A Simple Model of the Structure of matter
Basic concepts
- All matter is composed of atoms
- Electric charges are carried by electrons and protons
- Protons are found in a small central region of atoms called the nucleus.
- Electrons move about the space surrounding the nucleus. They carry a negative electric charge equal in magnitude to that on the proton.
- Neutrons have no charge and are found in the nucleus.
- Atoms gaining electrons have a net negative charge and are called negative ions.
- Atoms losing electrons have a net positive charge and are called positive ions
- Atoms are normally electrically neutral. That is, the number of protons = the number of electrons.
- Elementary charge – The charge on a proton or electron.
- The electron has a mass of 1/1836 th the mass of the proton.
Consider Solids
- Atoms are held tightly in place and can’t move about to escape.
- Charging a solid means adding or removing electrons from it.
- All electric charges in solids result from either an excess or deficit of electrons
- Solids are either:
- Conductors – A material in which charges are able to move easily from one atom to the next.
- Insulators – A material in which charges are not free to move easily about from atom to atom.
- Free electrons – electrons in solid conductors, that can move easily about.
Consider Liquids
- Molecules are free to move about in liquids.
- If the molecules of the liquid are neutral, then the liquid will not conduct
- If the atoms are charged (ions) then the liquid will conduct.
- Water is an e.g. of an insulator.
- Salt water is an e.g. of a conductor because the salt breaks up into Na+ and Cl- ions.
Consider Gases
- Molecules again are mobile.
- most gases are neutral and therefore are insulators.
- If exposed to radiation, (e.g. x-rays) the molecules may ionize and therefore conduct electricity.
- Humid air can conduct electricity because water molecules are able to partially separate into positive and negative ions.
- Humid air may also contain dissolved materials that ionize.
December 6, 2013