Why do two atoms of hydrogen and one of oxygen make water?

Question

Thank you!

Answer 1

What we call water is made up of molecules each containing 2 hydrogen atoms and one oxygen atom.

If the numbers were different, it wouldn't be water, it would be something else.

I am not sure I really get your question, though.

It seems to me that you could say water is defined as being H2O, or chemistry is defined such that water is H2O.

Now if you mean to ask why is the ratio 2:1, that gets more complex

Answer 2

Electrostatic "comfort"!

O has 6 e's in its valence shell and needs 2 or the "equivalent" of 2 more to complete its octet.

H has 1 and need 1 more to complete its "duet"

So 2 H's combine with 1 O. THe nature of that combination is what the modelers have provided. Thus in the spdf model, atoms form bonds between them that have 2, 4, or 6 electrons (single, double, triple bonds). This allows each atom to achieve its shell completion - by sharing.

In the MCAS model, the line-of-sight between two atoms does NOT contain electrons. In this model, H's turn their unprotected region towards the unprotected region of the O, much like water buffaloes would do when under attack. Thus, each atom guards the others back!