What is green house gases?
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What is green house gases?

[From: Chemistry] [author: ] [Date: 01-07] [Hit: ]
What is green house gases?......

What is green house gases?


oyubir say: It is mainly gases made of either several distinct atoms, or made of identical atoms, but at least 3 of thems.

When sun ray hit the atmosphere, some photons are diffused (the blue ones), some other reach directly the ground. Hence the reason why the sky appear blue. I am sure you have already read this. It is almost unrelated. But I mention it, because it is slightly the same thing that will happen on the way back.

Once the rays reached the ground, depending on the color of the ground, either they simply go back. For example, if the ground is snow, the light is almost unchanged and diffused back upward - in all directions, but that means back to space, mostly.

But if the ground is darker, it is turned into heat, and therefore infrared rays.
Those infrareds rays are also diffused, back to space.

Unless, something happen to them before to make them go back again to the ground.

And that thing is that they may encounter greenhouse gas particle.
What infrared rays do to a molecule is that it "shake" the atoms in it. Not enough to break it (that would be what ionising rays do). The wavelength is not small enough to shake the nucleus inside its electrons cloud neither. Hence the reason why simple monoatomic molecule are not impacted (see later).

And sometimes, depending on the form of the molecule, moving atoms creates a change in the relative position of the barycenter of positive and negative charges. And this change create a wave, that is photons of infrared rays. So photons of IR might be absorbed by the molecule, that emits then another photon. But not in the same direction. That new photon might head back to earth.

So part of the infrared that should have went back to space, stay on earth. Thus changing the equilibrium between incoming and outgoing energy, and therefore the equilibrium temperature. Earth is slightly warmer than a planet of its color and its distance from the Sun should be.

As for why some gases do that, and some other don't. As I said is a matter of creating a variation in the relative position of the negative and positive charges by moving a whole atom (moving the atom AND its electron cloud).

For a monoatomic molecule, moving the atom changes nothing to the relative position of negative and positive charges. You move the whole thing.

For a diatomic "pure" molecule (made of twice the same atom, like O2 or H2), moving one atom just stretch the molecule. But again, change nothing to its polarization (polarization: difference between barycenter of positive and negative charges).
Whether the molecule is O==O or temporarily O=====O, it changes nothings to the absence of polarization.
The molecule is always perfectly symmetric, however you stretch it. So no polarization is possible (a symmetric molecule is not polarized. All direction are identical)

For diatomic molecule not made of twice the same atom, like CO, its different. There you have no symetry. So unless the molecule is one where chance make the barycenter of positive and negative charge be exactly at the same point, you have polarization. And when you move one of the atom, you change this disymetry.

For triatomic molecule, even made of three times the same atom, like O3, same thing. There is a polarization. And moving an atom change that polarization.
Even if the molecule is not polarized by default, like CH4, which is perfectly symetric, if you move one of the atoms, it ceases to be symetric. So there is a variation of the polarisation (it was 0, and ceases to be 0 if you move an atom).

So, conclusion is that green house gases are gases whose atom configuration is such as moving an atom inside it will make the polarization vary. And that, for this reason, prevent a part of the IR from the earth, that was supposed to go back in space, to leave.
Those gases are (mainly) those made of either more than 2 atoms, or made of 2 different atoms.
Hence the reason why O2, H2, N2, ... are not green house gases. While CO2, H2O, CH4, CO, O3, ... are.
Zirp say: greenhouse is one word.

it's gases that visible light can pass through, but infrared can't
poldi2 say: Green house gases ARE gases that allow light to enter but stop infrared radiation (heat) from leaving.
pisgahchemist say: The "greenhouse" effect.....

Greenhouse gases are any gases in the atmosphere which absorb infrared energy and re-radiate it. Notable greenhouse gases are water vapor, methane and carbon dioxide.

The "greenhouse" effect is actually a misnomer. What keeps the Earth warm isn't the same as how a greenhouse works. A greenhouse works by trapping heated air. On Earth there is nothing to trap hot air. Electromagnetic energy from the sun is transmitted through the atmosphere, hits surface, is absorbed and warms the surface. The energy radiates back into space except for some which is absorbed by compounds in the atmosphere and re-radiated. Some of the re-radiated energy is directed back toward the surface, helping to warm it. Water vapor is the most prevalent re-radiator in the atmosphere, followed by some other gases including methane and carbon dioxide. But when there are too many of these re-radiating molecules in the atmosphere, the surface temperatures rise, with potentially catastrophic results.

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