Question

If you select one carbon atom at random, the mass of that atom is most likely to be ______ amu.

Short answer

The most likely mass of a carbon atom is 12 amu.

Step-by-step solution

Consider the Most Common Isotope of Carbon

First, note that the most common isotope of a Carbon atom is Carbon-12. An isotope is a variant of a particular chemical element, which differs in the number of neutrons. For Carbon, its most common and stable isotope is Carbon-12.

Understand Atomic Mass Units

The mass of an atom is measured in atomic mass units (amu). The atomic mass is roughly equivalent to the number of protons and neutrons contained in the atom. Carbon-12 has 6 protons and 6 neutrons, thus it has a mass of approximately 12 amu.

Answer the Most Likely Atom Mass

Because Carbon-12 is the most common isotope of carbon, if a carbon atom is selected at random, it is most likely to be a Carbon-12 atom. Therefore, the mass of the atom is most likely to be 12 amu.

Key concepts

Isotopes

Isotopes are variations of elements that have the same number of protons but differ in the number of neutrons. This difference in neutron count results in atoms of the same element having different masses. For instance, carbon has several isotopes, such as Carbon-12, Carbon-13, and Carbon-14, where the numbers represent the total mass of protons and neutrons in the nucleus. In nature, these isotopes occur in varying abundances, with Carbon-12 being the most abundant isotope of carbon.

Understanding isotopes is crucial because they have different properties and can be used in various practical applications. For example, Carbon-14 is used in radiocarbon dating to determine the age of ancient artifacts. Despite their different masses, isotopes of an element exhibit very similar chemical behaviors because they have the same number of protons and electrons, which are responsible for chemical reactions.

Atomic Mass

Atomic mass refers to the mass of an atom, typically expressed in atomic mass units (amu). In an atom, the bulk of the mass comes from the protons and neutrons in the nucleus, with each proton or neutron approximately equal to 1 amu. The atomic mass of an element is often close to the mass number of its most stable isotope. However, because elements can exist as a mixture of isotopes, the atomic mass usually reflects an average that accounts for the different isotopes and their natural abundances.

For example, carbon has an atomic mass of about 12.011 amu, which is a weighted average of its isotopes, including Carbon-12, Carbon-13, and the trace amounts of Carbon-14 present.

Carbon-12

Carbon-12 is the most common isotope of carbon and serves as the standard by which atomic masses of all other elements are defined. It contains 6 protons and 6 neutrons, amounting to a total mass of 12 amu. Due to its stable nature and ample presence, Carbon-12 is used in defining the atomic mass unit. One amu is conventionally defined as one-twelfth of the mass of a Carbon-12 atom.

This standardization helps in achieving consistency in measurements across chemistry and physics. The choice of Carbon-12 as the reference point was made based on its stable presence in nature and the ability to create precise measurements of its mass, making it an essential element in the study of atomic structures.