iGCSE Chemistry (Triple) CAIE

This subject is broken down into 70 topics in 12 modules:

  1. Chemistry of the Environment 10 topics
  2. The Particulate Nature of Matter and Experimental Techniques 4 topics
  3. Atoms, Elements and Compounds 6 topics
  4. Stoichiometry, Electricity and Chemistry and Chemical Energetics 5 topics
  5. Chemical Reactions 4 topics
  6. Acids, Bases and Salts 4 topics
  7. The Periodic Table 5 topics
  8. Metals 4 topics
  9. Air and Water 3 topics
  10. Sulfur and Carbonates 2 topics
  11. Organic Chemistry 8 topics
  12. Principles of Chemistry 15 topics
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This page was last modified on 9 January 2025.

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Chemistry (Triple)

Chemistry of the Environment

Composition of Air

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Composition of Air

Composition of Air

Dry, unpolluted air is a mixture of gases and small amounts of water vapour. The major gases that make up the air are:

  • Nitrogen (N2): This is the gas that makes up most of the air. Approximately 78% of air (by volume) is nitrogen.

  • Oxygen (O2): The gas necessary for most life forms. Approximately 21% of the air is oxygen.

  • Argon (Ar): This is a noble gas. It makes up 0.9% of the air.

  • Carbon dioxide (CO2): Though present in relatively small amounts (0.04% of the air), this is a crucial gas because it helps to control the Earth's temperature.

  • Other gases: These include helium (He), methane (CH4), neon (Ne), krypton (Kr) and xenon (Xe), which collectively make up less than 0.1% of air.

Properties of Major Gases in Air

Air is a mixture, and each gas in the air retains its property. These include:

  • Nitrogen: An inert gas and it does not readily react with other substances. It is colourless, odourless and tasteless.

  • Oxygen: A reactive gas which reacts with many substances. It is also colourless, odourless and tasteless.

  • Argon: A noble gas and hence, very unreactive. It too is colourless, odourless, and tasteless.

  • Carbon Dioxide: Although not a noble gas, it is fairly unreactive under normal conditions. It is also colourless, odourless, but not tasteless - it gives fizzy drinks their "fizz".

Role in the Environment

  • Nitrogen: It's an essential nutrient for plants and animals. It's converted into nitrates by bacteria, which plants can use. Animals then eat the plants for protein.

  • Oxygen: Necessary for respiration in most organisms. It is also needed for combustion (burning).

  • Carbon dioxide: Absorbed by plants for photosynthesis. Also acts as a greenhouse gas, trapping some of the heat from the Sun, and thereby warming the planet.

  • Argon and other noble gases: These are mostly unreactive and do not contribute significantly to chemical reactions in the atmosphere.

Measuring Air Composition

The composition of air can be measured using various methods. But a simple method involves separating the components of air through fractional distillation. In this process, air is first cooled to a very low temperature (-200°C) until it liquefies. It's then slowly heated, and different components boil off at different temperatures, allowing them to be collected separately. Nitrogen boils off first, followed by argon, and then oxygen. The remaining gases, like CO2 and noble gases, can also be collected.

Course material for Chemistry (Triple), module Chemistry of the Environment, topic Composition of Air

Chemistry (Triple)

The Periodic Table

The Periodic Table: Group Properties

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The Periodic Table: Group Properties

Group Properties: Alkali Metals (Group 1)

  • The Alkali Metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).
  • They are characterised by having one electron in their outermost shell, making them very reactive.
  • As you go down the group, the reactivity increases. This is due to the outermost electron being further from the nucleus, making it easier to lose and thereby increasing reactivity.
  • Alkali Metals react vigorously with water to produce alkaline solutions and hydrogen gas.
  • They all have low densities and melting points compared to most other metals.

Group Properties: Alkaline Earth Metals (Group 2)

  • The Alkaline Earth Metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra).
  • They have two electrons in their outermost shell, which contributes to their chemical properties.
  • Reactivity increases down the group, similar to Group 1, due to the outer electrons being further away from the nucleus.
  • Alkaline Earth Metals also react with water to produce alkaline solutions, but do so less vigorously than Alkali Metals.

Group Properties: Halogens (Group 7)

  • The Halogens include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
  • They all have seven electrons in their outermost shell, making them highly reactive, as they need just one more electron to achieve a full outer shell.
  • Unlike Groups 1 and 2, reactivity decreases down the group. This is because the atoms are larger and the outermost electrons are further from the nucleus, making it harder to gain an additional electron.
  • Halogens exist as diatomic molecules (two atoms) in their elemental state.
  • They have varying physical states at room temperature: fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid.

Group Properties: Noble Gases (Group 0 or 8)

  • The Noble Gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn).
  • They all have a full outer shell of electrons, making them extremely stable and unreactive.
  • The boiling and melting points of the Noble Gases increase down the group due to an increase in van der Waals forces as the size of the atoms increase.
  • They are all colourless gases at room temperature and are commonly used in lighting and lasers due to their ability to emit light when electricity is passed through them.

Course material for Chemistry (Triple), module The Periodic Table, topic The Periodic Table: Group Properties

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