Chemistry in Context - Portable Electronics

The Periodic Table and Chemical Symbols

• Elements are represented by 1- or 2-letter abbreviations.
• Most symbols are straightforward (e.g., O = oxygen, Si = silicon).
• Some symbols are based on Latin or Greek names:
  • Pb = lead (plumbum in Latin)
  • Hg = mercury (hydrargyrum in Greek)
  • Cu = copper (cuprum in Latin)
  • Fe = iron (ferrum in Latin)
  • K = potassium (kalium in Latin)
  • Sb = antimony (stibium in Latin)
  • Ag = silver (argentum in Latin)
  • Au = gold (aurum in Latin)

Organization of the Periodic Table

• Elements are organized into groups (columns) and periods (rows).
• Metals, nonmetals, and metalloids:
  • Most elements are metals.
  • Metalloids include: B, Si, Ge, As, Sb, Te, Po.
  • The periodic table organizes elements by increasing atomic number and groups elements with similar properties.

Groups of the Periodic Table

• Group 1: Alkali metals
• Group 2: Alkaline earth metals
• Group 15: Pnictogens
• Group 16: Chalcogens
• Group 17: Halogens
• Group 18: Noble gases

Classification of Matter

• Four components of matter: solids, liquids, gases, and plasmas.
• Matter can be divided into:
  • Pure substances: elements and compounds
  • Mixtures: heterogeneous and homogeneous
• Elements: contain atoms of the same type (e.g., silicon (Si))
• Compounds: contain 2 or more different types of atoms (e.g., silicon dioxide (SiO2))
• Mixtures:
  • Heterogeneous: composition varies throughout (e.g., gravel)
  • Homogeneous: uniform composition throughout (e.g., sugar dissolved in water)

Examples of Classifying Matter

• Carbon dioxide (CO2): compound
• Nickel (Ni): element
• Ammonia (NH3): compound
• Water (H2O): compound
• Fluorine (F2): element
• Table salt (NaCl): compound
• Soap (various organic compounds): mixture
• Sea water (salts dissolved in water): mixture

Law of Multiple Proportions

• Elements combine in integer ratios to form multiple compounds with different properties.
• Example: Iron oxides
  • $Fe3O4$ (magnetite): magnetic
  • $Fe2O3$ (rust): not magnetic

Atoms and the Building Blocks of Matter

• Ionic compounds: composed of oppositely charged ions (electrons added or subtracted from atoms).
• Molecular compounds: composed of molecules made up of atoms.
• Scales of matter:
  • Macroscopic: viewable with the naked eye (states of matter, elements, compounds, mixtures)
  • Sub-microscopic/nanoscale: individual molecules, ions, and atoms (one-billionth of a meter)

Properties of Subatomic Particles

• Proton:
  • Relative charge: +1
  • Relative mass: 1
  • Actual mass: $1.67 \times 10^{-27}$ kg
• Neutron:
  • Relative charge: 0
  • Relative mass: 1
  • Actual mass: $1.67 \times 10^{-27}$ kg
• Electron:
  • Relative charge: -1
  • Relative mass: 0 (approximate)
  • Actual mass: $9.11 \times 10^{-31}$ kg
• Most of the mass in an atom is found in the nucleus (protons and neutrons).
• Electrons are located outside the nucleus.

Atomic Structure Examples

• Hydrogen Atom:
  • Atomic #: 1 (1 proton)
  • Mass #: 1 (1 proton, 0 neutrons)
• Helium Atom:
  • Atomic #: 2 (2 protons)
  • Mass #: 4 (2 protons, 2 neutrons)
• For neutral atoms: # electrons = # protons (charges must balance)

Electrical Conductivity of Metals

• Metals are electrically and thermally conductive.
• Electrical conductivity involves the movement of electrons through the 3-D structure of a conductor.

How Touchscreens Work

• Touchscreens contain 2-D grids of metallic wires sandwiched between two insulating layers.
• Electrical current flows in the wires and is stored within this multilayer structure.
• Touching the screen with a conductive object (finger) distorts the electrical field.
• The location of the touch is determined by a controller in the processing chip.

From Mineral to Metal: Aluminum from Bauxite Ore

• Metals are isolated from natural rock formations.
• Example: Aluminum from bauxite ore.
• 200.0 g bauxite contains:
  • 100.0 g gibbsite
  • 50.5 g boehmite
  • 49.5 g iron oxide
• Percentage composition:
  • Gibbsite: $\frac{100.0 \text{ g}}{200.0 \text{ g}} \times 100\% = 50.00\%$
  • Boehmite: $\frac{50.5 \text{ g}}{200.0 \text{ g}} \times 100\% = 25.3\%$
  • Iron oxide: $\frac{49.5 \text{ g}}{200.0 \text{ g}} \times 100\% = 24.7\%$

Significant Figures

• All non-zero digits are significant (e.g., 1.55 g = 3 sig figs).
• Zeroes embedded between non-zero digits are significant (e.g., 1.003 mL = 4 sig figs).
• Trailing zeroes are significant (e.g., 1.000 g = 4 sig figs).
• Leading zeroes are not significant (e.g., 0.00305 mL = 3 sig figs).
• Addition/subtraction: answer based on smallest # decimal places.
  • e.g., 1.003 g + 0.2 g + 0.001 g = 1.2 g
• Multiplication/division: answer based on smallest # sig figs.
  • e.g., $1.002 \text{ cm} \times 0.005 \text{ cm} = 0.005 \text{ cm}^2$

Minerals as Primary Source of Metals

• Earth’s crust predominantly composed of O, Si, Al, and alkali/alkaline earth metals.

