Why does sugar make things sticky?



Why does sugar make things sticky?

In: Chemistry


Sugar molecules tend to stick together, which is what allows sugar to form cristals. When diluted in some other substance, like water or sweat, it can’t cristalize completely so it ends up making the liquid thicker, and thus sticky

Probably has something to do with intermolecular forces. That’s what determines viscosity.

I’ll pop in with another point worth knowing, although the video link is more than good enough. “Sticky” is not a universal quality. Tape, sugar, and the like is sticky on skin, on a table, on a busted muffler, whatever. However there are plenty of things these adhesives and adhesive-esque materials are not capable of bonding to. Oil your hand up and put on a band-aid: good luck. Adhesion is best considered as a two-way street. The adhesive is sticky to you, but in some physical or chemical sense (or both), if it could talk, it would say you’re sticky to it as well.

Because hydrogen likes to cling to things. In a dried state, hydrogen is in balance and you’ll notice it’s not very sticky. When in the presence of water – such as the water in your skin – the hydrogen bonds to it. It’s not just the presence of hydrogen though but how much there is in sugar, hence why water which is 2 parts hydrogen and one part oxygen isn’t “sticky” – though as you may notice it does like to cling to your skin. Sugar is 22 parts hydrogen – a lot more to stick!

So, firstly, Sugar alone doesn’t make things sticky. If it did we couldn’t have powdered or granulated sugars, they would all stick together in a solid block as soon as you put them in a bag.

What makes things sticky is a mixture of sugar and water. The water is the key part and i’ll try and explain why that is by working through a few steps.

1. Water interacts with sugar through hydrogen bonding(more below) and by absorbing hydrogens from the hydroxyl groups that are part of sugar molecules. Hydroxyl groups are a hydrogen and an oxygen, attached to carbon atoms in sugar. Getting them wet can actually create more of those hydroxyl groups.

2. Both of the above interactions serve to modify the [nuclear charge](https://en.m.wikipedia.org/wiki/Effective_nuclear_charge) of the sugar molecules. It makes it more negatively charged than it was before. Nuclear charges and dipoles are VERY complicated, but it essentially allows for something called [hydrogen bonding](https://en.m.wikipedia.org/wiki/Hydrogen_bond) to occur more easily. Don’t let the name fool you, it isn’t strictly related to hydrogen all the time, it just refers to attraction caused by nuclear charges attracting their opposite charge. Dw too much about it, but also it holds your body together and is involved in every type of chemistry that allows life to exist.

3. We feel that hydrogen bonding as stickiness because it literally is sticky. Those nuclear attractive/hydrogen bonding forces are sticky on a molecular level.

edit: sorry it’s not more ELI5, i just wanted to make sure people could go read up more if they wanted to.