Problem 61 - Chemistry Matter and Change

Question

How can you determine the number of neutrons in an atom if its mass number and its atomic number are known.

Step-by-Step Solution

Answer

To determine the number of neutrons (N) in an atom with a given mass number (A) and atomic number (Z), simply subtract the atomic number from the mass number: \( N = A - Z \). Ensure the result is a whole number and non-negative.

Step 1: Identify mass number and atomic number

Use the given information to identify the mass number (A) and the atomic number (Z).

Step 2: Calculate the number of neutrons

To find the number of neutrons (N) in the atom, subtract the atomic number (Z) from the mass number (A): \[ N = A - Z \]

Step 3: Verify your result

Make sure that the calculated number of neutrons is a whole number and non-negative.

Key Concepts

neutrons

Neutrons are subatomic particles that reside in the nucleus of an atom along with protons. While protons carry a positive charge, neutrons are neutral and have no electrical charge. They serve an important role in providing stability to an atom's nucleus.
Without neutrons, protons in the nucleus would repel each other due to their positive charges, leading to nuclear instability. Understanding the number of neutrons aids in understanding an isotope of an element. Isotopes have the same number of protons, but different numbers of neutrons.

• Neutrons contribute to the atomic mass but do not affect the chemical charge of the atom.
• Their number can change even in the same element, resulting in isotopes.

To calculate neutrons, you subtract the atomic number from the mass number, as shown in the original solution. Make sure your result is always a whole number, since you can't have a fraction of a neutron.

mass number

The mass number is a total count of the number of protons and neutrons in an atom's nucleus. Unlike the atomic number, which only counts protons, the mass number reflects the overall size of the atom's core.It is represented by the symbol 'A' in the periodic table. This number is a whole number since it represents a sum of particles that don't have fractional components.

• Mass number is crucial for differentiating between isotopes: isotopes have the same atomic number but different mass numbers.
• The formula for mass number is: \[ A = Z + N \] where \( Z \) is the atomic number and \( N \) is the number of neutrons.

When looking at the periodic table, the mass number is not always displayed, but it can be inferred by knowing the atomic number and the common isotopes for an element. This helps in determining whether isotopes or variations in neutron numbers exist.

atomic number

The atomic number, represented by the symbol 'Z,' is one of the fundamental characteristics of an element. It indicates the number of protons in the nucleus of an atom. This number is unique for each element and is key to an element's identity on the periodic table.

• Every atom of a given element has the same number of protons, thus the same atomic number.
• The atomic number determines the chemical properties of an atom and its place in the periodic table.

The atomic number does not change, even if the atom gains or loses neutrons (forming isotopes) or changes its mass. In the original problem, it was essential for calculating the number of neutrons, as it acts as a reference from which the mass number is subtracted.