ELECTRON THEORY

Transcription

1 ELECTRON THEORY

2 We will start our discussion of electron theory with a few definitions. Matter- is anything that has mass and takes up space. The basic unit of matter is the atom.

3 Another Definition Energy- is the ability to do work. There are two forms of Energy. 1. Heat Energy 2. Light Energy When we apply heat or light to an object we are able to make it work for us.

4 As I said, the basic unit of matter is the Atom. The Atom is made up of: The Nucleus- which is made up of protons and neutrons Electrons- which revolve around the nucleus in paths called orbits or shells.

5 The Atom

6 A substance that is made of atoms that are all the same, is called an Element. A substance that is made up of two or more different elements is called a Compound. A substance that is the smallest particle of a compound and still contains all the characteristics of that compound is called a Molecule.

7 Electric Charges Neutronshave a negative charge. Electrons- Protons- have a positive charge. have a no charge. An Electrically Neutral atom has the same number of Protons and Electrons.

8 The number of Protons plus the number of Neutrons is the Atomic Weight. The number of Protons is the Atomic Number.

9 The negatively charged ELECTRONS are held in their orbits by their attraction to the positively charged PROTONS.

10 Electrons in the outermost shell are called Valence Electrons. Valence Electrons that leave the outermost shell are called Free Electrons.

11 When an atom loses electrons it becomes a positively charged Ion. When an atom gains electrons it becomes a negatively charged Ion. The process by which atoms gain or lose electrons is called Ionization.

12 Some materials hold their electrons very tightly. Electrons do not move through them very well. These things are called Insulators. Plastic, cloth, glass and dry air are good insulators. Other materials have some loosely held electrons, which move through them very easily. These are called Conductors. Most metals are good conductors. Like aluminum, gold, silver and copper.

13 The simplest form of electricity is called Static Electricity.

14 Cause of Static Electricity Static electricity is usually caused when certain materials are rubbed against each other, like wool on plastic or the soles of your shoes on the carpet. The process causes electrons to be pulled from the surface of one material and relocated on the surface of the other material.

15 Rubbing a balloon on a wool sweater creates charges on the surfaces. The material that loses electrons ends up with an excess of positive (+) charges. The material that gains electrons ends up an excess of negative (-) charges on its surface.

16 Charges on Surface Note that the charged atoms are on the surface of the material. Static electricity is different than regular electricity that flows through metal wires. Most of the time the materials involved in static electricity are nonconductors of electricity. If electrical charges build up on the outside of a metal, most of them will dissipate into the metal, similar to an electrical current.

17 Rub a balloon on a wool sweater. The balloon collects negative electrical charges on its surface and the wool collects positive charges. You can then stick the balloon to the wall, which does not have an excess of either charge. The balloon will also stick to the wool, although the charges may jump back to the original material in a short time.

18 You can also run a comb through your hair to charge the comb with static electricity. The comb can then be used to attract neutral pieces of tissue.

19 How a Battery Works

20 A basic law of the universe is that like charges repel and unlike attract. Two negatives will repel each other. A negative and a positive will attract each other. An electron has a negative charge. The negative terminal of a battery will push negative electrons along a wire. The positive terminal of a battery will attract negative electrons along a wire. Electric current will therefore flow from the negative terminal of a battery, through the lamp, to the positive terminal.