Atomic Theory

“All things are made up of atoms.”

States of matter

Solid, liquid, gas, and plasma

State of Solids

  • Has definite shape and volume
  • High density and not very compressible
  • Does not depend on the shape of the container (doesn’t fill it in)

State of Liquids

  • Has a fixed volume
  • Takes the shape of container
  • Less dense than solids
  • Almost incompressible

State of Gases

  • Takes the shape of the container
  • Takes the volume of container (this means that the gas molecules can be spread out evenly in the container or compressed in a smaller container. The volume is when the molecules are evenly distributed.)
  • Can be compressed
  • Gases are in the gaseous state at room temperature
  • Gases have more energy than liquids, and solids.
  • Gases are less dense.

State of Plasma

Plasma is simply an ionized gas, where the gas is charged with free electrons and positive ions because of the amount of energy plasma contains.

Unit 2.1 – Gases and the Atmosphere


Our atmosphere –

Our atmosphere is composed of various elements such as nitrogen, oxygen, argon, neon and carbon dioxide. Although we need oxygen to survive, oxygen is not the most abundant gas in our atmosphere. The inert nitrogen gas actually makes up the highest composition with a percentage of about 78% while oxygen makes up 21% with argon and neon making up 0.9% and 0.002% respectively.  With the amount of press of the increased amount of carbon dioxide in the atmosphere, carbon dioxide makes up only 0.035% of the earth’s atmosphere. Although, CO2 has only 0.035% in our atmosphere, its impact is significant.

Weight of our atmosphere

1644 – “We live submerged at the bottom of an ocean of the element air, which by unquestioned experiments is known to have weight.” Torricelli

Although we cannot see the air molecules, air molecules in our atmosphere play a pivotal role in many day to day activities. As we learned in our last unit, boiling point is directly related to the about of molecules in our atmosphere called atmospheric pressure, the amount of dissolved gas molecules in our oceans depend on pressure, air allows our air planes to glide over, helicopters to levitate by the air molecules, protects us from harmful radiation, warms the earth and creates ocean currents for weather patterns.

The diagram below depicts how the air molecules behave. From our previous section, remember that gas molecules behave by moving in a straight line with random motion. They exert pressure based on their movement.  The air molecules gravitate around the earth’s surface, thus, there are more molecules near the earth’s surface than higher up in the atmosphere.


The change of composition of the atmosphere

Composition of the atmosphere has changed since how the earth began. It is believed that billions of years ago, the atmosphere consisted mainly of ammonia, methane and water vapour. It is hypothesized that blue-green algae were the first primitive organisms to convert CO2 to O2 via photosynthesis to give rise to the amount of oxygen in our atmosphere. Free oxygen was not present in the primitive earth and it wasn’t until 1 Billion years ago when blue-green algae performed photosynthesis to convert the CO2 into O2. More descriptive writeup can be found here

Greenhouse gases

Greenhouse gases are elemental gas molecules that contribute to the warming of the earth. Carbon dioxide, CFC, methane and others play a vital role in the warming of the earth by trapping the sun’s energy.