DoAssignment.ca
F3.1 · Identify major and minor components of Earth’s atmosphere
Learn to identify major and minor components of earth’s atmosphere through clear examples and targeted practice.
Ontario Grade 11 Chemistry
Gases and Atmospheric Chemistry
Identifying its major and minor components | Study topic F3.1
Air is all around us, but most of it is invisible. A breeze can move leaves, and a balloon can expand when filled with air. These familiar observations show that air is matter, even though we cannot see most of its particles. Earth’s atmosphere is the layer of gases around the planet. In this lesson, you will identify the gases that make up most of the atmosphere and those present in much smaller amounts. The proportions given are approximate, because some components vary with location and conditions.
What you will learn
- Identify the major and minor components of Earth’s atmosphere.
- Describe the approximate proportions of the main gases in dry air.
- Explain why water vapour is described as a variable component.
1. From air we observe to a mixture of gases
Before describing air, recall two ideas about matter. Matter has mass and takes up space. A gas is a state of matter whose particles are spread out and move freely. Air can therefore take up space, such as inside a balloon, even though individual gas particles are too small to see.
The atmosphere is not a single gas. It is a mixture: a combination of substances present together without being one pure substance. In the particle model, air contains many different kinds of gas particles moving among one another. The atmosphere is held around Earth by gravity, but the main idea here is its composition: which gases are present and how much of the mixture each makes up.
A percentage is a way to describe a part out of one hundred. When atmospheric composition is reported by volume, the percentage estimates the share of the gas mixture occupied by each gas. For gases in air, this is a useful way to compare their amounts. It does not mean that each small sample must contain exactly the same count of every kind of particle.
- Air is a mixture of gases, not a single pure substance.
- A gas’s percentage by volume describes its share of the gas mixture.
- The reported proportions are approximate.
2. Major components of dry air
The two major components of dry air are nitrogen and oxygen. “Major” means present in a large proportion compared with the other components. Nitrogen makes up about 78% of dry air. Oxygen makes up about 21%. Together, these two gases account for about 99% of dry air.
The chemical formula for a nitrogen gas particle is . Each particle contains two nitrogen atoms. Oxygen gas particles have the formula , with two oxygen atoms in each particle. These formulas describe the particles; they do not change the approximate percentages in the air.
Argon is another component, but it is present in a much smaller amount: about 0.93% of dry air. It is still more abundant than many other gases in the atmosphere. Carbon dioxide is also a minor component. Its proportion is only about 0.04% in commonly used approximate composition figures, though its amount changes over time. The word “minor” does not mean unimportant; it means that the component makes up a small fraction of the mixture.
“Dry air” means air considered without water vapour. This makes it easier to compare the fairly steady proportions of its main gases. In real air, the amount of water vapour varies. It can be much greater in humid conditions than in dry conditions, so it is usually identified separately rather than assigned one fixed percentage for all places and times.
- Nitrogen and oxygen are the major components of dry air.
- Argon and carbon dioxide are minor components.
- Dry-air percentages exclude water vapour.
3. Minor components and reading composition information
Minor components occur in smaller proportions than nitrogen and oxygen. Examples include argon, carbon dioxide, neon, helium, methane, krypton, hydrogen, and ozone. These gases are not all present in equal amounts. Some are present in extremely small amounts. Water vapour is another component of the atmosphere, but unlike the approximate dry-air percentages, its proportion varies considerably.
A composition list can be read by comparing each percentage. A larger percentage means a larger share of the mixture. A percentage far below one percent indicates a minor component. Keep the reference mixture in mind: a percentage for dry air does not include water vapour, while a description of actual air may include it.
The percentages in a list may not add to exactly 100% if each value has been rounded. That does not mean the atmosphere contains an unidentified gas equal to the difference. Rounding changes the displayed values slightly. Also, a tiny percentage can still describe a real component. “Minor” refers to the amount, not whether the gas exists.
- Minor gases are present in small proportions; examples include argon and carbon dioxide.
- Water vapour varies, so its proportion is not fixed in the same way as the main dry-air components.
- Rounded percentages may not total exactly 100%.
4. A method for identifying major and minor components
When you are given an atmospheric-composition list, first check whether it describes dry air or includes water vapour. Next, identify the largest percentages. Those gases are the major components. Then compare the remaining percentages with them. Much smaller shares belong to minor components. Finally, keep approximate values and rounding in mind.
This method uses relative amount, not a judgement about importance. For example, nitrogen is a major component because it makes up most of dry air. Carbon dioxide is a minor component because it makes up a very small share. Both are components of the atmosphere. The task in F3.1 is to identify them by their amounts, not to explain their effects or how they change.
