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Atoms & molecules

3 minute Presentation of chapter 2 section 2.

jonathan tiwari

on 5 May 2010

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Transcript of Atoms & molecules

Atoms What is a Atom? What is it made of? What does it look like? Atoms are the basic building blocks of matter Atoms are made of particles called protons, electrons and neutrons. There are many atoms but heres a
look at a helium atom. Molecules What is a molecule? the smallest physical unit of an element or compound, consisting of one or more like atoms in an element and two or more different atoms in a compound.
(Water molecule) What is it made of? Atoms What to molecules look like? Molecules all look different but in turn have basic structure
(DNA) Atoms and molecules are always in motion All molecules are in constant motion. Molecules of a liquid have more freedom to movement than those in a solid. Molecules in a gas have themost freedom to motion.
Heat, temperature and the motion of molecules are all related. Temperature is a measure of the average kinetic energy of the molecules in a material. Heat is the energy transferred between materials that have different temperatures. Increasing the temperature increases the movement of motion of molecules. Energy is related to temperature by the relationship. And the same for atoms.
Presentation 1 of 3
Kinetic theory is a scientific theory regarding the nature of gasses. The theory goes by many names, including the kinetic theory of gasses, kinetic-molecular theory, collision theory, and the kinetic-molecular theory of gases. It explains the observable and measurable, also called macroscopic, properties of gasses in terms of their molecular composition and activity. While Isaac Newton theorized that the pressure of a gas is due to static repulsion between molecules, the kinetic theory holds that pressure is the result of collisions between molecules.
The kinetic theory makes a number of assumptions about gasses. First, a gas is made of very small particles, each with non-zero mass, constantly moving in a random manner. The number of molecules in a gas sample must be large enough for statistical comparison.

Kinetic theory assumes that gas molecules are perfectly spherical and elastic, and that their collisions with the walls of their container are also elastic, meaning that they do not result in any change in velocity. The total volume of gas molecules is negligible as compared to the total volume of their container, meaning that there is ample space between the molecules. In addition, the time during the collision of a gas molecule with the container wall is negligible in relationship to the time between collisions with other molecules. The theory further relies on the assumption that any relativistic or quantum-mechanical effects are negligible, and that any effects of the gas particles on each other are negligible, with the exception of the force exerted by collisions. Temperature is the only factor affecting the average kinetic energy, or energy due to motion, of the gas particles.

These assumptions must be maintained in order for the equations of kinetic theory to function. A gas fulfilling all of these assumptions is a simplified theoretical entity known as an ideal gas. Real gases usually behave similarly enough to ideal gases for kinetic equations to be useful, but the model is not perfectly accurate.

Kinetic theory defines pressure as the force exerted by gas molecules as they collide with the container wall. Pressure is calculated as the force per area, or P = F/A. Force is the product of the number of gas molecules, N, the mass of each molecule, m, and the square of their average velocity, v2rms, all divided by three times the length of the container, 3l. Therefore, we have the following equation for force: F = Nmv2rms/3l. The abbreviation, rms, stands for root-mean-square, an average of the velocity of all the particles.

The equation for pressure is P = Nmv2rms/3Al. Since area multiplied by length is equal to volume, V, this equation can be simplified as P = Nmv2rms/3V. The product of pressure and volume, PV, is equal to two-thirds the total kinetic energy, or K, allowing the derivation of macroscopic properties from a microscopic one.

An important part of the kinetic theory is that kinetic energy varies in direct proportion to the absolute temperature of a gas. Kinetic energy is equal to the product of the absolute temperature, T, and the Boltzman constant, kB, multiplied by 3/2; K = 3TkB/2. Therefore, whenever temperature is increased, kinetic energy is increased, and no other factors have an effect on kinetic energy
(Note: THis is all from the hhtp url. http://www.wisegeek.com/what-is-kinetic-theory.htm) Kinectic Theory
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