From Sand to Silicon: Reduction-Oxidation (Redox) Reactions

• Oxidation: Electrons removed from a metal
  • $M \rightarrow M^+ + ne^-$ e.g., $4Al(s) + 3O<em>2(g) \rightarrow 2Al</em>2O_3(s)$
  • Formally (aluminum is oxidized): $Al^0 \rightarrow Al^{3+} + 3e^-$
• Reduction: Electrons added to a metal/compound
  • $M + ne^- \rightarrow M^-$ e.g., $SiO_2(s) + C(s) \xrightarrow{1000 ^\circ C} 2CO(g) + Si(s)$
  • Formally (silicon is reduced): $Si^{4+} + 4e^- \rightarrow Si$

Silicon Purification

• Silicon obtained from the reduction of sand undergoes further purification.
• Step 1: $Si(s) + 3HCl(g) \xrightarrow{300 ^\circ C} SiHCl<em>3(g) + H</em>2(g)$
• Step 2: $2SiHCl<em>3(g) \xrightarrow{1150 ^\circ C} Si(s) + 2HCl(g) + SiCl</em>4(g)$
• This results in ultra-high purity silicon, referred to as “12N Purity”.
• 12N purity: 99.9999999999% silicon (only $1 \times 10^{-10}\%$ of impurities).

Scientific Notation

• Small numbers: move decimal to the right.
• Large numbers: move decimal to the left.
• Examples:
  • $11000 = 1.1 \times 10^4$
  • $0.00021 = 2.1 \times 10^{-4}$
  • $0.001021 = 1.021 \times 10^{-3}$
  • $1730 = 1.73 \times 10^3$
  • $6.022 \times 10^{-23} = 0.00000000000000000000006022$
  • $602,200,000,000,000,000,000,000 = 6.022 \times 10^{23}$

Ultra-High Purity (UHP) Silicon Analogy

• Stack 170 yellow tennis balls from Earth to the moon.
• Replace 1 yellow tennis ball with a red one.
• This reflects the low impurity level in ultra-high purity silicon.

From Silicon to Computer Chip

• (a) Ultra-high purity silicon (5N, 7N, or 12N purity).
• (b) At high temperatures, silicon is fabricated into cylinders (ingots) & sliced into wafers.
• (c) Hundreds of processing steps are used to fabricate a computer chip on the surface of silicon wafers.
• (d) Chips are removed from the wafer and tested.
• (e) The chips that are tested satisfactorily are sealed and packaged.
• Technicians work inside "clean rooms" and wear "bunny suits" to prevent contamination by dust particles.

Inside a Processing Chip

• Computer chips contain billions of tiny components (transistors).
• Transistors perform calculations for computers and portable electronic devices.
• The scale bars in electron microscope images are comparable to:
  • (a) Diameter of a cloud water droplet
  • (b) Diameter of mold spores
  • (c) Diameter of a human hair fiber
  • (d) Diameter of beach sand
  • (e) Thickness of a human cornea
  • (f) Diameter of a pinhead
  • (g) Diameter of a pupil

From Sand to Glass

• Sand (SiO2) is used as a precursor to silicon and for glassmaking.
• Sand is a colorless solid; colored crystals result from other metals in the crystal structure.

From Crystalline Sand to Amorphous Glass

• (a) Quartz sand is a crystalline solid (ordered 3-D structure).
• (b) Glass is a disordered solid (amorphous).

Glassmaking Process

• Sand is heated to temperatures >$1000 ^\circ C$ and cooled rapidly to form a disordered glass.
• Quartz sand has a high melting point (>1300 ^\circ C).
• Additives (sodium carbonate, $Na<em>2CO</em>3$, calcium carbonate, $CaCO<em>3$, magnesium carbonate, $MgCO</em>3$) are used to lower the melting point.

Crack-Resistant Glass

• To strengthen glass, sodium ($Na^+$) ions are replaced with larger potassium ($K^+$) ions at high temperature.
• This forms a compression layer on the surface of the glass.
• Normal glass can withstand a force of 7,000 psi.
• Gorilla Glass™ can withstand >100,000 psi.

Cradle-to-Cradle Recycling

• Sustainable life cycle for portable electronics: "cradle-to-cradle" recycling.
• End-of-life of one product becomes the beginning of the life cycle for another product.
• Over 90% of cell phones are sent to landfills or are collected at homes.
• Only 3% are recycled.

The Three Pillars of Sustainability

• Environmental: pollution prevention, natural resource use.
• Social: better quality of life for all members of society.
• Economic: fair distribution and efficient allocation of resources.

Portable Electronics: Operating vs. Fabrication Costs

• An iPhone consumes 152 kWh of electricity over its lifetime (546 MJ of energy).
• 464 MJ from production (not counting energy needed to extract, refine, and transport raw materials).
• Compare this with the energy contained in 1 gallon of gasoline (131 MJ).
• As electronic devices get smaller, they consume less energy but are more expensive to produce.

The Rare Earth Metals: A Needed Resource

• Rare earth metals are used for vehicle catalytic converters, fluorescent lighting, memory chips, rechargeable batteries, magnets, speakers, advanced weaponry, and advanced electronics.

Where Are the Rare Earths?

• China controls most of the world’s supply of rare earth metals.
• The U.S. is reliant on other countries’ exports of these elements.
• Questions raised: Are there alternatives? What if trade wars develop?