Chemistery

Here is a fact that quietly breaks a rule you learned early on. Two bottles on a shelf: one holds a gas that boils at −0.5 °C, the other a gas that boils at −11.7 °C. They are different compounds with different properties. And both have the molecular formula C₄H₁₀ . The short answer: isomers are compounds with the same molecular formula but different arrangements of atoms . Because chemical behaviour depends on how atoms are connected and positioned in space — not merely on how many of each there are — isomers are genuinely different substances with different physical and chemical properties. What a molecular formula leaves out A molecular formula is an inventory: C₄H₁₀ says four carbons and ten hydrogens. It says nothing about which carbon is joined to which. Once a molecule has four or more carbons, there is usually more than one legal way to wire them up. For C₄H₁₀ there are exactly two: Butane — a straight chain, CH₃–CH₂–CH₂–CH₃. Boils at −0.5 °C. 2-methylpropane — a th...

Cyclohexane and benzene look almost like the same molecule: both are six-carbon rings, differing by six hydrogens. Yet cyclohexane is a forgettable solvent and benzene is a whole separate branch of organic chemistry with its own rules and its own reactions. The word that separates them is aromatic . The short answer: aromatic compounds contain a flat, fully conjugated ring whose π electrons are delocalised around the whole ring, giving unusual stability; aliphatic compounds are everything else organic — chains, branches and non-aromatic rings. The practical consequence is that aromatic rings undergo substitution to preserve their delocalisation, while unsaturated aliphatic compounds undergo addition . Quick comparison at a glance Feature Aliphatic Aromatic Structure Open chains, branches, non-aromatic rings At least one aromatic ring Includes Alkanes, alkenes, alkynes, cycloalkanes and cycloalkenes Benzene, toluene, naphthalene, pyridine π electrons Localised in individua...

There are more than a hundred million known organic compounds. Nobody memorises how each one behaves — and nobody has to, because the chemistry of an organic molecule almost never depends on the whole molecule. It depends on one small reactive patch. That patch is the functional group . The short answer: a functional group is a specific arrangement of atoms within a molecule that is responsible for that molecule's characteristic chemical reactions. Molecules sharing the same functional group react in the same ways, which is why organic chemistry can be learned as a few dozen groups instead of millions of compounds. What "functional" really means Think of a hydrocarbon chain as scaffolding. It is nonpolar, unreactive toward most reagents, and chemically boring — which is exactly what makes it useful as a backbone. Now swap one hydrogen for an –OH group and everything changes: the molecule can hydrogen-bond, its boiling point jumps, a short-chain one dissolves in wate...

Three families, three suffixes, and an exam question that always seems to hinge on which one decolourises bromine water. The good news is that alkanes, alkenes and alkynes differ in exactly one thing — how many bonds join two carbons — and everything else follows from that single fact. The short answer: alkanes have only C–C single bonds, alkenes contain a C=C double bond, and alkynes contain a C≡C triple bond. Adding bonds pulls the carbons closer, straightens the geometry, and adds reactive π electrons — which is why alkanes are sluggish while alkenes and alkynes readily undergo addition reactions. Quick comparison at a glance Feature Alkane Alkene Alkyne Carbon–carbon bond Single, C–C Double, C=C Triple, C≡C General formula CₙH₂ₙ₊₂ CₙH₂ₙ CₙH₂ₙ₋₂ Suffix -ane -ene -yne Hybridisation at that carbon sp³ sp² sp Bond angle ~109.5° ~120° 180° Bond length 154 pm 134 pm 120 pm Bond enthalpy ~347 kJ/mol ~614 kJ/mol ~839 kJ/mol σ and π bonds 1 σ 1 σ + 1 π 1 σ + 2 π Rotation...

Organic chemistry looks intimidating from the outside: thousands of compounds, strange names, mechanisms with curly arrows everywhere. But almost all of it is built on one small idea, and the simplest molecules in the whole subject are the place to meet it. Those molecules are the hydrocarbons . The short answer: a hydrocarbon is a compound made of carbon and hydrogen only — nothing else. They matter because carbon can bond to itself over and over, so a handful of atoms builds an endless family of chains, branches and rings that forms the skeleton of every organic molecule. Why carbon, of all elements Carbon sits in group 14 with four valence electrons , which means it forms four covalent bonds — the most it can make while staying neutral and stable. Two things follow from that, and together they explain organic chemistry. First, four bonds is enough to build outward in three dimensions rather than just forming a short chain that runs out of room. Second, the carbon–carbon sing...

Benzene melts at 5.5 °C and boils at 80.1 °C. Toluene — the same ring with a methyl group stuck on — boils higher , at 110.6 °C, but melts at a spectacular −95 °C . One molecule is bigger and holds on more tightly, yet it falls apart as a solid 100 degrees sooner. If melting and boiling measured the same thing, that could not happen. The short answer: the melting point is the temperature at which a solid becomes a liquid, and the boiling point is the temperature at which a liquid becomes a gas throughout its bulk — when its vapour pressure equals the surrounding pressure. Melting only loosens a structure enough to let particles slide; boiling has to pull them apart completely, which is why boiling point is a much better guide to intermolecular force strength. Quick comparison at a glance Feature Melting point Boiling point Phase change Solid → liquid Liquid → gas What must be overcome Enough of the lattice to let particles move past each other Essentially all the attractions be...