Question

An isotope of sodium (Na) has a mass number of 22 . How many neutrons does it have? a. 11 b. 12 C. 22 d. 44

Short answer

The sodium isotope with a mass number of 22 has 11 neutrons (a).

Step-by-step solution

Recall the formula for finding the number of neutrons

The formula for finding the number of neutrons in an element is: Number of neutrons = mass number - atomic number

Identify the input values

In this exercise, we have the mass number (A) and the atomic number (Z) as: Mass number (A) = 22 (given for the sodium isotope) Atomic number (Z) = 11 (sodium's atomic number)

Calculate the number of neutrons using the formula

Now, use the formula for the number of neutrons using the given values: Number of neutrons = mass number - atomic number Number of neutrons = 22 - 11

Find the correct answer

Now, calculate the value: Number of neutrons = 11 So, the sodium isotope with a mass number of 22 has 11 neutrons. The correct answer is (a) 11.

Key concepts

Atomic Structure

At the heart of nuclear chemistry is the atomic structure, which defines an atom by its composition. An atom consists of three main particles: protons, neutrons, and electrons. These particles contribute to the identity and behavior of each element.
Protons and neutrons are bound tightly in the nucleus, forming the atom's core. Protons have a positive charge, while neutrons are neutral, having no charge. The nucleus is where most of the atom's mass is concentrated.

• Protons determine the atomic number, which is unique for each element.
• Electrons are negatively charged particles that orbit around the nucleus in energy levels or shells.
• The number of electrons equals the number of protons in a neutral atom, balancing the overall charge.

The distribution and balance of these particles within the atom's structure are crucial to many chemical properties and behavior of the element.

Isotopes

While exploring atomic structure, the concept of isotopes plays a pivotal role. Isotopes are different forms of the same element that have the same number of protons but differ in the number of neutrons.
This variation in neutron number leads to differences in mass number between isotopes.

Key Characteristics of Isotopes:

• Isotopes share the same atomic number but have different mass numbers.
• They can exhibit differences in stability and radioactivity.
• Some isotopes occur naturally, while others are synthetically produced.

For example, the isotope of sodium mentioned in the exercise differs from typical sodium due to having a different mass number. Such differences can affect physical properties, like atomic mass, but the chemical properties remain primarily due to the unchanged number of protons and electrons.

Neutrons

Neutrons are vital components of the nucleus, influencing both the stability and mass of an atom. Unlike charged particles, neutrons are neutral, meaning they carry no electric charge. Despite lacking charge, they play a significant role in nuclear reactions and isotopic behavior.
Neutrons impact an element's isotopic identity because they vary among isotopes while the number of protons remains constant.

Importance of Neutrons:

• They help mitigate the repulsive forces between protons in the nucleus.
• Neutrons contribute to an atom's mass number, essential for identifying isotopes.
• They are key players in nuclear processes, such as fission and fusion.

The number of neutrons can be found using the formula: \[\text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number}\]This formula was used in the exercise to find the number of neutrons in a sodium isotope, illustrating how neutrons distinguish isotopes of the same element.