Hydrogen (Descriptive Chemistry)

It has 1 electron like Group 1 elements (alkali metals) But it’s a non-metal, forms covalent bonds, and can gain or lose electrons Sometimes compared to Group 17 (halogens) — forms H⁻ ions too!

By reacting a metal with a dilute acid: Zn + 2HCl → ZnCl₂ + H₂

During electrolysis of acidified water (usually with dilute H₂SO₄): Water is split into hydrogen and oxygen At the cathode (-): 👉 2H⁺ + 2e⁻ → H₂ (gas is released) At the anode (+): 👉 4OH⁻ → O₂ + 2H₂O + 4e⁻ 📌 So hydrogen gas forms at the cathode, oxygen at the anode.

Bring a lit splint near the gas → it gives a ‘pop’ sound (because hydrogen combusts rapidly in oxygen)

Colorless, odorless, tasteless gas Lightest element (diatomic molecule H₂) Can be liquified by compression and cooling

Highly flammable Forms covalent and ionic compounds Combusts in oxygen: 2H₂ + O₂ → 2H₂O Forms ionic hydrides with group 1A + 2A metals Forms interstitial hydrides with transitional metals Reduces metallic oxides to metals at high temperatures (WO₃ + 3H₂→W + 3H₂) Can reduce double C-C bonds in saturated organic compounds in the presence of Ni (high temp) or Platinum/Palladium (room temp)

Fuel in hydrogen fuel cells Making ammonia (Haber process) Hydrogenation of oils - manufacturing of margarine Rocket fuel Extraction of metals from their metal oxides Manufacture of HCl

Protium (¹H) – 1 proton, 0 neutrons (most common) Deuterium (²H / D) – 1 proton, 1 neutron Tritium (³H / T) – 1 proton, 2 neutrons (radioactive)

Hydrogen donates electrons (or removes oxygen) from other substances, reducing them. Examples: H₂ + CuO → Cu + H₂O (Hydrogen reduces copper(II) oxide to copper metal) Used in metal extraction and refining petroleum

Only reactive metals (e.g. Group 1) react with cold water: Metal + Water → Metal hydroxide + Hydrogen e.g. 2Na + 2H₂O → 2NaOH + H₂↑

Metal + Dilute Acid → Salt + Hydrogen e.g. Zn + 2HCl → ZnCl₂ + H₂↑

They form soluble complex ions: Aluminium: Al + NaOH + H₂O → Na[Al(OH)₄] + 1.5H₂↑ Zinc: Zn + 2NaOH → Na₂[Zn(OH)₄] + H₂↑

Group 1 & 2 metals (except Be) react with hydrogen gas: Metal + Hydrogen → Metal Hydride (ionic) e.g. 2Na + H₂ → 2NaH 🔑 These are basic, react with water to give H₂.

The stability of the hydrides of the elements from a group decreases with increasing atomic number

Its HI because the intermolecular forces are very weak compared to those in HCl

Compounds formed when hydrogen bonds with a transitional metal. (TiH)

Atomic hydrogen (H) is obtained by: Passing molecular hydrogen (H₂) through an electric arc or high-temperature plasma. This breaks the H–H bond, forming highly reactive atomic hydrogen (H). Atomic hydrogen is a powerful reducting agent

Nascent hydrogen is freshly produced hydrogen atoms (H) that form in situ (in the reaction mixture) before combining into H₂ gas. It is more reactive than molecular hydrogen (H₂) Exists only momentarily, often during reduction reactions

• Steam is passed over hot coke 2.The reaction is endothermic and the temperature drops • Air is blasted, and the temperature is raised C + H₂O→ CO + H₂ (endothermic) 2C + CO₂ + 4N₂ Water gas is treated with even more steam in the presence of a iron oxide catalyst Carbon monoxide is oxide to carbon dioxide and an extra mole of hydrogen is formed

• Cracking hydrocarbons • The manufacturing process of NaOH and Cl by electrolysing a solution NaCl • Passing steam over hydrocarbons

Covalent bond: shares 1 electron to get 1s² (e.g. H₂). Hydride ion (H⁻): gains 1 electron → 1s². Hydrogen ion (H⁺): loses its only electron → stable proton in solution