Problem 92 - Introductory Chemistry Atoms First

Question

A student claims that isotopes of the same element have the same number of neutrons but different numbers of protons. Is he correct? Justify your answer.

Step-by-Step Solution

Answer

The student's claim is incorrect. Isotopes of the same element have the same number of protons but different numbers of neutrons, which affects their atomic mass.

Step 1: Understanding isotopes

Isotopes are atoms of the same element that have the same number of protons, but different numbers of neutrons. The primary difference among isotopes is their mass, which comes from the differing numbers of neutrons in the nucleus of the atoms.

Step 2: Evaluating the student's claim

The student claims that isotopes of the same element have the same number of neutrons but different numbers of protons. This statement contradicts the definition of isotopes, which states that isotopes have the same number of protons but different numbers of neutrons.

Step 3: Drawing a conclusion

The student's claim is incorrect. Isotopes of the same element have the same number of protons, but different numbers of neutrons. The difference in the number of neutrons is what distinguishes isotopes of the same element, as it affects their atomic mass.

Key Concepts

Atomic Structure

Atomic structure refers to the composition of an atom, which is the fundamental unit of matter. Each atom is made up of three main particles: protons, neutrons, and electrons. These particles play distinct roles in the atom:

• Protons and neutrons form the nucleus of the atom, which is the central part.
• Electrons orbit around the nucleus in regions called electron shells.

The behavior and arrangement of these particles determine the properties of an atom. This arrangement also explains why atoms of the same element can exist in different forms or isotopes. Understanding atomic structure is essential for exploring the variability and chemistry of elements.

Protons

Protons are positively charged particles found in the nucleus of an atom. They play a crucial role in defining the identity of an element as they determine the atomic number. The atomic number is the number of protons in an atom and is unique to each element:

• For example, all hydrogen atoms have one proton, so hydrogen's atomic number is 1.
• Oxygen atoms have eight protons, making its atomic number 8.

Protons also contribute to the mass of an atom but remain constant for isotopes of a given element. This means isotopes of the same element have the same number of protons, which is central to distinguishing isotopes correctly.

Neutrons

Neutrons are neutral particles, meaning they carry no charge, and they are also located in the nucleus of an atom. The number of neutrons in an atom can vary even among atoms of the same element. This variability is what leads to different isotopes:

• The number of neutrons does not affect the chemical behavior of the atom, as it is the protons that define the element.
• However, varying number of neutrons affects the mass of an atom, thus producing isotopes.

For instance, while carbon-12 and carbon-14 are both isotopes of carbon, carbon-12 has six neutrons, and carbon-14 has eight neutrons. Understanding the role of neutrons is critical to grasping why isotopes exist and how they differ.

Atomic Mass

Atomic mass is the total mass of an atom, primarily determined by the combined number of protons and neutrons. Electrons contribute very little to the atomic mass due to their relatively negligible mass. The atomic mass varies in isotopes of the same element because of differences in the number of neutrons:

• Isotopes are often referenced by their atomic mass, such as uranium-235 and uranium-238, which differ due to a different neutron count.
• The atomic mass is frequently expressed in atomic mass units (amu), where one amu is roughly the mass of one nucleon (either a proton or a neutron).

Understanding how atomic mass is calculated and its significance helps explain why isotopes exist and how they can be applied in fields like chemistry and physics. Atomic mass can be a key factor in radioactive decay or the stability of an atom.