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If you bake a lot, you may have realized  that while glass cookware exists,

not all glass is okay to use in the oven.

Normal glass can actually  shatter and explode in there.

This happens because as the  glass warms up in the oven,

the molecules inside it try to expand.

But when you take that glass out and place  it on something cool, like a countertop,

then the part of the glass touching  that starts to contract instead.

And this fight between the  parts that are still expanding

and those that are contracting places  stress on the glass's internal structure.

That's a thing called thermal shock.

This stress is then released  by the whole thing shattering.

But something like your glass  brownie pan is different,

and the reason why comes down to the chemistry.  

Now, the main component in  glass is silicon dioxide.

And the glass takes the form of a network of  bridges between the silicon and oxygen atoms.

Except, pure silicon dioxide  glass is hard to manufacture

because the bonds between atoms are so strong,

and it takes a lot of heat to melt that stuff  to make glass, around 1700 degrees Celsius.

So, manufacturers add other  ingredients called fluxes

to make the glass melt at a lower temperature.

The most common extra ingredients  are sodium oxide, also known as soda,

and calcium oxide, also known as  lime, which acts as a stabilizer.

This type of glass is called,  unsurprisingly, soda-lime glass,

and it makes up about 90% of the world's glass.

But adding these extra ingredients  can also make the glass weaker

and more vulnerable to thermal shock once  everything's cooled down and solidified.

And that's especially true  of the ingredient sodium.

Some of the oxygens in the  glass' silicon-oxygen chain

end up binding to the sodium  instead of continuing the network.

Those are called non-bridging oxygens.

And having them makes the whole  structure less well-connected

and more likely to expand when heated.

Hence why you shouldn't put  a Mason jar in the oven.

But there are types of glass you can put in  the oven and take out without shattering,

particularly one kind called borosilicate  glass, which contains the element boron.

The chemical boric oxide also reduces  the temperature needed to melt glass,

compared to pure silicon dioxide.

But unlike sodium, it can form  bridging oxygens in a glass,

typically three of them making a flat triangle.

You can make glasses that use just boron  and oxygen, or boron, silicon, and oxygen.

But having both boron and sodium in the mix,

if everything's in the right proportions,  does something cool on the molecular level.

All the elements will interact in such a way

that boron will form bonds with  four oxygens as well as the sodium.

This is because the four oxygens  give the boron a negative charge,

which attracts the positively-charged sodium.

When the sodium and boron are in the  right proportions, this does two things.

First, it creates more bridges  than boron would make by itself,

increasing the network's rigidity.

Second, this leaves the sodium unable  to produce those non-binding oxygens,

since it's already tied up with the boron.

And that creates a strong and stable  network, which reduces the thermal shock

by reducing how much the glass wants  to expand when heated or cooled.

And you still get the benefit of it being easier  to manufacture than pure silicon dioxide glass.

Today, we have a huge number  of different types of glass,

thanks to chemical tricks like this.

Including ones that, yes, can go in the oven.

If you want to learn more about other clever  chemical tricks head out to Brilliant!

They have courses in science,  engineering, computer science, and math.

Their course content is curated  by math and science educators

and lifelong learners from  MIT, Caltech, Duke, and more

Go to Brilliant.org/SciShow to try  their course The Chemical Reaction,

where you'll learn all the  bits and bolts of chemistry,

from what a chemical reaction is, to how  you can predict when one will happen.

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