Transcript Carbon Silicon

Silicon-Based Life… Can it exist?
Mona Phan
Jimmy Hoang
CH 226H Spring ‘07
Life with Silicon
Star Trek!!!
Silicon
• Si, 14
• Metalloid
• Earth’s Crust composition by mass: Oxygen: 46.6 %,
Silicon: 27.7%, Aluminum: 8.1%, Iron: 5%, Calcium:
3.6%, Sodium: 2.8%, Potassium: 2.6%, Magnesium:
2.1%
• silicon dioxide (silica/quartz), silicate
• metabolism of plants- grass
Uses of Silicon
• Semiconductors: Transistors, solar cells,
and other electronic solid-state devices
• Silicones
• Silica (Glass)
• Computer Chips
• Concrete/Bricks
• Medicine/Aesthetic
Forms of Silicon
Granular silicon
Silicon monocrystal
Polycrystal silicon
Nanocrystalline Silicon
Carbon and Silicon
Similarities
Structure
• Group 4A elements
• Forms 4 covalent bonds
• Covalent network
Quartz (Si and O atoms)
Carbon
Silicon
High Melting Point
• Carbon : 3527 °C
• Silicon : 1414 °C
The “Z Machine”
Weak Conductors
• Semiconductors
• must overcome an
energy barrier
known as the band
gap
Insoluble in water
• covalent bonding
Why Not Silicon?
• “seems” like an ideal substitute for
Carbon.
• Bonding Chemistry is similar with four
covalent bonds.
• However…
Major Differences
• Carbon is seen in sugars, DNA, and
fatty acids in the body.
• Silicon simply can’t
compete.
Major Differences
• Silicon compounds are usually very
unstable and never occur in nature
• Largest Silicon Chain is 6
• Carbon chains can go up in the
thousands.
Major Differences
• Old stars explode to form heavy
elements.
• Heavy elements then produce other
light elements. Overall carbon is
produced more than silicon
• Carbon is abundant.
Can Silicon-Based Life exist?
• Sadly, probably not.
• However, silicon did play a role in the
origins of life on earth.
Chirality
“handedness”
Chirality of Carbon vs. Silicon
• carbon molecules found naturally in left or righthanded conformations
• biochemical reactions of life
• few silicon compounds have handedness
Dihydroxyacetone
Ask the Experts
Silicon-Based Life Mechanics