Hydrogen in Nature and the Hydrogen Cycle

• Topic is about hydrogen

Hydrogen in Nature

• Hydrogen makes up 92% of the universe
• Helium makes up 7%
• The remaining 1% is other elements
• Stars are composed of H₂ and H
• Interstellar space consists of H
• Hydrogen is the tenth most abundant element by weight in the Earth's crust
• H₂O covers 80% of the Earth's surface
• The human body is 70% hydrogen
• Hydrogen is found in organic compounds
• It is found in fossil fuels like petroleum and natural gas
• The stratosphere contains atomic hydrogen

Hydrogen Cycle

• Hydrogen is part of a biogeochemical cycle involving biotic and abiotic sources and sinks.
• Hydrogen is key to the water, carbon, nitrogen and sulfur cycles
• Evaporation is when water evaporates from land and sea surfaces
• During photosynthesis, plants use solar energy to combine H₂O and CO2 to produce glucose, releasing O2; hydrogen is part of glucose
• During respiration, animals and plants use O2 to break down glucose and produce energy, releasing H2O and CO2
• During fermentation, microorganisims make H2 from organic matter in anaerobic conditions
• Oxidation occurs when H₂ is oxidized by photochemical reactions

Importance of the Hydrogen Cycle

• Regulates the balance of hydrogen, essential for life and atmospheric chemistry
• Contributes to energy and organic matter through photosynthesis and respiration
• Involved in forming biofuels and fertilizers through fermentation and nitrogen fixation
• Implies early life evolution and prebiotic chemistry since hydrogen is most abundant and reactive

Hydrogen Element

• Hydrogen is key for life with specific properties
• Similar electronegativity to carbon is important
• It can form hydrogen bonds when binding covalently to nitrogen or oxygen
• Low C-H bond polarity stabilizes chemically reactive organic compounds

Hydrogen Properties

• It's a non-metal
• Hydrogen forms diatomic molecules (H₂)
• Hydrogen is less reactive than halogens (X₂)
• It doesn't react with water
• A hydrogen atom holds a single electron
• It can lose an electron to form H⁺
• It can gain an electron to form H⁻

Isotopes of Hydrogen

• Protium (¹H): Atomic weight of 1.0078 and relative abundance of 99.98%
• Deuterium (²H): Atomic weight of 2.0141 and relative abundance of 0.015%
• Tritium (³H): Atomic weight of 3.0160 and relative abundance of 10⁻¹⁷

Hydrogen Uses

• Production part
• Production of Metals
• Margarines
• Fertilizers and plastics
• Fuel
• Batteries of fuel such as rockets

Hydrogen Production (Laboratory Scale)

• M + H⁺ results in Mn⁺ + H₂; an example is Zn + HCl to ZnCl₂ + H₂.
• M + OH⁻ results in M(OH)n + H₂; an example is Al + NaOH to Na[Al(OH)₄] + H₂.
• M + H₂O results in M(OH)n + H₂; an example is Na + H₂O to NaOH + H₂.
• H⁻ + H₂O results in OH⁻ + H₂; an example is LiH + H₂O to LiOH + H₂.

Hydrogen production(Industrial scale)

• Reduction of water with hydrocarbons
• CH₄ (natural gas) + H₂O -> CO + H₂
• H₂O + CO -> CO₂ + H₂
• CO₂ + K₂CO₃(aq) -> 2KHCO₃(aq)

Electrolysis of Water

• 2 H₂O(l) + 2e⁻ -> H₂(g) + 2OH⁻(aq)
• 2 OH⁻(aq) - 2e⁻ -> 1/2 O₂(g) + H₂O(l)
• Electrolyte: 25% NaOH, 2-2.5V with nickel or iron electrodes

Hydrogen Derivatives

• Losing an electron creates H+
• Gaining results in H-
• Sharing results in E-H

Ionic Hydrides

• Occur when the electronegativity of M is less than H, resulting in H⁻
• M is G1 (group 1) and heavy G2 (group 2) elements

Properties of Ionic Hydrides

• They form three-dimensional ionic lattices
• Melting points exceed 600°C
• Conduct electricity when molten
• Electrolysis produces H₂ at the anode
• The method of obtaining is M + n/2 H₂ -> MHₙ

Metallic Hydrides

• Interstitial
• Stoichiometric: CrH and VH2 are examples
• Non-stoichiometric: TiH1.9 and HfH2.1 are examples

Metallic Hydride Properties

• Hard and brittle
• Metallic luster & Magnetic properties
• Conduct electricity, or semiconductive
• They absorb a large amount of H2, releasing it at will as a source of power.

Covalent Hydrides

• Molecular: Examples include CH₄, NH₃, H₂O, and HF.
• Polymeric: Examples include BeH₂ and B₂H₆

Covalent Hydrides Traits

• Electron deficient
• Tricentric

Hydrogen Bonds

• Hydrogen bonds are formed between X-H...Y
• X is very electronegative
• F > O > Cl > N > Br > I = S = C
• H is small, links better with small atoms

Water Molecule Dipole Nature

• Tetrahedral arrangement of O-H bonds and oxygen's lone electron pairs
• Hydrogen carries a partial positive charge, while oxygen carries a partial negative charge
• Hydrogen bonds form between water molecules

Ice Structure

• Each water molecule can form a maximum of four regular crystalline network hydrogen bonds
• In liquid water, each molecule forms an average of 3.4 hydrogen bonds with other water molecules
• Ice's crystalline network requires greater space than liquid water; therefore, frozen water is less dense and floats

Explore the abundance and distribution of hydrogen in the universe, Earth's crust, and the human body. Discover its role in stars, interstellar space, water, organic compounds, and fossil fuels. Understand the hydrogen cycle, its importance in biogeochemical cycles, and its involvement in water, carbon, nitrogen, and sulfur cycles.