Week 8 Assignment - Balancing Acts

1. Semi-conductor of the Week
2. Chembalancer!
3. gEN-chEM - Balancing equations

1.
Semi-conductors: substances that conduct a limited and controllable amount of electricity. They can be made from single substances or a combination of materials. It's all about the electrons and the interplay of harmonious and disharmonious exchanges of these pieces of energy:

In a semiconductor, the distance between the valence band and the conduction band is fairly small. At a low temperature the semiconductor has a completely filled valence band. There are no empty energy positions available for the electrons to be accelerated in. Therefore, at low temperatures the semiconductor behaves like an insulator. At room temperature, the atoms in the semiconductor material vibrate enough so that a few electrons may escape from their positions in the valence band into unoccupied positions in the conduction band. The conduction at room temperature, however, is so small that no significant current can be said to pass. (1)

Arsenic - 33

atomic mass - 74.92

Three metalloidal forms of arsenic with different crystal structures are found free in nature (the minerals arsenic sensu stricto and the much rarer arsenolamprite and pararsenolamprite), but it is more commonly found as arsenide and arsenate compounds. Several hundred such mineral species are known. Arsenic and its compounds are used as pesticides, herbicides, insecticides and various alloys.

Elemental arsenic is found in many solid forms: the yellow form is soft, waxy and unstable, and is made of tetrahedral As₄ molecules similar to the molecules of white phosphorus. The gray, black or 'metallic' forms have somewhat layered crystal structures with bonds extending throughout the crystal. They are brittle semiconductors with a metallic luster.

Gallium arsenide is an important semiconductor material, used in integrated circuits. Circuits made using the compound are much faster (but also much more expensive) than those made in silicon. Unlike silicon it is direct bandgap, and so can be used in laser diodes and LEDs to directly convert electricity into light. (2)

And by the way, I prefer to learn about semi-conductors from Britney Spears (acutally, this is not a very helpful site). If you really want a great lesson in semi-conductors, I reccomend this site: Nobel Prize.org - Semi-Conductors

2.
ChemBalancer - This is a slightly under-developed yet useful quiz that is helpful in refreshing the basic arithmetic skills needed to do chemical equation balancing. I find it useful but slightly confusing in it's design.

I scored well after it figured out what it wanted me to enter into the boxes.

3.
General Chemistry - Balancing Equations Tutorial -
I had to open Internet Explorer and download some plug-ins in order to do this exercise. This is not ideal and in fact, quite annoying. In any case, once it got going, it was quite fun and visually well-designed and easy to follow.

I think this is a very useful educational tool.