Question

Lithium has two stable isotopes, lithium-6 with an atomic mass of \(6.0151 \mathrm{u}\) and lithium- 7 with an atomic mass of \(7.0160 \mathrm{u}\). Predict which of these two isotopes is more common by looking at the atomic mass from the periodic table. Explain your reasoning.

Short answer

Lithium-7 is more common because its atomic mass is closer to the average atomic mass of lithium on the periodic table.

Step-by-step solution

- Identify the isotopes and their masses

There are two stable isotopes of lithium: lithium-6 with an atomic mass of 6.0151 u and lithium-7 with an atomic mass of 7.0160 u.

- Find the atomic mass from the periodic table

Look up lithium on the periodic table to determine its atomic mass. The periodic table shows the average atomic mass for lithium is approximately 6.94 u.

- Compare the periodic table mass with isotope masses

Compare the average atomic mass (6.94 u) with each isotope's mass: 6.0151 u for lithium-6 and 7.0160 u for lithium-7.

- Compare the closeness of values

Notice that the average atomic mass (6.94 u) is much closer to the mass of lithium-7 (7.0160 u) than to lithium-6 (6.0151 u).

- Make the prediction

Since the average atomic mass from the periodic table is closer to lithium-7, it indicates that lithium-7 is more abundant than lithium-6.

- Concluding statement

Conclude that lithium-7, with an atomic mass of 7.0160 u, is the more common isotope.

Key concepts

Atomic Mass

The atomic mass of an element is an essential concept in chemistry. It represents the weighted average mass of the atoms in a chemical element, and it's measured in atomic mass units (u). This value factors in all of the isotopes of that element and their relative abundances. For example, lithium's average atomic mass is approximately 6.94 u. This value is calculated by averaging the atomic masses of lithium's isotopes, lithium-6 and lithium-7, according to their abundances.

Stable Isotopes

Isotopes are atoms of the same element that have different numbers of neutrons. This difference in neutrons results in different atomic masses. Chemical elements often have one or more stable isotopes, which do not undergo radioactive decay over time. For lithium, there are two stable isotopes: lithium-6, with an atomic mass of 6.0151 u, and lithium-7, with an atomic mass of 7.0160 u.
To determine which isotope is more prevalent naturally, we look at the average atomic mass provided in the periodic table. Since this value represents the combined average of the different isotopes based on their natural occurrence, a higher approximation to the atomic mass indicates a higher abundance. In lithium's case, the average atomic mass is 6.94 u, closer to lithium-7, indicating it is the more abundant isotope in nature.

Periodic Table

The periodic table is a comprehensive chart that organizes the chemical elements based on their properties. Each element is represented by its chemical symbol and includes crucial information like atomic number and atomic mass. When you look up lithium on the periodic table, you'll see its symbol (Li), atomic number (3), and the average atomic mass (~6.94 u). This average atomic mass is vital as it reflects the element's natural isotopic distribution.
The periodic table is a fundamental tool in chemistry. It provides insights into the elemental properties and helps predict how elements will react with one another. Through detailed examination of the periodic table, you can glean a wealth of information about the building blocks of matter, such as isotope prevalence and elemental abundances.