How come 1 mole consists of 6.023 x 10^23 particles?

Answer

Hi Wesley

It is not an assumption, rather an agreement.
Individual atoms are so light that you cannot weigh them individually, at least not with the balances we know now.
That is why it is easier to work with quantities that you can weigh, and a mole has become a quantity of particles.
You can compare this to a dozen (12) or a gross (144).

In chemistry we like to use moles because in reactions there are constant ratios between the number of particles, the atoms that react.
You can compare this with making a sandwich, for example, for which you always need one sandwich, a slice of cheese, three pieces of tomato and five pieces of cucumber.
Because a sandwich is much bigger than a tomato, it is easier to work this way than to mix 100 g and 100 g together. If you took 1 kg of each ingredient you would have a lot of surplus.

You will of course find more information about this in many chemistry textbooks, but also on the internet, including Wikipedia. Also interesting is the link that is given (a mini course about mole)

I hope this gives you enough information.

regards