Hydrogen: Properties and Occurrence

• Group 1 and 2 elements belong to the s-block in the modern periodic table

Hydrogen (H)

• The first element in the periodic table
• Position is at the top of group 1 of the alkali metals
• Studied separately due to its differences from alkali metals
• Simplest atomic structure of all elements
• Exists as a diatomic molecule (H₂) and is called dihydrogen

Hydrogen Structure

• Contains a nucleus with a +1 charge
• Contains one extranuclear electron
• Exhibits a slight tendency to lose its electron
• Can easily form covalent bonds by pairing with another electron

Occurrence

• Exists as dihydrogen gas in the free state
• Most abundant element in the universe, accounting for 70% of the total mass
• Principal element in the solar system
• Tenth most abundant element on Earth by mass
• Third most abundant element on Earth by atom count

Position in the Periodic Table

• Electronic configuration is 1s¹
• Similar to the outer electronic configuration (ns¹) of Group 1 alkali metals
• Resembles the outer electronic configuration (ns²np⁵) of Group 17 elements
• Adding one electron results in the electronic configuration of the inert gas He (1s²)
• Adding one electron to ns²np⁵ results in ns²np⁶, the outer electronic configuration of the remaining inert gases
• Some chemical properties are similar to alkali metals, while others resemble halogens
• Hydrogen forms H⁺ ions when it loses an electron, always associated with other molecules
• Hydrogen is placed separately above Group 1

Discovery

• Metastable metallic hydrogen was discovered at Harvard University, USA, in January 2017

Isotopes of Hydrogen

• Different atoms of the element possessing varying mass numbers
• Three isotopes exist: Protium, Deuterium, and Tritium
• All contain one proton and one electron
• Varying numbers of neutrons in the nucleus

Isotope Properties

• Hydrogen (Protium, ¹H): Atomic number 1, mass number 1, 0 neutrons, abundance 99.98%, stable
• Deuterium (²H): Atomic number 1, mass number 2, 1 neutron, abundance 0.015%, stable
• Tritium (³H): Atomic number 1, mass number 3, 2 neutrons, trace abundance, radioactive

Tritium

• Radioactive nuclide
• Half-life of 12.4 years
• Emits low-energy beta particles

Preparation of Dihydrogen (H₂)

• Can be prepared via laboratory and industrial methods

Laboratory Methods

• Reaction of dilute hydrochloric acid with zinc granules: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
• Reaction of aqueous sodium hydroxide solution with zinc: Zn(s) + 2NaOH(aq) → Na₂ZnO₂(aq) + H₂(g)

Industrial Methods

• Electrolysis of Pure Water:Adding acid allows dihydrogen production via electrolysis.
• Electrolysis of dilute sulfuric acid yields two volumes of hydrogen at the cathode and one volume of oxygen at the anode
• Electrolysis of warm barium hydroxide solution between nickel electrodes gives very pure dihydrogen (> 99.5%)

From Carbon or Hydrocarbon

• Stage 1: React steam on hydrocarbon or coke at 1270 K with a nickel catalyst making water-gas, a mix of carbon monoxide and hydrogen. CH₄(g) + H₂O(g) → CO(g) + 3H₂(g)
• Water-gas, or syngas, is used to synthesize CH3OH and other hydrocarbons, vital for coal gasification, C(s) + H₂O(g) → CO(g) + H₂(g) Also, use sawdust or scrapwood can
• Stage 2: Transform CO in water-gas into carbondioxide reacting with steam using an iron chromate catalyst, known as the water-gas shift reaction: CO(g) + H₂O(g) → CO₂(g) + H₂(g)
• Stage 3: Scrub carbon dioxide which has been transformed, using a sodium arsenite solution

Production Method Percentages

• 77% from petrochemicals
• 18% from coal
• 4% by electrolytic methods
• 1% by other methods

Properties of Dihydrogen

Physical

• Colorless, tasteless, and odorless gas
• Burns with a pale blue flame
• Nonpolar and insoluble in water
• Lighter than air

Chemical

• Reacts with metals like alkali metals, calcium, strontium, and barium at high temperatures to form metal hydrides: 2Na(s) + H₂(g) → 2NaH(s)
• Reacts with dioxygen to form water in the presence of a catalyst or by heating and is highly exothermic: 2H₂(g) + O₂(g) → 2H₂O(l)
• Reacts with halogens, inflaming with fluorine even at -250°C in the dark, requiring a catalyst with iodine, with reactivity decreasing down the halogen
• Reduces oxides and ions of metals less reactive than iron at moderate temperatures: CuO(s) + H₂(g) → Cu(s) + H₂O(l), Fe₃O₄(s) + 4 H₂(g) → 3Fe(s) + 4H₂O(l), Pd²⁺(aq) + H₂(g) → Pd(s) + 2H⁺(aq)
• Hydrogenation of unsaturated organic compounds using a nickel catalyst produces saturated compounds like solid fat (vanaspati ghee): C=C + H₂ → CH-CH

