Carbon vs.Silicon

An Inquiry bySarah Campeau and

Lindsey Schinkel

The PurposeTo prove that the elements: carbon and silicon are composed of different atoms.

We will prove this in three main ways. By comparing the physical properties, chemical properties, and atomic components of carbon to those of silicon.

Atomic Components• The atoms of carbon and silicon are made up of different amounts

of protons, neutrons and electrons and therefore have different atomic masses.

• Based on their position in the periodic table we see a different in their categories. Carbon is a non-metal, and silicon is a metalloid.

Physical Attributes• Colour: The colour of silicon is a shade of grey while carbon is black.• Density: The density of silicon is 2.33g/cm³ and that of carbon is 2.62g/cm³.• Hardness: Carbon can vary in it’s hardness, from graphite at 0.5 mohs to

diamonds at 10.0 mohs. Silicon has a hardness of 7.0 mohs.(The carbon we used was charcoal, which is similar to graphite, so we noticed the difference in the two element’s solidity.)

• Luster: Being similar to a metal, silicon has a touch of luster to it. Carbon does not have any luster in the charcoal form.

Physical Attributes (cont’d)• The melting point of silicon is 1414˚C and it’s boiling point is 3265˚C. The melting

point of carbon is 3550˚C and it’s boiling point is 4027˚C. However, unless carbon is under extreme pressure, when heated will undergo sublimation.

• Abundance in the earth’s crust: The earth’s crust is composed 27% of silicon and only 0.18% carbon.

• Conductivity:Carbon: Electrical- 0.00061 106/cm

Thermal- 1.29 W/cmKSilicon: Electrical- 2.52E-12 106/cm

Thermal- 1.48 W/cmK

• Crystal Form:Silicon’s crystal form is a diamond-cubic shape. Carbon depending on whether it is in it’s diamond form, which has a cubic crystal form, or it’s graphite form, which has a hexagonal crystal form, can be very different.

Chemical Properties

• Reaction with air: Silicon has no reaction to air, whereas carbon reacts vigorously forming CO₂.

• Reaction with Sodium Hydroxide (Base): Silicon reacts mildly with NaOH forming silicates. Carbon has no reaction with this base.

• Alloys: Silicon is used in many alloys such as copper, iron and aluminum alloys, to enhance certain aspects of the metal. Carbon is mostly alloyed with iron to form carbon steel.

Procedure 1Comparing Density

Hypothesis: The densities should be different because the number of subatomic particles varies, resulting in different masses and consequently different densities.

Procedure: 1. Measure 30mL of water in the 100mL graduated cylinder. Pour the water into the

100mL beaker.2. Place the empty weigh boat on the mass balance and press the tear button. Place

the carbon in the weigh boat. Take note of the mass.3. Carefully place the piece of carbon into the beaker of water. Take note of the

amount of water the carbon displaces, that is to say the new volume. Subtract the new volume from the first volume of 30mL to get the volume of the piece of carbon.

4. Calculate the density by dividing the mass by the volume.5. Repeat steps 1-4 for the piece of silicon.

Results and Elaborations• Our results of the density procedure was, we believe, in correct. We found the density of carbon to be 0.31

g/cm³ and that of silicon to be 0.76g/cm³. The actual densities are 2.26g/cm³ and 2.33g/cm³ respectively. We were not entirely sure where we made our error.

• It is possible the reason our densities were inaccurate was related to the fact that the carbon floated and was thus not completely submerged in the water.

• We questioned whether the size of the pieces of carbon and silicon influenced the calculation of density that we gathered.

• Though the densities we found were not congruent with the real densities, they were different from each other.

Note:• We measured the mass of the carbon and silicon first incase they absorbed some of the water when we

calculated the volume, and that would have given us inaccurate results.

Procedure 2Comparing

Conductivity

Hypothesis: Since Carbon and Silicon are elements with different classifications (because theyhave different atoms) they will have different levels of conductivity.

