Naked Science Forum
General Discussion & Feedback => Just Chat! => Topic started by: iamjr on 21/09/2015 17:15:01
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Yes , the water cycle causes it. By why does the water cycle make rain?
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Basically the saturation point of water in air fluctuates significantly with temperature.
Water evaporates into warm air to the saturation point (forming dry steam if you will forgive approximations)
Warm air rises carrying moisture up to a higher part of the atmosphere
Air cools and the saturation point drops meaning moisture will 'condense' (or saturated steam if you will)
We now have clouds
These clouds are basically moisture rich pockets of air that if they rise any further (usually forced by land mass such as mountains), cool down any further (say during the day/night cycle) or in some cases just take on much more moisture, the moisture droplets in them will increase in number and size and eventually the buoyant forces keeping them airborne are over matched by the gravitational force and they will fall as rain.
That is HOW it makes rain.. as for why.. well it is a natural system that would theoretically operate as long as temperatures fluctuate significantly enough around the saturation curve to evaporate and condense the water.
i.e. if air temperatures get too low or too high we get no precipitation. One of the major influential factors on rainfall on earth happens to be the landscape, other factors include ocean currents, the 'jet stream' and plain old warm/cold air mixing.
Hope this helps
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Yes , it helps. But water is a polar molecule right? and the electrons that stay with oxygen most of the time? what makes water allow it to rain? the nuclear charge? the placement of electrons on the Px Py Pz ?
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Yes, water is polar, and that determines the temperature and pressure required for it to rain.
But water is not alone in constituting rain. For example, it rains sulfuric acid on Venus, methane on Titan, and I think it snows nitrogen on Pluto. Presumably there are places in the universe where it rains nitrogen or ammonia, or even carbon dioxide if the conditions are right.
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Sorry, yes Chiral has clarified that.. the polar molecule causes what is known as hydrogen bonds forming which affect the physical properties i.e the melting point, boiling point etc of the compound.
This is why water with a molecular weight of 18 (sorry was modding this when you replied) is liquid at 20degC and Propane Mw of 44 is gaseous at 25degC where as normally the lower the Mw the lower the density and boiling point
I personally doubt the 'exotic' rains on other planets.. H2SO4 and NH3 yes these are very likely, but I personally believe that there needs to be a level of distinction in polarity between the rain media and the atmosphere so that the rain media can mass in concentration significant enough to form clouds so I seriously do not 100% sign up the idea of Methane rains and nitrogen snows.. but then if i knew more I would be an astronomer :)
(rough picture shows the polarity and how it forms hydrogen bonds which are weaker bonds than covalent or ionic, but show a significant factor in the determination of physical properties.
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water has a molecular mass of 18 g/mol
In addition to having an unusually high melting and boiling point for such as light molecule, water also has one of the highest dielectric constants of a liquid (80).
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How does hydrogen and oxygen form polar bonds, and why?
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sorry my pictures is bad to explain that..
The arrangement of a water molecule presents two oxygen - hydrogen bonds at an angle of 104.5degrees..
Since the hydrogen atom has but 1 electron this means other than the area between the oxygen and hydrogen atom the whole surface area of the hydrogen nucleus is exposed with a positive charge.
Since Oxygen has 6 electrons and use only 2 of them to bond with the hydrogens this clumps the negative charges up on the other side of the oxygen atom focussing a negative charge..
This presents the water molecule with a negative side and a positive side i.e. it is polar - has a positive and negative pole.
These positive and negative charges attract much like an ionic charge (but, since these are implied charges rather than actually charged particles, much weaker)
If in doubt google presents
http://www.chem1.com/acad/sci/aboutwater.html