To read the parent note you must already own a handful of small ideas. Below, each one gets: what it means in plain words → the picture it draws → why the topic can't work without it. They are ordered so every new word is built only from words already defined.
Not all electrons matter for shape. Only the outermost ones — the valence electrons — take part in bonding.
Picture: imagine a dartboard. The nucleus is the bullseye; valence electrons are darts stuck in the outer ring — those are the only darts we can rearrange.
Why the topic needs it: the whole recipe starts by counting V. If you don't know what V means, the line "O has V=6" is gibberish.
Why the topic needs it: "lone pair" appears in every table, every angle, every example. The parent's ordering LP–LP>LP–BP>BP–BP is meaningless without this fat-vs-thin picture.
Picture: stand at the central atom, point one arm down each bond — the gap between your arms is the bond angle.
Why the topic needs it: the parent's punchline is a set of numbers — 109.5°→107°→104.5°. Without knowing what a degree measures, those numbers say nothing.
This is the seed idea of VSEPR Theory — the framework the whole parent note lives inside.
Why the topic needs it: this is the engine. "Spread to maximise distance = tetrahedron" only makes sense once you accept domains push each other apart.
Why the topic needs it: every worked example opens with "SN = ...". It is the address you look up in the geometry table. See Steric number and molecular shape for the full generalisation.
Test yourself — cover the right side and answer out loud.
What are valence electrons, and what is V for oxygen?
The outer-shell electrons an atom brings to bonding; oxygen has V=6.
Why do electrons travel in pairs, not singly?
Two opposite-spin electrons can share one region of space stably; a single electron seeks a partner — so the basic clump is a pair.
What is the difference between a bond and a lone pair?
A bond is a pair shared between two nuclei (thin, stretched); a lone pair is a pair held by one nucleus (fat, bulging).
How many electron domains is a double bond?
One — all bonds to the same neighbour point in one direction, so it is a single (fatter) domain.
What does a bond angle measure and in what units?
The opening between two bonds meeting at the central atom, measured in degrees.
State the repulsion principle in one sentence.
All electron domains repel, so they settle as far apart as possible around the central atom.
Write the formula for steric number.
SN = (atoms bonded) + (lone pairs on the central atom).
What is the difference between electron geometry and molecular shape?
Electron geometry uses all domains (bonds + lone pairs); molecular shape uses only the atoms, ignoring lone-pair positions.
Why does a lone pair push harder than a bonding pair?
It is held by one nucleus so its cloud is fatter and closer in, occupying more angular space.
Recall One-line summary of D1
Count clumps of electrons (domains), let them repel to spread out, then hide the lone-pair clumps to name the shape — that's the whole game the parent note plays.
