AP Chemistry
Bonding Tetrahedron Project and Armor Reading
Please visit these URLs: (Note that the SDUHSD policy on non-SDUHSD links applies here.)
http://www.meta-synthesis.com/webbook/38_binary/binary.php?mge_1=Al&mge_2=B
http://www.meta-synthesis.com/webbook/38_laing/tetrahedra.html#TT
http://www.meta-synthesis.com/webbook/37_ak/triangles.html
Be sure and play around with the synthlet at the top of the first link.
Go ahead and construct the tetrahedron if you would like:
http://www.meta-synthesis.com/TT.pdf
1. Use the tetrahedron, the synthlet, or other resources to categorize the following compounds as either metallic, ionic, covalent, or network covalent: AlCl3, TiC, SiF4, SiH4, SiC, SF4, H2S, CO2, CuZn, CuSn, PbCl2, PbC, AsI3, AsF3, SbCl3, SbF3, SF6, O2, graphite, diamond, carbon nanotubes, gallium arsenide, gallium nitride, CH4, steel, duralumin, cupronickel, brass, NaI, FeCl2, chromyl chloride, CrO2Cl2, nylon.
2. List the properties of materials that have each type of bonding.
Read the reading below on armor. Answer the questions.
Armor has evolved from animal skins to synthetic materials. Its purpose is to protect a person or object. It’s obvious that steel makes good armor, but what about glass, plastic, and water? Read further to find out.
The earliest types of armor were made from natural materials such as skins, wood, and bone. They would have been designed to stop weapons made from wood, bone, and stone. As metal weapons were deployed most of the early types of armor would have been obsolete. In response new materials were employed. These included leather and metals.
In the age of sail ships used their wooden construction, often up to three feet thick, as a form of armor. As projectiles became more powerful this proved inadequate. Iron was used as an armor material but proved ineffective as it is too soft. Cast iron, an alloy of ion and carbon, was too brittle. When steel became easier to produce in thick plates it was adopted. The problem with battleship armor was making steel that was hard enough to shatter a projectile but ductile enough to absorb the impact without itself shattering. There is no type of steel capable of this so a technique called face hardening was developed. This allowed the front of the armor to be hard but brittle and the back to be soft but ductile. Some armors had an additional very thin very hard layer at the front. The steel that was hardened in this way was called carburized. Carbon was added to the steel which was then heat treated to make it extremely hard. Unfortunately it was also very brittle.
Today armor is mostly found protecting personnel and land vehicles. Personnel wear body armor that can consist of steel and titanium sheets, ceramic plates, and tough cloth made from polymer. Various forms of armor protect vehicles but perhaps the most interesting armor is found on tanks. Tanks cannot use a thickness of metal to protect them from attack. Tanks must endure attack from kinetic energy projectiles that consist of a dart made from tungsten or uranium metal. These darts can travel over 1.5 kilometers per second. They also suffer from chemical energy projectiles. These devices use explosives to turn a metal cone inside out in milliseconds, generating a metal plasma jet that can penetrate over a meter of steel. A cubic meter of steel weighs over 7 tons. This would be enough steel to cover 1 square meter of the tank to a thickness of 1 meter, a thickness that is inadequate despite the enormous weight of the armor. Instead of thick steel, tanks use a combination of materials for protection. These include:
Steel
Titanium
Aluminum
Fiberglass
Plastic
Ceramic
Tungsten
Uranium
Air
Each of the above materials has advantages and disadvantages. Tungsten is very hard and tough but also heavy. Plastic is light but not hard or tough enough. Aluminum is lighter than steel but not as tough. Titanium is harder than steel or aluminum, tougher than both and lighter than steel. It is about 50% heavier than aluminum and it is expensive. Uranium hard and dense but it is also toxic and if a vehicle protected by it is defeated uranium dust can affect the crew. Ceramic is harder than metal but much more brittle. A combination of the above materials is used for armor. For example, a vehicle might use armor that has a tungsten plate to break projectiles backed by ceramic to stop chemical energy. This could be followed by plastic or aluminum to give a lightweight but tough added layer. Air layers are used to disperse the plasma jet of chemical energy projectiles. Air is light and cheap but has no effect against kinetic energy projectiles.
Armor is defeated either by shattering or by plastic deformation where it moves out of the way of the projectile. Ideally armor would be too hard for deformation and too ductile too shatter. There are no materials in existence that fit this description.
This suit of armor consists of steel plates.
This suit relies upon steel as well but is more flexible and has materials like lacquer as well. The lacquer protects the steel from rusting but also gets in the way of projectiles.
Questions:
1. Calculate how much more mass a 50mm thick 1m square tungsten plate has compared to a 50mm thick 1m square steel plate.
