Concept

Periodic trend — where it appears

A property's systematic variation across a row or down a column of the periodic table. It is a statement about ordering that usually survives every way of measuring the property, which is why trends are safer to argue from than the values that carry them.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

$One number separates the disputed bonds from the agreed ones. Every bond in the collection, ordered by how big its electronegativity difference is as a fraction of each table's range. The six the tables disagree about are all below 0.0507; the 25 they agree about are all above 0.0584. Nothing lies between, and which elements a bond joins does not enter — a dispute is what happens when the difference is small enough that the tables' own disagreement about it is larger.$

A dispute is a small difference

Four electronegativity tables disagree about the direction of a quarter of a set of hydrogen bonds, and the interhalogens look like the natural test: five compounds with no hydrogen in them, to say whether the disagreement is about one awkward element or about the whole idea. All four tables agree about every interhalogen. They agree because the differences are large, and that is not a fact about halogens.

shape · Dipole

The gap closed when the other hundred and twenty-two pairs arrived. Every pair sorted by the size of its normalised electronegativity difference: the 31 common bonds on the left, all 153 pairs the four tables cover on the right. Filled marks are pairs the four tables put on different sides of zero. On the small set they are the 6 smallest with nothing in between; on the full set 27 uncontested pairs sit below the largest contested one.

A gap that was a choice of bonds

One number separates every disputed bond from every agreed one with nothing in between — on thirty-one bonds, which is enough to see a gap and not enough to know it is real. It is not real. The line is in the same place on all one hundred and fifty-three pairs the four tables cover, and twenty-seven agreed pairs now sit below the largest disputed one.

shape · Dipole

Named alongside it

The objects these essays reach for when they reach for this one.

Bond dipole Electronegativity Empirical scale Convention Dipole moment

All concepts