Problem 8 - Chemistry and Chemical Reactivity

Question

Atomic structure. (a) The synthetic radioactive element technetium is used in many medical studies. Give the number of electrons, protons, and neutrons in an atom of technetium-99. (b) Radioactive americium-241 is used in household smoke detectors and in bone mineral analysis. Give the number of electrons, protons, and neutrons in an atom of americium-241.

Step-by-Step Solution

Answer

Technetium-99: 43 protons, 43 electrons, 56 neutrons. Americium-241: 95 protons, 95 electrons, 146 neutrons.

Step 1: Understanding Atomic Number and Atomic Mass

For any element, the atomic number tells us the number of protons, which is also equal to the number of electrons in a neutral atom. For technetium (Tc), the atomic number is 43. For americium (Am), the atomic number is 95.

Step 2: Analyzing Technetium-99

Technetium-99 has a mass number of 99. The mass number is the sum of protons and neutrons in an atom. Therefore, to find the number of neutrons: \[\text{Mass number} = \text{Protons} + \text{Neutrons}\] \[99 = 43 + \text{Neutrons} \] Thus, \[ \text{Neutrons} = 99 - 43 = 56 \] Technetium-99 has 43 protons, 43 electrons, and 56 neutrons.

Step 3: Analyzing Americium-241

Americium-241 has a mass number of 241. Using the same method: \[\text{Mass number} = \text{Protons} + \text{Neutrons}\] \[241 = 95 + \text{Neutrons}\] Therefore, \[ \text{Neutrons} = 241 - 95 = 146 \] Americium-241 has 95 protons, 95 electrons, and 146 neutrons.

Key Concepts

Atomic Number

The atomic number is a fundamental property of an element. It denotes the number of protons found in each atom of that element. Since protons are positively charged, the atomic number also equals the number of electrons in a neutral atom, maintaining electrical neutrality. This means, for technetium, the atomic number is 43, signifying it has 43 protons and 43 electrons. Similarly, americium has an atomic number of 95, indicating 95 protons and a matching 95 electrons.
Understanding atomic numbers helps in identifying the element, as each element in the periodic table has a unique atomic number:

• The atomic number of technetium is 43.
• The atomic number of americium is 95.

This concept forms the basis of the periodic table, arranging elements in increasing order of their atomic numbers. This order reveals periodic tendencies in properties among elements.

Mass Number

The mass number is key to understanding the basic structure of atoms. This number represents the sum of protons and neutrons in an atom's nucleus. Electrons are not included in the mass number due to their relatively negligible mass.
For technetium-99, the mass number is 99. By subtracting the atomic number (number of protons), we can find the number of neutrons:

• Number of neutrons in technetium-99: 99 (mass number) - 43 (protons) = 56 neutrons.

Similarly, for americium-241, the mass number is 241:

• Number of neutrons in americium-241: 241 (mass number) - 95 (protons) = 146 neutrons.

Both protons and neutrons contribute significantly to an atom’s mass, helping define its isotopic identity. Different isotopes of an element have the same number of protons, but vary in neutron count, hence differing in mass number.

Radioactive Isotopes

Radioactive isotopes, or radioisotopes, are atoms with unstable nuclei that release radiation as they convert to a more stable form. This characteristic is vital in many fields, including medicine and archaeology.
Technetium-99 is a synthetic isotope used extensively in medical imaging. Its radioactive nature allows for clear imaging in diagnostic procedures. Americium-241, on the other hand, is naturally radioactive and is widely used in household smoke detectors. It releases alpha particles, which aid smoke detection due to their interaction with smoke particles.

• Radioactive isotopes have unique applications due to their energy release.
• They help in diverse areas such as medical diagnosis and safety devices.

The decay rate of radioisotopes, often measured as half-life, determines how long these elements can remain active. The understanding of radioactive isotopes better equips us to utilize them safely and effectively across various industries.