Question

What is the approximate mass of an oxygen atom in atomic mass units? What is the approximate mass of two oxygen atoms? How about an oxygen molecule?

Short answer

The mass of an oxygen atom is 16 amu. Two oxygen atoms or an \(O_2\) molecule have a mass of 32 amu.

Step-by-step solution

Understand Atomic Mass Units

Atomic mass units (amu) are defined so that carbon-12, which has 6 protons and 6 neutrons, has a mass of exactly 12 amu. Therefore, atomic mass units are often used to express the mass of individual atoms.

Find Mass of One Oxygen Atom

The atomic mass of an oxygen atom is approximately 16 amu. This value is derived from the weighted average of the isotopes of oxygen, but for simplicity, we use 16 amu for a single oxygen atom.

Calculate Mass of Two Oxygen Atoms

To determine the approximate mass of two oxygen atoms, multiply the atomic mass of one oxygen atom by 2. \(\text{mass of two oxygen atoms} = 16 \, \text{amu} \times 2 = 32 \, \text{amu}\)

Calculate Mass of an Oxygen Molecule

An oxygen molecule is represented by \(O_2\). Since an \(O_2\) molecule consists of two oxygen atoms, its mass is the same as the calculated mass of two oxygen atoms: 32 amu.

Key concepts

mass of oxygen atom

The mass of an oxygen atom is typically expressed in atomic mass units (amu), which is a vital concept in chemistry and physics. One atomic mass unit is defined based on the carbon-12 isotope, where one carbon-12 atom is assigned a mass of exactly 12 amu. Therefore, atomic mass units allow scientists to express the mass of atoms in a way that is easier to work with than kilogram measurements.
For a single oxygen atom, its mass is approximately 16 amu. This number accounts for the average mass of naturally-occurring isotopes of oxygen and generally gives a straightforward way to perform calculations with oxygen's atomic mass.

oxygen molecule mass

An oxygen molecule is denoted as \(O_2\), which means it is made up of two oxygen atoms bonded together. To find the mass of an \(O_2\) molecule, we simply need to combine the atomic masses of the two oxygen atoms that make it up. Since each oxygen atom has a mass of about 16 amu, the mass of an \(O_2\) molecule is calculated as follows:
\[\text{mass of two oxygen atoms} = 16 \, \text{amu} \times 2 = 32 \, \text{amu}\]
This calculation shows that the mass of an oxygen molecule is twice that of a single oxygen atom, reflecting the fact that the molecule consists of two atoms.

isotopes of oxygen

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This results in different atomic masses for each isotope.
Oxygen has three stable isotopes, which are:

• \(^{16}O\): With 8 protons and 8 neutrons, this is the most abundant isotope of oxygen.
• \(^{17}O\): This isotope has 8 protons and 9 neutrons.
• \(^{18}O\): This isotope contains 8 protons and 10 neutrons.

These isotopes contribute to the weighted average atomic mass of oxygen, which is typically calculated to be close to 16 amu. Despite these different isotopes, when calculating average atomic masses for practical purposes, \(^{16}O\) is often the primary focus due to its abundance in nature.