What is the mass in grams of a single atom of each of the following elements? (a) As, (b) Ni.

Understanding Avogadro's number is key to unlocking the relationship between atoms and mass in chemistry. It is the number of units (usually atoms or molecules) in one mole of a substance. Avogadro's number is a constant and is approximately equal to \(6.022 \times 10^{23}\) units per mole. This large number allows chemists to work with the macroscopic quantities of substances that can be seen and measured, while still referring to the microscopic scale of atoms and molecules.

When doing calculations involving substances at the atomic or molecular level, Avogadro's number becomes crucial. To find the mass of a single atom, as in our exercise, one would divide the molar mass of the element by Avogadro's number. This relationship allows for the connection between observable quantities of materials (measured in grams) and the number of atoms or molecules those quantities contain.

The concept of molar mass is fundamental in chemistry for converting between the mass of a material and the number of moles in that mass. The molar mass of an element is the mass in grams of one mole of that element. The unit for molar mass is grams per mole (g/mol). It can be seen as the bridge between the microscopic world of atoms and the macroscopic world we experience every day.

For instance, the molar mass of arsenic (As) is 74.92 g/mol and nickel (Ni) is 58.69 g/mol. This means one mole of arsenic weighs 74.92 grams, and similarly, one mole of nickel weighs 58.69 grams. Each mole of these elements contains Avogadro's number of atoms. Dividing the molar mass by Avogadro's number, as shown in the solution for the exercise, provides the mass of a single atom in grams. This direct calculation is particularly useful in the field of chemistry to relate a material's mass to its atomic or molecular composition.

The Periodic Table of Elements is a cornerstone of the field of chemistry, providing a systematic visual representation of all known elements. It not only displays the elements but also contains essential information about them, such as atomic number, atomic mass, and much more. Each element's atomic mass, which is closely related to its molar mass, can be found on the Periodic Table and is vital for calculating atomic and molecular weights.

Using the Periodic Table, students can easily determine the molar mass required to perform calculations like discovering the mass of individual atoms. In the exercise provided, molar mass values for arsenic and nickel were obtained directly from the Periodic Table to facilitate the subsequent steps. Understanding how to locate and utilize this information on the Periodic Table is a fundamental skill for anyone studying chemistry.