iridium has 77 protons. Isotopes iridium-191 and iridium-193 have 114 and 116 neutrons respectively. Their correct isotopic notations are \(^{191}_{77}Ir\) and \(^{193}_{77}Ir\). The mass percent of protons in iridium-191 and iridium-193 are approximately 40.31% and 39.90% respectively.

Step-by-step solution

Determine the number of protons for iridium isotopes

The number of protons is determined by the atomic number of the element iridium, found on the periodic table. The atomic number of iridium is 77, which means each iridium isotope has 77 protons.

Calculate the number of neutrons in each isotope

The number of neutrons in an isotope is found by subtracting the atomic number from the mass number. For iridium-191, the number of neutrons is 191 - 77 = 114. For iridium-193, the number of neutrons is 193 - 77 = 116.

Write isotopic notation for each isotope

Isotopic notation includes the element's symbol (Ir), the mass number (A, the sum of protons and neutrons), and the atomic number (Z, the number of protons). For iridium-191, the notation is \(^{191}_{77}Ir\). For iridium-193, the notation is \(^{193}_{77}Ir\).

Calculate mass percent of protons in iridium-191

The mass percent of protons = (number of protons / mass number) * 100. For iridium-191, it is (77 / 191) * 100 = 40.3141%.

Calculate mass percent of protons in iridium-193

Similarly, for iridium-193, the mass percent of protons is (77 / 193) * 100 = 39.8964%.

Key concepts

Atomic Number

The atomic number of an element is one of the fundamental identifiers in chemistry. It represents the number of protons found in the nucleus of an atom and is unique to each element. For instance, iridium has an atomic number of 77, which means that each atom of iridium holds exactly 77 protons, regardless of its isotope.

This number not only determines the element's identity on the periodic table but also its chemical properties, as it defines the element's position in the periodic system. Knowing the atomic number is crucial when examining isotopes because it remains constant, distinguishing the isotopes by their differing numbers of neutrons.

Neutron Calculation

Counting neutrons is a simple yet essential task for understanding isotopes. For any isotope, the number of neutrons can be calculated by subtracting the atomic number, which is the count of protons, from the mass number of the isotope. The mass number is a sum of the protons and neutrons in the nucleus.

For example, in the iridium isotopes, iridium-191 and iridium-193, the calculations are direct:

• Iridium-191: 191 (mass number) - 77 (atomic number) = 114 (number of neutrons)
• Iridium-193: 193 (mass number) - 77 (atomic number) = 116 (number of neutrons)

These calculations are fundamental in understanding isotopic differences and nuclear chemistry.

Isotopic Notation

Isotopic notation provides a concise way to convey all the necessary information about an isotope's nucleus — its element, number of protons, and number of nucleons (protons plus neutrons). Usually, isotopic notation is depicted with the mass number as a superscript and the atomic number as a subscript on the left side of the chemical symbol.

Considering iridium-191 and iridium-193, the notations would be as follows:

• For iridium-191: \(^{191}_{77}Ir\)
• For iridium-193: \(^{193}_{77}Ir\)

In these notations, 'Ir' represents the element iridium, 77 is the atomic number indicating the number of protons, and 191 or 193 is the mass number showing the total number of protons and neutrons.

Mass Percent Calculation

The mass percent calculation is a way to express the proportion of a certain type of particle within an atom. Specifically, it can be used to determine the percentage of the atom's mass that is due to protons. To find the mass percent of protons, divide the number of protons in an atom by the atom's mass number and multiply by 100.

For the isotopes of iridium:

• Iridium-191: The mass percent of protons is calculated as \((77 / 191) \times 100 = 40.3141%\).
• Iridium-193: The mass percent of protons is \((77 / 193) \times 100 = 39.8964%\).

This calculation is crucial in fields like nuclear chemistry and physics, where understanding the composition of an atom is necessary for tasks ranging from determining isotopic abundances to calculating nuclear binding energies.