Chemistery

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...

Leave a puddle of water and a puddle of nail-polish remover side by side on a warm day. The acetone is gone in minutes; the water takes hours. Neither one is being heated to its boiling point, and neither one is bubbling. What differs is a property you can put a number on — and the same number explains why you cannot make a decent cup of tea on a mountain. The short answer: vapour pressure is the pressure exerted by a substance's vapour when it is in dynamic equilibrium with its liquid in a closed container at a given temperature. It measures how strongly a liquid "wants" to escape into the gas phase: weak intermolecular forces and higher temperatures both mean higher vapour pressure. What vapour pressure actually measures Half-fill a sealed flask with water and watch what happens at the molecular level. At first, molecules with above-average energy break free of the surface and enter the space above. As that space fills with vapour, some of those molecules crash ba...

Shake a bottle of oil and vinegar as hard as you like. Within a minute the oil has gathered itself back into one layer on top. Nothing pushed it there — no force field, no repulsion. And yet the separation is so reliable you can set your watch by it. Understanding why is the key to solubility, to soap, and to why proteins fold the way they do. The short answer: hydrophilic ("water-loving") substances are polar or charged, so they can hydrogen-bond or form ion-dipole attractions with water and dissolve in it. Hydrophobic ("water-fearing") substances are nonpolar, cannot form those attractions, and are squeezed out of water — not because water repels them, but because water molecules would much rather bond to each other. Quick comparison at a glance Feature Hydrophilic Hydrophobic Literal meaning Water-loving Water-fearing Molecular character Polar or ionic Nonpolar Can it hydrogen-bond with water? Yes No Behaviour in water Dissolves or mixes Separates out, ...

A steel paperclip is nearly eight times denser than water. Drop it in and it sinks without hesitation. Lower it flat onto a still surface and it sits there, resting in a visible dimple, apparently held up by nothing. It isn't floating in the ordinary sense — buoyancy can't support it. Something about the surface itself is doing the work. The short answer: surface tension is the tendency of a liquid's surface to shrink to the smallest possible area, caused by molecules at the surface being pulled inward by their neighbours below with nothing pulling back from above. It makes the surface behave like a stretched elastic skin, and it is measured as energy per unit area (J/m²) or equivalently force per unit length (N/m). What is actually happening at the surface Picture a single water molecule deep inside a glass of water. It is surrounded on every side by other water molecules, all hydrogen-bonding to it. The pulls come from all directions and cancel out. Net force: zero....