Before you can read the parent note, you need a toolbox. Below is every symbol, term, and picture that note quietly assumes you already own. We build each one from nothing, in an order where each rung rests on the one below it.
The picture: imagine a dot in the middle (nucleus) with a haze around it (the electron cloud). See figure below — the amber dot is the nucleus, the cyan haze the electrons.
Why the topic needs it: everything about water — its shape, its charge, its bonding — is a story about where those outer electrons sit.
Picture them as the outer ring of the haze — the ones close enough to the surface to "reach out" and grab a neighbour.
The picture: in figure s02 the central O has two lines going out to H atoms (those lines are the bonded pairs) and two little "ears" of dots sticking up (the lone pairs). Look at where the four clouds point.
Why the topic needs it: the whole "why the bend is smaller than the ideal" argument (built fully in section 3) is: lone pairs push harder than bonded pairs. You cannot follow that sentence until BP and LP are two different objects in your mind.
The picture: stand at the oxygen. Look down one O–H bond, then swing your gaze to the other O–H bond. The amount you swung is the H–O–H bond angle. If water were straight (linear) that swing would be 180°; it is actually much less — noticeably bent, as figure s03 shows.
The picture: figure s03 shows the ideal 109.5° spread as faint dashed white bonds, and the real water bonds in cyan pinched inward to 104.5°.
Recall Quick check: is 104.5° closer to straight or to a right angle?
Closer to a straight line (180°) than to a right angle (90°) ::: it is a gently bent shape, not a sharp V.
See VSEPR Theory for the full method of counting pairs and reading off shapes.
Why the topic needs it: "104.5°" is meaningless unless you can see it as a specific amount of bend, know the 109.5° baseline it deviates from, and understand (via VSEPR) why lone pairs pull it inward.
The picture: the shared electron cloud slides toward oxygen. Oxygen's end goes δ− (extra electron density), each hydrogen's end goes δ+ (electron-starved). See figure s02 again — the cyan cloud is denser near O, thinner near the H's.
Why the topic needs it: δ+, δ−, μ, and "polar" are the vocabulary the parent note uses in its very first callout ("δ-O—δ+H").
The picture: in figure s04 two water molecules sit near each other; the dashed cyan line links an H of one to the O of the other. That dashed line is the hydrogen bond. Each oxygen can host up to four such links (two of its own H's reach out, two lone pairs receive).
Why the topic needs it: hydrogen bonding is the single mechanism behind ice floating, the high boiling point, and the open hexagonal lattice — all discussed in the parent note.
See also Hydrogen Bonding and Electronegativity and Polarity for the full treatment.
Why the topic needs it: "ice floats" is just "ice has lower density than liquid water." "Maximum density at 4°C" is the headline of anomalous expansion.
The picture below is a dependency ladder: an arrow "A → B" means you must understand A before B makes sense. Read it from the top down. Atoms and their electrons (top) are the raw material; the bent shape and unequal electron-pulling combine into polarity; polarity gives hydrogen bonding, which explains ice and expansion; and dissolved ions plus polarity explain water hardness. Follow any single path from top to bottom and you have a complete story.
Legend: boxes = a concept you build on this page; arrows = "needed before." The two bottom rows (G, I) are exactly the phenomena the parent note explains — everything above them is scaffolding.