Procedure:1. Attach the ends of two wires to the two sides of the ohmmeter by wrapping the ends around the

terminals.2. Attach by twisting the end of one of those wires to the terminals on the battery. Attach by twisting

one end of the third wire to the other battery terminal.3. Touch the two loose ends of wire (one connected directly to the battery, the other to the ohmmeter)

to either end of the piece of carbon by having an experimenter hold the insulated part of the wire.4. Turn on the ohmmeter and take note of the amount of resistance on the screen on the ohmmeter.5. Turn off the ohmmeter.6. Remove the carbon form the circuit. Place the piece of silicon where the carbon was, so both ends

are touching a wire being held at the insulated spot by an experimenter. 7. Turn on the Ohmmeter. Take note of the amount of resistance the screen displays.

Results and Elaborations• We found that carbon was very conductive, the Ohmmeter read 1.54 volts with just the battery

in the circuit, and when the carbon was added in, the voltage changed by just 0.01 volt to 1.53 volts.

• We were a little disappointed when we could not get the conductivity of silicon because the Ohmmeter was giving us many reading, changing to numbers anywhere between 0.15 and 1.09 volts.

• Though we did not find the conductivity to compare, we did find out that carbon in charcoal form can be molded nicely into a shape, such as a cylinder. While silicon however comes off in an irregular form and is too hard to shape into a regular shape.

• To do this over again, we would probably not do it since it is important to have a regular shape for the current to flow through, and that’s not easy with silicon.

Procedure 3Testing reaction

to HCl

Hypothesis: The reaction of silicon and carbon should be different because silicon is part of the metalloids which means it should react differently then a non-metal like carbon.

Procedure:1. Measure 50mL of hydrochloric acid in the 100mL graduated

cylinder. 2. Pour the HCl into an 250mL beaker.3. Place piece of carbon (charcoal) into the beaker of HCl and

observe reaction.4. Repeat steps 1-3 for silicon.

Results and Elaborations• We were disappointed that neither the silicon nor the carbon reacted at

all with the HCl.• We think that the reason they both didn’t react is because they both have

the same amount of valence electrons. So they probably would react similarly because they both have either four electrons to give or receive.

• During the experiment, we also unexpectedly made an interesting discovery. That in a liquid, silicon sinks whereas carbon floats. (This was true in HCl and in water (known from the first procedure in which water was used to find density.)

• We would also have liked to test both elements in a base such as NaOH, but we ran out of time.

Further Elaboration• Our next steps to further prove that carbon and silicon are composed of different

atoms would be to first test their solubility in water. Then we would attempt to look at it under a petro graphic microscope, to see the difference in their crystal formation. We are also considering performing a pH test but weren’t sure how well that would work with two solids.

• Since carbon comes in various states of hardness (diamond compared to graphite) our results may have varied if we had used a different variant of carbon than charcoal.

• Another thing we would have done was to research better, the various experiments we wanted to perform, as well as their results to see if we would get reactions that would prove our hypothesizes.

Conclusion

• Though our experiments were unsuccessful is proving our hypothesis, they did indicate several differences between the two elements, such as texture, buoyancy, and their shapes.

• Based on these finding and the researched information, we believe that the atoms of carbon and silicon are composed of different atoms.

Bibliography• Kenneth Barbalace. Periodic Table of Elements - Silicon – Si.

EnvironmentalChemistry.com. 1995 - 2009. Accessed on-line: 10/1/2009http://EnvironmentalChemistry.com/yogi/periodic/Si.html.

• Kenneth Barbalace. Periodic Table of Elements - Carbon – C. EnvironmentalChemistry.com. 1995 - 2009. Accessed on-line: 10/1/2009http://EnvironmentalChemistry.com/yogi/periodic/C.html.

• Silicon: http://en.wikipedia.org/wiki/Silicon• Carbon: http://en.wikipedia.org/wiki/Carbon• Silicon: http://www.chemicool.com/elements/silicon.html# • Carbon: http://www.chemicool.com/elements/silicon.html#