domingo, 21 de marzo de 2010

Metal Information: What is a Metal?

Our common experience of metals is that they are shiny, hard and conduct electricity. In order to understand how this makes metals useful in batteries, we need to know about the structure of metals and how this gives them the properties we are familiar with. This discussion is restricted to pure metals such as lead, gold, copper and so on; alloys will be addressed elsewhere.
Metal Information: Definition of a Metal
copper metal
A metal is defined as any element that loses its outer shell electrons to become stable. Since neutral atoms have equal numbers of electrons (- charge) and protons (+ charge). Therefore when a metal atom loses electrons it becomes positively charged. This charged particle is called an ion
This is the state virtually all metal atoms are in when encountered in the real world. These positive ions are almost always combined with non-metal negative ions like chloride and fluoride to make ionic compounds. These are everywhere; Sodium Chloride is sodium metal and chloride non metal. Rust is some combination of Iron metal and oxide non metal, such as Fe2O3. Virtually everything that is not organic is an ionic compound.
Metal Information: How Are Pure Metals Made?
There are various techniques for separating the metal ions from the non-metal ions in a substance. Whether by heating or dissolving in a solution and using an electric current to isolate them, the effect is the same - to isolate the positive metal ions. These processes also involve the supply of electricity.
When the positive metal ions encounter free electrons, and there is nothing nearby to remove the electrons, they reform into complete metal atoms. These metal atoms adhere to each other and so metal crystals grow. Once in a metal crystal, a metal atom still has a very weak hold of its outer shell, or valence, electrons. These electrons tend to drop off and float around the now once more positively charged metal ion. These are called delocalised electrons.
The result of many millions of atoms doing this is that there are layers of positive ions surrounded by a "sea" of delocalised electrons. The negative charges of the electrons hold the positive ions in place, and vice versa.
Metal Information: The Properties of Metals This model for the structure of metals explains the properties we are familiar with.
Conductivity The free electrons can move, and so when electrons are pushed in at one end of a piece of metal others come out at the other end. There are no empty spaces in the metal. The easiest way to visualise this is as a hose filled with marbles; when one goes in another comes out immediately at the other end. Thus current can flow through metals. It is this presence of available electrons in metals that enable them to be used to generate current in batteries.
Lustre The lustre, or shine, of metals is caused by the electrons reflecting light. All pure metals reflect well. Metals that do not seem to do so, like lead, are coated with a thin layer of oxide (rust). If this layer is scraped off, the reflective metal can be seen underneath.
Strength The pull between the layers of positive ions and negative electrons is very strong and holds the layers tightly together. This is not immediately obvious from this model of bonding.
Being Prone to Corrosion The free electrons can be absorbed by other substances, such as oxygen gas in the atmosphere. When this happens there is an imbalance of electrons and positive ions in the metal, and the unbalanced metal ions will form ionic bonds with other chemicals, and rust is produced.

Hernandez Caballero Indiana M. CI: 15.242.745
Asignacion: EES

No hay comentarios:

Publicar un comentario