Problem 1 - Chemistry An Atoms First Approach

Question

Although the earth was formed from the same interstellar material as the sun, there is little elemental hydrogen \(\left(\mathrm{H}_{2}\right)\) in the earth's atmosphere. Explain.

Step-by-Step Solution

Answer

In short, the Earth's atmosphere has little elemental hydrogen (\(\mathrm{H}_{2}\)) due to the Earth's weaker gravitational force compared to the Sun, hydrogen's low molecular weight, and chemical reactions occurring in the Earth's atmosphere that involve hydrogen. These factors cause hydrogen to escape into space and form compounds with other elements, resulting in its limited presence in the Earth's atmosphere.

Step 1: Understand the components of the Earth and the Sun

The Earth and the Sun were indeed formed from the same interstellar material, but their compositions today are quite different. The Sun is primarily composed of hydrogen and helium, while the Earth has a more diverse composition. Hydrogen gas, which is composed of two hydrogen atoms combined to form \(\mathrm{H}_{2}\), is the most abundant element in the universe, so it's relevant to consider why it's not so abundant in the Earth's atmosphere.

Step 2: Analyze gravitational forces

The Earth has a weaker gravitational force compared to the Sun due to its smaller mass. The Sun's large mass allows it to maintain a strong gravitational pull that keeps lighter elements, such as hydrogen and helium, from escaping into space. The Earth's weaker gravitational force makes it more difficult for it to retain lighter elements in its atmosphere.

Step 3: Hydrogen's low molecular weight

Hydrogen has the lowest molecular weight of all elements, which means that it has a higher tendency to escape the Earth's gravitational pull and leak into space. Due to this, lighter elements like hydrogen are more likely to escape from the Earth's atmosphere compared to heavier elements.

Step 4: Chemical reactions in the Earth's atmosphere

Another reason for the absence of significant amounts of elemental hydrogen in the Earth's atmosphere is due to various chemical reactions occurring within the atmosphere itself. Hydrogen can easily react with other elements, resulting in the formation of water (\(H_2O\)) and various other compounds. As a result, the amount of free hydrogen gas is continuously reduced in the Earth's atmosphere.

Step 5: Conclusion

In summary, there is little elemental hydrogen present in the Earth's atmosphere because of the following factors: the Earth's weaker gravitational force compared to the Sun, hydrogen's low molecular weight, and chemical reactions occurring in the Earth's atmosphere that involve hydrogen. It is due to these reasons that the amounts of elemental hydrogen in the atmospheres of Earth and the Sun are significantly different, even though they were both formed from the same interstellar material.