Uses of Dihydrogen

• Largest use is in the production of ammonia
• Used for catalytic hydrogenation of oils such as fats to form vanaspati ghee
• Liquid dihydrogen is a rocket fuel
• Used in the preparation of organic compounds like methanol with a cobalt catalyst: 2H₂(g) + CO(g) → CH₃OH(l)
• Used to prepare hydrogen chloride (HCl) and metal hydrides

Group 1 and 2 Elements

Introduction

• Group 1 and 2 elements are on the left side of the periodic table
• Last electrons enter the "ns" subshell which is why they belong to the s-block

Group 1 Elements

• Consist of hydrogen, lithium, sodium, potassium, rubidium, caesium, and francium
• Except for hydrogen, they are collectively called alkali metals
• Sodium and potassium are the sixth and seventh most abundant elements in the Earth's crust
• Francium does not occur appreciably in nature because it is radioactive and has a short half-life

Group 2 Elements

• Consists of beryllium, magnesium, calcium, strontium, barium, and radium
• Called alkaline earth metals because they occur as minerals in rocks
• Magnesium and calcium are abundant in the Earth's crust
• Radium is one of the first two radioactive elements discovered by Marie Curie

Electronic Configuration

Group 1

• General outer electronic configuration is ns¹

Group 2

• General outer electronic configuration is ns²
• Loosely held s-electrons in the valence shell can be easily removed to form metal ions.
• Elements are never found in free state in nature

Physical Properties

Group 1

• Silver white and soft
• Low density because of their large atomic size
• Most electropositive elements

Group 2

• Metals are generally silvery white and lustrous
• Softer but harder than the alkali metals
• Strongly electropositive but comparatively less than the alkali metals
• Atomic and physical properties

Reactivity

• Alkali metal and alkaline earth metals are reactive in nature
• They are always found in a combined state
• Reactivity can be attributed to their low ionization enthalpy values
• Reactivity of these metals increases with increasing atomic radius and corresponding lowering of ionization enthalpy down the groups 1 and 2

Group 1 Reaction with Oxygen/Air

• Elements tarnish rapidly in air
• Form oxides, peroxides and in some cases superoxide
• 2Li + O₂ → 2LiO (Lithium oxide)
• 2Na + O₂ → Na₂O₂ (Sodium peroxide)
• K + O₂ → KO₂ (Potassium superoxide)
• Alkali Superoxides have the ability to absorb carbon dioxide and give out oxygen: 4KO₂ + 2CO₂ → 2K₂CO₃ + 3O₂↑
• Used in breathing equipment for mountaineers, submarines, and space

Reactions with Halogens

• React vigorously to produce ionic halide salts: 2M + X₂ → 2M⁺X⁻

Solubility in Liquid Ammonia

Group 1

• Soluble in liquid ammonia & conduct electricity: M + (x + y)NH₃ → [M(NH₃)ₓ]⁺ + [e(NH₃)ᵧ]

Reactions with Water

• Lithium reacts slowly but sodium and potassium react: vigorously with water, Sodium and potassium catch fire when put in water via highly exothermic reaction: 2Na + 2H₂O → 2Na OH + H₂↑

Reactions with Hydrogen

• Alkali metals react with hydrogen at high temperatures to form the corresponding metal hydrides: 2M + H₂ → 2M⁺ H⁻

Group 2 Reactions with Water

• Group 2 elements react with water to form metal hydroxides and hydrogen.
• Beryllium does not react with water.
• Magnesium decomposes hot water and other elements reacts with cold water to form metal hydroxide M(OH)₂, Ca + 2H₂O → Ca(OH)₂ + H₂

Group 2 Reactions with Hydrogen

• Except for beryllium, all form MH₂ type hydrides: M + H₂ → MH₂

Group 2 Reaction with Halogens

• Alkaline earth metals combine with halogens at high temperature, M + X₂ → MX₂

Group 2 Solubility in Liquid Ammonia

• Give deep blue black colored solutions
• Group 2 elements have general form : M + (x + 2y) NH₃ → [M(NH₃)ₓ]²⁺ + 2[e(NH₃)ᵧ]

