Question

Find the symbol for chlorine on the periodic table. a) How does the number given just below the symbol for chlorine (rounded to \(0.01\) ) compare with the average mass (amu) of one chlorine atom? b) How does the number given just below the symbol for chlorine (rounded to 0.01) compare with the mass (grams) of \(6.022 \times 10^{23}\) chlorine atoms?

Short answer

a) The number given below the symbol for chlorine on the periodic table is the same as the average mass of one chlorine atom when both are rounded to 0.01. They are both 35.45. b) The number given below the symbol for chlorine on the periodic table is the same as the mass of \(6.022 \times 10^{23}\) chlorine atoms when rounded to 0.01. They both are 35.45, but the latter is in grams.

Step-by-step solution

Understanding Atomic Mass

Atomic mass is the weight of one atom of an element, which is usually located just below the symbol of an element on the periodic table. It's often close to the mass number of the element. For chlorine, you will find the rounded atomic mass to be 35.45 amu (atomic mass units). This number indicates the average mass of all isotopes of chlorine, factoring in their relative natural abundances.

Comparison with Average Mass of a Chlorine Atom

The number displayed below the chlorine symbol on the periodic table is the atomic mass. So in part a), essentially we are asked to compare the atomic mass with itself. Therefore, they are the same, given the atomic mass is the average mass of one chlorine atom.

Understanding Avogadro's Number and Molar mass

Avogadro's number (\(6.022 \times 10^{23}\)) is the number of atoms present in one mole of an element. Its unit is atoms/mole. The molar mass of an element is the mass of one mole of the element, which is equal to the atomic mass but expressed in grams per mole (g/mol). For chlorine, this number is also 35.45 but the unit is g/mol.

Calculate Mass of Avogadro's Number of Chlorine Atoms

In part b), we are asked to compare the atomic mass with the mass of \(6.022 \times 10^{23}\) chlorine atoms, which is essentially one mole of chlorine atoms. Therefore, the mass in grams of \(6.022 \times 10^{23}\) chlorine atoms is 35.45 g, which is the mass of one mole of chlorine. This is equal to the atomic mass, albeit with a different unit.

Key concepts

Atomic Mass

The atomic mass is a fundamental concept in chemistry. It represents the average mass of an atom of an element, taking into account all its naturally occurring isotopes. These isotopes vary in mass slightly due to the different numbers of neutrons they contain.

• Atomic mass is measured in atomic mass units (amu), and it reflects the weighted average of the isotopes of the element.
• For example, the atomic mass of chlorine is approximately 35.45 amu.
• It is the number you will find just below the symbol of the element on the periodic table.

Atomic mass provides insight into the abundance of an element's isotopes. It's crucial for calculating the masses of atoms in a sample of an element.

Chlorine Atom

Chlorine is a chemical element with the symbol Cl and atomic number 17. It is part of the halogen group in the periodic table and is commonly found in nature as a gas.

• Chlorine has two stable isotopes: Cl-35 and Cl-37.
• The more abundant isotope, Cl-35, contributes more significantly to chlorine's average atomic mass.
• These isotopes' varying abundances are the reason for the non-integer atomic mass value, seen as 35.45 amu.

Understanding the isotopic composition of a chlorine atom helps chemists in various reactions and processes involving chlorine, from manufacturing to everyday applications.

Avogadro's Number

Avogadro's number is a key figure in chemistry that provides the bridge between the atomic scale and the gram scale. It is defined as the number of atoms or molecules in one mole of a substance.

• Avogadro's number is approximately \(6.022 \times 10^{23}\).
• This massive number allows chemists to count atoms by weighing out equal amounts in grams to the atomic or molecular mass in amu.

Having Avogadro's number helps simplify calculations in chemistry, enabling the use of "moles" as a practical unit for measuring chemical quantities. It makes it easier to relate measurements at the microscopic level to the macroscopic world.

Molar Mass

Molar mass is the weight of one mole of a substance, which is directly tied to Avogadro's number. It provides the link between mass in grams and the number of moles or particles present.

• For any element, the molar mass in grams per mole (g/mol) is numerically equal to its atomic mass.
• For chlorine, the molar mass is 35.45 g/mol, the same number as its atomic mass but in different units.
• Molar mass indicates the mass contained in a mole of atoms, which corresponds to Avogadro's number of particles.

This measurement is a central concept in chemical science, often used in calculating reactant and product quantities in chemical reactions, ensuring the correct distribution of atoms and molecules.