van der Waals bond
/ van der VAHLS bond /
Even atoms that have no charge to share and no electrons to trade still feel a faint, fleeting tug toward one another. Think of two perfectly balanced spinning tops that, just by wobbling at the same moment, gently nudge each other. The van der Waals bond is this whisper-soft attraction between neutral atoms or molecules that have no other reason to stick together.
The mechanism is subtle but real: the electrons in any atom are always in motion, so at any instant the cloud is slightly lopsided, giving the atom a tiny, momentary positive-and-negative split called a dipole. That fleeting dipole tugs on a neighbor's electrons, coaxing it to lean the opposite way, and the two flickering dipoles attract. Averaged over time the effect is always attractive but extremely weak, and it fades quickly with distance, so it only matters when atoms are nearly touching.
Van der Waals bonding matters because it is the only thing holding together substances with no stronger options — frozen noble gases, waxes, and the stacked sheets of graphite and other layered materials. It is also the grip a gecko's foot uses to climb glass. The honest caveat is its weakness: van der Waals bonds are tens to hundreds of times feebler than covalent or ionic ones, which is why such solids are soft, slippery, and melt at very low temperatures.
A pencil works because graphite is built from strong, flat sheets of carbon stacked like pages, held to each other only by weak van der Waals attraction. When you drag the pencil across paper, those feeble inter-sheet bonds give way and whole sheets slide off to leave a gray mark.
Graphite writes because weak van der Waals bonds let its carbon sheets slide off.
Van der Waals attraction is universal — it acts between all atoms and molecules, even ones already joined by strong bonds. It is just usually drowned out, becoming noticeable only when no stronger bonding is present.