Diagonal Relationship

Lithium

• The first alkali metal
• Beryllium is the first alkaline earth metal
• Elements belonging to the same group exhibit similarity and gradation in their properties
• Lithium and beryllium do not fulfil this expectation

Lithium

• Lithium shows many differences when compared with the remaining alkali metals and resembles magnesium, which is the second alkaline earth metal

Beryllium

• Beryllium shows many differences with remaining alkaline earth metals and shows similarity with aluminium which is the second element of the next main group
• Elements with similar properties appear placed diagonally relative to each other in the periodic table

Resemblance between Li and Mg

• Products with air Li₂O and Li₃N
• Products with decomposition of carbonate Li₂O and CO₂

Resemblance between Be and Al Properties of Chloride

• Whether Lewis acid ; Soluble in organic solvent and can be used Be : Covalent chain structure; BeCl strong Lewis acid & Soluble Al : Dimer with Cl bridges; AlCl is strong Lewis acid & Soluble

Uses of Group 1 - Lithium

• Metal is used in long-life batteries
• Used in digital watches, calculators and computers

Uses for Group 1 - Liquid Sodium

• Heat transfer in nuclear power station

Uses for Group 1 - Potassium

• Chloride is used as a fertilizer
• Is used in manufacturing potassium superoxide: for oxygen generation
• Good absorbent of carbon dioxide and gives out oxygen at the same time: 4KO₂ + 2CO₂ → 2K₂CO₃ + 3O₂↑ Used in the process of in breathing equipment
• Used in breathing equipment for mountaineers, submarines, and space
• Chloride also is used as a fertilizer.
• Potassium superoxide which is good absorbent of carbon dioxide
• Caesium: Used in photoelectric cells

Uses for Group 2 - Beryllium

• Moderator in nuclear reactors

Uses for Group 2 - Magnesium and aluminum

• Alloy of magnesium and aluminum which is widely used as structural material and in aircrafts

Uses for Group 2 - Calcium

• Calcium ions are important ingredient in biological system to produce a healthy growth of bones and teeth

Uses for Group 2 - Barium

• Barium Sulphate is used in medicine as barium meal for intestinal x-ray

Group 1 Biological Importance - Sodium

• Sodium has a supply in all extracellular fluids which for transporting nutrients
• The concentration extracellular fluids regulates water flow across the membrane, participate in transmission of nerve signals
• Potassium ions are in the most cells
• Are required for maximum efficiency in synthesizing proteins and with oxidation of glucose

Group 1 Biological Importance - Magnesium

• Are an important part of chlorophyll in green plants and role in the breakge of glucose and in synthesis of proteins, with enzymes and in level of cholesterol
• Calcium ions are important for bones, teeth, blood clotting, with contraction and stretching of muscles
• Are required to maintain regular beating of the heart

Sodium Carbonate

• Produced by passing carbon dioxide into concentrated sodium chloride and ammonia, producing sodium bicarbonate crystals
• Bicarbonate crystals are then heated to yield the carbonate, and ammonium chloride is used to obtain sodium carbonate: 2 NH₃(aq) + H₂O + CO₂(g) → (NH₄)₂ CO₃(aq) , (NH₄)₂CO₃(aq) + H₂O + CO₂(aq) 2 NH₄HCO₃(aq) , NH₄HCO₃(aq) + NaCl(aq) NH₄Cl(aq) + NaHCO₃(s)
• Sodium carbonate solution used

Equation to make Sodium Carbonate

• 2 NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g)

Calcium carbonate

• Cannot be precipitated for Solvay since highly soluble with potassium of chorine

Properties of Sodium Carbonate

• Has alkaline, effects on emulsifying grease and cleaning of oil
• Is used in hard water & used with soluble water
• Has alkalinity which is responsible for its emulsifying effect
• Is used to with commercial production of soap and caustic soda
• Important laboratory reagent

Properties of Sodium Hydroxide

• Is in deliquescent form with high melting point
• Highly soluble and dissolves with solution
• Sodium is used in Bauxite

Properties of Calcium Carbonate

• Found in nature to form chalk
• Is practically insoluble and heating produces carbon dioxide: CaCO₃(s) → CaO(s) + CO₂↑
• The carbonate of calcium is found in chalk form

Properties of hydrogen peroxide

• Subjected to electrolysis forms perdoxsulfuric at anode
• Has a pure and pale liquid form that is miscible for forming a hydrate.
• Is used with volume and can be a solution
• Has a oxidizing and reducing agent

Properties lithium aluminium hydride

• Is used to prepare PH₃, and forms AlCL₃ with LICI
• AlH is a reducing agent and a for of hydride to product organic synthesis