[trickay]

Hi, I need an example of two unharmful elements (to humans), that come together to make a harmful compound (to humans).

Thanks in advance.

[xiankai]

there are plenty of dangerous compounds around. stretch your imagination abit more. the air we breath in, for example.

[Karakth]

Sounds almost like you want to make poison at home...

[trickay]

there are plenty of dangerous compounds around. stretch your imagination abit more. the air we breath in, for example.

Yeah, but the difference is I need the dangerous compound to be composed of unharmful elements.

I thought I had it with Chlorine and Sodium becoming table salt, but then I realized I was doing it backwards  .

[Borek]

So stick to C, H, N and O and check how you can kill yourself with compounds made with these elements

[Karakth]

Ok, here's what you do:

You take some innocent carbohydrate (like starch, found in foods like pasta, bread, etc) and react it in limited O₂ (some heat may be required to overcome the activation energy of the reaction) to produce polymers of benzene.

These benzene polymers can then be dispersed into the air. They are very potent carcinogens when inhaled.

[xiankai]

i doubt carbohydrates qualify as an element, though  

borek's suggestion is a great one

[Mitch]

O3

[Karakth]

Oh right he wanted elements.

Seems logical then to go with Carbon and Nitrogen, and make CN.

[Donaldson Tan]

harmless element A + harmless element B => toxic compound C

what are A, B and C?

A and B can't be nitrogen and carbon because  CN does not exist. You need a third element in the compound. eg. HCN, NaCN, KCN.

Here's some I can think of:
Carbon + Oxygen => Carbon Monoxide

But it all boils down to the criteria for what's not harmful to humans.

sulphur is harmless to touch, toxic to eat.
pure hydrogen is a fire hazard
pure oxygen is corrosive and is also a fire hazard.
liquid nitrogen gives u cold burn..

[jdurg]

Nitrogen + Oxygen => Nitric Oxide.  

[mithrilhack]

cyanides

scn

[jdurg]

cyanides

scn

SCN is actually the thiocyanide ion and really isn't that toxic or dangerous.  Plus, it must have a counter-ion to it so you'd need Fe, or Na, or K in there.