Use chemical formulas only when useful to name a gas particle. Nitrogen gas is , oxygen gas is , and carbon dioxide is . The subscript tells how many atoms of that element occur in one particle. The percentages describe the mixture, while the formulas describe the particles. These are different kinds of information.
- Check what the stated composition includes.
- Use relative percentages to distinguish major from minor components.
- A chemical formula identifies a particle; a percentage describes its share of the mixture.
Approximate composition of dry air
| Component | Approximate proportion | Classification |
|---|---|---|
| Nitrogen | 78% | Major |
| Oxygen | 21% | Major |
| Argon | 0.93% | Minor |
| Carbon dioxide | 0.04% | Minor |
| Other trace gases | Small amounts | Minor |
Worked example
Classifying gases in a composition list
A simplified description of dry air lists nitrogen at about 78%, oxygen at about 21%, argon at about 0.93%, and carbon dioxide at about 0.04%. Identify the major and minor components, and explain how you decided.
- Check the basisThe list describes dry air, so water vapour is not included. Compare the gases using the listed approximate percentages.
- Find the largest sharesNitrogen and oxygen have percentages much larger than the other listed gases. They are the major components. 78% and 21%
- Classify the smaller sharesArgon and carbon dioxide each make up less than one percent, so they are minor components in this list. Argon’s share is larger than carbon dioxide’s, but both are minor compared with nitrogen and oxygen. 0.93% and 0.04%
Answer: The major components are nitrogen and oxygen. The minor components listed are argon and carbon dioxide.
Check: The two largest amounts are assigned to the major components, and both smaller amounts are identified as minor. These are approximate values for dry air.
Common mistakes and how to avoid them
Calling oxygen the most abundant gas in air.
Correction: Nitrogen is the most abundant gas in dry air, at about 78%. Oxygen is second, at about 21%.
Treating water vapour as having one fixed percentage in all air.
Correction: Water vapour varies with conditions. Dry-air composition figures leave it out.
Assuming minor means unimportant or absent.
Correction: Minor means present in a smaller proportion. A minor component is still present in the atmosphere.
Confusing a gas formula with its percentage.
Correction: A formula such as describes a particle. A percentage such as 21% describes the gas’s approximate share of dry air.
Lesson summary
- Earth’s atmosphere is a mixture of gases.
- Nitrogen, about 78%, and oxygen, about 21%, are the major components of dry air.
- Argon, carbon dioxide, and other gases are minor components because their proportions are much smaller.
- Water vapour is present in the atmosphere but varies, so dry-air composition excludes it.
- Percentages are approximate and may be rounded.
Check your understanding
Question 1
Which pair makes up most of dry air?
- Nitrogen and oxygen
- Argon and carbon dioxide
- Oxygen and helium
- Water vapour and methane
Show answer and explanation
Nitrogen and oxygen
Nitrogen and oxygen are the two major components, at about 78% and 21% of dry air.
Question 2
Why is water vapour usually described separately from fixed dry-air percentages?
- It is not a gas.
- Its proportion varies.
- It is the most abundant component of dry air.
- It is not part of the atmosphere.
Show answer and explanation
Its proportion varies.
Water vapour is a gas in the atmosphere, but its proportion varies with conditions.
Question 3
A gas is listed as 0.04% of dry air. How should it be classified by amount?
- Major component
- Minor component
- Not a component
- The same amount as nitrogen
Show answer and explanation
Minor component
A proportion of 0.04% is much smaller than the proportions of nitrogen and oxygen, so it is a minor component.
Key terms
- Atmosphere
- The layer of gases around Earth.
- Mixture
- Two or more substances present together without forming one pure substance.
- Major component
- A substance present in a large proportion of a mixture.
- Minor component
- A substance present in a small proportion of a mixture.
- Dry air
- Air described without including its water vapour.
- Percentage by volume
- A percentage that describes a gas’s share of the volume of a gas mixture.
Continue through SCH3U
View the complete SCH3U Ontario Grade 11 Chemistry curriculum and lessons
- F1.1 · Analyse air-quality impacts and propose carbon-footprint reductions
- F1.2 · Assess air quality and Canadian pollution-reduction initiatives
- F2.1 · Use gas-law and atmospheric-chemistry terminology
- F2.2 · Investigate pressure, volume, and temperature relationships
- F2.3 · Solve problems with major gas laws and the ideal gas law
- F2.4 · Solve stoichiometry problems involving gases
About this lesson and its review
Published by DoAssignment. This AI-assisted lesson follows Ontario Grade 11 Chemistry (SCH3U), expectation F3.1. It is a study resource, not an official curriculum publication.
Before publication, the draft is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability, and then requires administrator approval. Errors can still occur, so corrections are welcomed.