Silicon-Based Life… Can it exist ? Mona Phan Jimmy Hoang CH 226H Spring ‘07

Life with Silicon

Star Trek!!!

Silicon Si, 14Si, 14 MetalloidMetalloid 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%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), silicatesilicon dioxide (silica/quartz), silicate metabolism of plants- grassmetabolism of plants- grass

Uses of Silicon Semiconductors: Transistors, solar cells, and other electronic solid-state devicesSemiconductors: Transistors, solar cells, and other electronic solid-state devices SiliconesSilicones Silica (Glass)Silica (Glass) Computer ChipsComputer Chips Concrete/BricksConcrete/Bricks Medicine/AestheticMedicine/Aesthetic

Forms of Silicon Granular silicon Polycrystal silicon Silicon monocrystal Nanocrystalline Silicon

Carbon and Silicon Similarities

Structure Group 4A elementsGroup 4A elements Forms 4 covalent bondsForms 4 covalent bonds Covalent networkCovalent network Quartz (Si and O atoms) CarbonSilicon

High Melting Point Carbon : 3527 °CCarbon : 3527 °C Silicon : 1414 °CSilicon : 1414 °C The “Z Machine”

Weak Conductors SemiconductorsSemiconductors must overcome an energy barrier known as the band gapmust overcome an energy barrier known as the band gap

Insoluble in water covalent bondingcovalent bonding

Why Not Silicon? “seems” like an ideal substitute for Carbon.“seems” like an ideal substitute for Carbon. Bonding Chemistry is similar with four covalent bonds.Bonding Chemistry is similar with four covalent bonds. However…However…

Major Differences Carbon is seen in sugars, DNA, and fatty acids in the body.Carbon is seen in sugars, DNA, and fatty acids in the body. Silicon simply can’tSilicon simply can’tcompete.

Major Differences Silicon compounds are usually very unstable and never occur in natureSilicon compounds are usually very unstable and never occur in nature Largest Silicon Chain is 6Largest Silicon Chain is 6 Carbon chains can go up in the thousands.Carbon chains can go up in the thousands.

Major Differences Old stars explode to form heavy elements.Old stars explode to form heavy elements. Heavy elements then produce other light elements. Overall carbon is produced more than siliconHeavy elements then produce other light elements. Overall carbon is produced more than silicon Carbon is abundant.Carbon is abundant.

Can Silicon-Based Life exist? Sadly, probably not.Sadly, probably not. However, silicon did play a role in the origins of life on earth.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 right- handed conformationscarbon molecules found naturally in left or right- handed conformations biochemical reactions of lifebiochemical reactions of life few silicon compounds have handednessfew silicon compounds have handedness Dihydroxyacetone

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