Problem 28 - Chemistry The Central Science

Question

Each of the following isotopes is used in medicine. Indicate the number of protons and neutrons in each isotope: (a) phosphorus-32,(b) chromium-51, (c) cobalt--60, (d) technetium-99, (e) iodine-131, (f) thallium-201.

Step-by-Step Solution

Answer

The number of protons and neutrons in each isotope are as follows: (a) Phosphorus-32: 15 protons and 17 neutrons (b) Chromium-51: 24 protons and 27 neutrons (c) Cobalt-60: 27 protons and 33 neutrons (d) Technetium-99: 43 protons and 56 neutrons (e) Iodine-131: 53 protons and 78 neutrons (f) Thallium-201: 81 protons and 120 neutrons

Step 1: Look up the Atomic Numbers

Using a periodic table, find the atomic number (number of protons) for each element: (a) Phosphorus (P) - Atomic Number: 15 (b) Chromium (Cr) - Atomic Number: 24 (c) Cobalt (Co) - Atomic Number: 27 (d) Technetium (Tc) - Atomic Number: 43 (e) Iodine (I) - Atomic Number: 53 (f) Thallium (Tl) - Atomic Number: 81

Step 2: Find the Number of Neutrons in Each Isotope

Subtract the atomic number from the mass number (isotope number) to find the number of neutrons: (a) Phosphorus-32: 32 - 15 = 17 neutrons (b) Chromium-51: 51 - 24 = 27 neutrons (c) Cobalt-60: 60 - 27 = 33 neutrons (d) Technetium-99: 99 - 43 = 56 neutrons (e) Iodine-131: 131 - 53 = 78 neutrons (f) Thallium-201: 201 - 81 = 120 neutrons

Step 3: Write the Final Answer

Present the number of protons and neutrons for each isotope: (a) Phosphorus-32: 15 protons and 17 neutrons (b) Chromium-51: 24 protons and 27 neutrons (c) Cobalt-60: 27 protons and 33 neutrons (d) Technetium-99: 43 protons and 56 neutrons (e) Iodine-131: 53 protons and 78 neutrons (f) Thallium-201: 81 protons and 120 neutrons

Key Concepts

Atomic Number

The atomic number is a fundamental property of an element, representing the number of protons found in the nucleus of an atom. This number is unique to each element and determines its identity and position in the periodic table. For instance, phosphorus has an atomic number of 15, meaning every phosphorus atom has 15 protons.

• Helps identify the element
• Equals the number of protons
• Defines the element's position in the periodic table

In terms of isotopes, the atomic number remains unchanged even though the mass number (sum of protons and neutrons) may vary. For example, phosphorus-32 and phosphorus-31 are isotopes, but both have the same atomic number of 15. The differing factor is the number of neutrons, which affects the atomic mass.

Protons

Protons are positively charged particles located in the nucleus of an atom. They are one of the primary components that make up an atom's overall structure. The number of protons directly corresponds to the atomic number of an element and thus determines the element's identity. For example, chromium has 24 protons, as indicated by its atomic number of 24.

• Positively charged
• Located in the atom's nucleus
• Dictates the element's identity

Protons also play a vital role in the stability and chemical behavior of an atom. The attraction between protons and electrons (negatively charged particles) results in the atom's overall neutral charge. Understanding proton count is crucial when considering different isotopes, as, for any isotope of a given element, the number of protons remains constant while the number of neutrons can vary.

Neutrons

Neutrons are neutral particles situated within the atomic nucleus, and unlike protons, they do not carry any electric charge. They play a crucial role in the stability of an atom. While protons determine the identity of an element, neutrons influence the isotope and mass stability.

• Neutral charge
• Located in the nucleus
• Influences atomic mass and stability

Neutrons allow for the existence of isotopes, where atoms of the same element have different numbers of neutrons, resulting in different mass numbers. For example, iodine-131 has 78 neutrons compared to iodine-127, which is more commonly occurring in nature. This difference in neutron count can affect the stability and radioactive properties of isotopes, making them sometimes useful in medical and industrial applications.