All matter is made up of particles (particle model). Since particles are constantly moving (kinetic theory), we should be able to explain all the properties of matter in terms of particle motion.
On this page, we will consider states of matter, forces and Brownian motion in relation to the particle model.
Key Concepts
Greek philosophers thought that it must be impossible to keep cutting a piece of matter in half. Therefore, a material was assumed to be made up of smaller amounts of that same material. When a piece of material became so small that it was indivisible, it was called "atomos".
This would have meant that cheese was made of 'cheese atoms' and clay was made of 'clay atoms'.
The properties of solids, liquids and gases can be explained using the particle model.
This can't act as a proof of kinetic theory, but it is a form of supporting evidence.
The forces of friction, drag and buoyancy can be explained using the particle model.
Brownian motion is the zig-zag motion of smoke particles viewed under a microscope, or of pollen on the surface of water, or perfume in air. This led to the proposal that surrounding invisible particles existed to knock the smoke particles about, thus refuting the Greek theory.
This provides considerable evidence for the particle model.
Avogadro worked out that the number of particles in equal volumes of different gases at the same pressure and temperature must be the same.
Take a moment to consider the signficance of this statement. In the room where you are sitting, regardless of whether it contained air, pure oxygen, argon or chlorine, it would contain exactly the same number of particles. (Your lungs might notice though...)
This led to Avogadro's constant, defined on the Thermal concepts page.
\(N_A\) = 6.03 x 1023
When this number of particles are grouped together, the collective term is the mole (n). So, to calculate the number of moles present in a sample, divide the number of particles by Avogadro's constant:
\(n={N\over N_A}\)
Elements in the Periodic Table are displayed with a symbol (an uppercase letter, usually followed by a lowercase letter) and two numbers. The smaller atomic number represents the number of protons in the nucleus. The larger relative atomic mass number represents the sum of the protons and neutrons in the nucleus.
Different elements have different numbers of protons and so are given different squares on the Periodic Table. The relative atomic mass can vary for a given element if different numbers of neutrons are present; these are called isotopes of the same element.
The relative atomic mass displayed is the average for a given element (hence why some are not whole numbers). Since hydrogren atoms contain just one proton, and because protons and neutons have approximately the same mass, each element's mass is a multiple of the mass of a hydrogen atom.
How much of Particle model (kinetic theory) have you understood?
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