2. The gas ethyne is used in the carburization process because it is carbon rich. Calculate the mass percent of carbon in ethyne. Ethyne is also known as acetylene and its formula is C2H2.
3. A material proposed for armor is TiB2. What is the nature of the bonding in this material?
4. Glass can be a suitable armor material if used properly. Glass has the formula SiO2. Above silicon in the periodic table is carbon. CO2 is a gas at room temperature but glass is a solid. Explain why.
5. Explain why metals are ductile.
6. Explain why the addition of carbon to steel makes it harder.
7. One of the jobs available for engineers and scientists is working for the CIA analyzing foreign technology. A scientist analyzes a sample of armor and finds these materials: A. A ductile, malleable conductive plate B. A hard, brittle, insulating plate C. A soft, pliable plate that is flammable What type of bonding is exhibited by the armors?
Answers:
First set:
AlCl3 Polar covalent
TiC Metallic but kind of network covalent
SiF4 Molecular covalent
SiH4 Molecular covalent
SiC Network covalent
SF4 Molecular covalent
H2S Molecular covalent
CO2 Molecular covalent
CuZn Metallic
CuSn Metallic
PbCl2 Ionic
PbC Your guess is as good as mine, honestly, I’m not sure this compound exists. I put SnC into the synthlet and got network covalent but close to ionic and metallic.
AsI3 Molecular covalent
AsF3 Molecular covalent
SbCl3 Molecular covalent
SbF3 Molecular covalent
SF6 Molecular covalent
O2 Molecular covalent
Graphite Metallic
Diamond Metallic
carbon nanotubes Metallic
gallium arsenide
gallium nitride,
CH4 Molecular covalent
Steel Metallic
Duralumin Metallic
Cupronickel Metallic
Brass Metallic
NaI Ionic
FeCl2 Ionic
Chromyl chloride CrO2Cl2 Molecular covalent but a somewhat ionic
Nylon Molecular covalent
2. Ionic compounds are hard, brittle electrolytes. They are insulators when solid. Many have high melting points. Molecular covalent compounds are insulators. Their melting points vary but typically are low. Covalent network compounds are insulators with high melting points. Some are soft, some are hard. Metals are conductors with variable but relatively high (for most) melting points.
Second set:
1. Find the volume of the plates. I got 50,000 ml for both plates. The steel plate will be modeled as iron (density around 7.9g/ml). The tungsten plate has density about equal to 19.3g/ml. The mass of the steel plate is 395 kg while the tungsten plate has a mass of 965 kg. The difference is 570kg.
2. 92.3% carbon by mass.
3. Wow. I didn’t know hard this would be when I made the problem. I looked at the page on wiki and I saw that the melting point is up with the covalent network solids. The synthlet doesn’t have Ti so I put in Al since the electronegativity of Ti is 1.54 and Al is 1.61. It told me that TiB2 is semi-metallic. I decided I don’t trust the synthlet now because the synthlet uses electronegativity which I do not believe is worth much as a concept. The electrical conductivity of TiB2 is higher than that of semiconductors. The structure of titanium diboride from wiki looks like any crystal which doesn’t help much:
I also read on wiki that TiB2 has good wettability with Al which suggests metallic character. Wettability is the degree to which a liquid will interact with a solid. Think about paper towels. Paper towels absorb water well whereas plastic wrap does not. Paper towels have better wettability than plastic wrap. I am going to go ahead and agree that the compound is kind of metallic but the electrons aren’t that mobile which I guess you could say that makes it semi-metallic. Personally, I would think of TiB2 as similar to steel (which is metallic but stronger than TiB2) with the Ti acting like Fe and the B acting like C if I were working with TiB2. I would think about it this way until that made me make a mistake and then I’d come up with a new way to think about it.
4. The synthlet lies to dedicated chemists like us because of its simplistic reliance upon electronegativity. In real life carbon dioxide molecules attract each other with dispersion forces while glass is network covalent. CO2 is molecular covalent. SiO2 is network covalent.
5. Metals are ductile and malleable because as they move the electrons can continue to be shared. That is, the bonding doesn’t get disrupted (much) by the change in the metal’s shape. Conversely, if an ionic solid moves the interaction between + and – would be disrupted. Same with network covalent since the orbitals need to interact in order for there to be bonding. If we move the atoms in space relative to each other then they might not interact as well or at all. Think about bond angles. We have from 180 down through 60 but most are 100-125. That’s a 25 degree range and really the bonding is considerably strained upon moving a few degrees.
6. The carbon atoms fit into holes in the crystal structure of the iron and bond with the iron increasing the forces holding the whole thing together.
7. Metallic, network covalent (probably a ceramic plate), and molecular covalent (this is probably Kevlar or nylon plate).