Chemistery

Both numbers sit on the same atom in the same molecule, and both look like charges. Yet carbon in CO has a formal charge of −1 and an oxidation number of +2 — opposite signs on the same atom. That isn't a contradiction. They're answers to two different questions, and each one is deliberately, usefully wrong in its own way. The short answer: formal charge splits every bonding pair straight down the middle, giving one electron to each atom, and asks what charge each atom would then carry. Oxidation number does the opposite extreme — it gives both electrons of every bond to the more electronegative atom. Formal charge is for picking the best Lewis structure; oxidation number is for tracking redox. Quick comparison at a glance Feature Formal charge Oxidation number How bonds are split Evenly — one electron each Entirely to the more electronegative atom Assumption made Bonds are perfectly covalent Bonds are perfectly ionic Electronegativity used? No Yes — it decides who ta...

Carbon's outer shell holds one 2s orbital and three 2p orbitals — four orbitals of two different shapes and energies. So why are all four C–H bonds in methane identical, the same length and the same strength, pointing at perfect 109.5° angles? Something must be evening them out. That something is hybridization. The short answer: hybridization is the mixing of an atom's valence s and p orbitals into a new set of identical hybrid orbitals that point in the directions the bonds actually need. Mix one s with one p and you get two sp orbitals; one s with two p gives three sp² ; one s with three p gives four sp³ . What hybridization actually means Take methane. If carbon bonded using its raw orbitals, you'd expect three bonds at 90° from the three p orbitals and one different bond from the s orbital. Real methane has four identical bonds at 109.5°. The atomic orbitals plainly aren't being used as they come. Hybridization is the bookkeeping that fixes this. Before bond...

Here's a question that has cost more marks than almost any other in bonding: what is the shape of water? Tetrahedral or bent? Both answers appear in textbooks, and both are right — to two different questions. Once you see which is which, you'll never lose the mark again. The short answer: electron geometry is the arrangement of all electron domains around the central atom, lone pairs included. Molecular geometry is the arrangement of the atoms only , with lone pairs left out of the name. They're identical when there are no lone pairs, and different every time there are. Quick comparison at a glance Feature Electron geometry Molecular geometry Also called Electron-domain geometry, electron-pair geometry Molecular shape, shape of the molecule What it counts Bonds and lone pairs Bonded atoms only Number of possibilities 5 (linear → octahedral) Many more — each electron geometry branches Determined by Total electron domains Domains minus lone pairs Sets the ideal ...

A Lewis structure is flat. A real molecule is not. Water isn't a straight line, methane isn't a cross, and ammonia isn't a triangle — and the theory that gets you from the flat drawing to the real three-dimensional shape, in about thirty seconds per molecule, is VSEPR. The short answer: VSEPR stands for Valence Shell Electron Pair Repulsion , and it says that the groups of electrons around a central atom push each other as far apart as possible. Count the groups, arrange them at maximum separation, and you have the molecule's shape. What VSEPR actually claims The whole theory rests on one idea: electrons repel electrons . Every region of electron density around a central atom — every bond and every lone pair — is negatively charged, so they all shove each other away. They settle into whatever arrangement puts them at the greatest possible angular distance from one another, and the atoms come along for the ride. That's it. There's no orbital mathematics inv...

You've drawn the Lewis structure. Every atom has its octet, the dots are all placed — and then the question asks for the shape, and suddenly it matters which pairs are which. Getting lone pairs and bonding pairs straight is the single step between a correct dot diagram and a correct molecular shape. The short answer: a bonding pair is a pair of electrons shared between two atoms, holding them together — it's what a line in a structural formula represents. A lone pair is a pair of electrons sitting on one atom only, bonded to nothing, and because it's held by a single nucleus it spreads out more and pushes harder on everything around it. Quick comparison at a glance Feature Bonding pair Lone pair Also called Shared pair, bond pair Non-bonding pair, unshared pair How many nuclei attract it Two One Shown in a structure as A line (or two dots between atoms) Two dots on a single atom Shape in space Pulled tight between two nuclei Fatter and closer to its own atom Rep...

You have an equilibrium. You poke it. Which way does it move? There's one rule that answers this for every disturbance you'll be asked about, and it fits in a sentence. The short answer: Le Chatelier's principle states that if a system at equilibrium is disturbed, the position of equilibrium shifts in the direction that partially opposes the change. Add something and the system consumes some of it; heat it and it absorbs some of that heat. What "opposes the change" actually means The system doesn't undo the change — it can't. It partially offsets it. Add 1 mol of a reactant and the shift will use up some of that mol, so the new equilibrium has more of it than before, just less than 1 mol more. Think of it as pushing back, not resetting. The three disturbances 1. Concentration You do this Equilibrium shifts Because Add a reactant Right (towards products) To use some of it up Remove a reactant Left To replace some of it Add a product Left To...