Ch 4Hydrogen — Class 11 Chemistry, concept-first.

Hydrogen is deceptively simple to describe -- one proton, one electron -- yet it doesn't fit neatly into any single group of the periodic table, and it is the third most abundant element on the surfac…

Hydrogen is the simplest atom in the periodic table: its nucleus is a single proton, orbited by a single electron.

Hydrogen's electronic configuration is -- one electron in the first shell. This matches the general valence-shell pattern of the alkali metals (Li: , Na: , K: , ...), and hydrogen indeed behaves like…

Hydrogen has three naturally-occurring isotopes -- atoms with the same one proton (and hence the same atomic number, 1) but different numbers of neutrons:

Every hydrogen nucleus (a lone proton) has a nuclear spin. When two hydrogen atoms combine to form the H₂ molecule, the spins of the two nuclei can point in the same direction or in opposite direction…

The purest hydrogen -- greater than 99.9% -- is obtained by electrolysis: either water containing a trace of acid or alkali to make it conducting, or an aqueous solution of sodium hydroxide or potassi…

The hydrogen used in a school or college laboratory is conveniently generated by letting an active metal -- zinc, iron or tin are the ones typically used -- react with a dilute mineral acid.

On the industrial scale, hydrogen is produced chiefly by steam-reforming of hydrocarbons. A hydrocarbon such as methane is mixed with steam and passed over a nickel catalyst at 800-900°C and about 35…

Ordinary (normal) water already contains a tiny natural proportion of heavy water -- about D₂O. The key to concentrating this trace into usable deuterium is a kinetic difference: protium water (H₂O) d…

Because tritium occurs in nature only as an extreme trace, it must be manufactured artificially rather than isolated from a natural source.

Having seen how dihydrogen, deuterium and tritium are prepared, the unit now turns to what hydrogen is actually like -- its physical character (Section 4.3.1) and its characteristic chemical reactions…

Hydrogen gas (H₂) is colourless, odourless and tasteless. It is the lightest gas known and is highly flammable. As a diatomic molecule made of two identical atoms, it is non-polar.

Reaction with oxygen. Hydrogen combines with oxygen to give water, in a strongly exothermic, explosive reaction -- the same reaction that is harnessed inside a hydrogen fuel cell to generate electrici…

Deuterium's chemistry closely parallels ordinary hydrogen's. Like H₂, it reacts with oxygen to form the deuterium analogue of water -- deuterium oxide, better known as heavy water:

Tritium's chemistry is dominated by one overriding fact: it is radioactive. It decays as a β-emitter, with a half-life of 12.3 years, converting into helium-3 and releasing a beta particle (an electro…

Hydrogen's uses span synthesis, metallurgy, energy and beyond:

Beyond the element itself, hydrogen forms a set of compounds important enough to study individually: ordinary water, hard and soft water, heavy water, and hydrogen peroxide -- covered in this order be…

Water (H₂O) is the single most abundant compound of hydrogen. The earth's surface is roughly 70% ocean, making the sea the major reservoir of water on the planet -- though sea water carries so many di…

Water is a colourless, volatile liquid. Many of its familiar but, on reflection, unusual bulk properties in the liquid and solid states -- an unexpectedly high melting point and boiling point for so s…

Water's chemical behaviour depends strongly on what it is reacting with.

What makes water "hard". Hard water carries high concentrations of dissolved mineral ions -- most commonly the soluble cations of magnesium and calcium, though iron, aluminium and manganese can also c…

Heavy water (D₂O) is the oxide of "heavy hydrogen" -- deuterium. In ordinary water, only about one part in 5000 is naturally heavy water.

Hydrogen-deuterium exchange. When a compound containing hydrogen is treated with D₂O, its hydrogen atoms undergo an exchange with deuterium:

Heavy water has three principal uses, all exploiting properties distinct from ordinary water:

Hydrogen peroxide (H₂O₂) ranks among the most important of all peroxides. It can be prepared in the laboratory by treating a metal peroxide with a dilute acid:

Pure hydrogen peroxide is an almost colourless liquid, though it has a faint pale-blue tint in bulk. It is less volatile and more viscous than water.

Hydrogen peroxide is inherently unstable: its aqueous solution spontaneously disproportionates into water and oxygen.

Hydrogen peroxide's usefulness rests on a combination of two facts: it is a genuinely effective oxidising agent, yet the by-products of that oxidation -- water and oxygen -- are completely harmless.

Both in the gas phase and in the solid phase, the H₂O₂ molecule adopts a skewed, non-planar conformation -- the two O-H bonds are twisted out of a single plane rather than lying flat, because of the r…

Hydrogen forms binary hydrides -- compounds of hydrogen with one other element -- with a great many electropositive elements, both metals and non-metals.

Hydrogen bonding is one of the most important interactions in both chemistry and biology. It arises whenever a hydrogen atom is covalently bonded to a small, highly electronegative atom -- fluorine, o…

Sample papers and previous-year board questions for this subject.