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Also, what is the definition of polar in this case? (9th Grade)

Does it have to do with the bonds it makes?

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  • $\begingroup$ I recommend posting this on Chemistry. Here on Biology it is just a bit out of place and that's why we put it on hold. It's an interesting question for sure. Good luck! And a pretty darn smart question for a 14-year-old. At your age, I was pondering other questions - like, what star wars figurine to buy next and stuff :) $\endgroup$ – AliceD Jan 19 '15 at 14:19
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    $\begingroup$ Thank you for your advice! Haha, and of course a 14 yr old wouldn't be a 14 yr old without games right? I'm a gamer lol. $\endgroup$ – Registered User Jan 20 '15 at 1:49
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Polar means there's a higher density of electron on the oxygen and a lower density of electrons on the hydrogens. This has to do with the electronegativity of the elements in question. Hydrogen is in group 1 which likes to lose it's electron and oxygen in group 16 which likes to get two electrons (in this case one from each hydrogen) in order to complete the octet in it's valence shell.

Also it has to do with the shape, water molecules are not linear, but rather bent in a 'v' shape. the two sides are positively charged and the middle is negatively charged. if it were linear then the middle wouldn't matter, but because it is bent, on side has a negative charge and the other side has positive charge. It's not an negative/positive change the way it is in an ion, just a slight negative/positive charge.

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  • $\begingroup$ Basically this means it has a hydogen bond? $\endgroup$ – Registered User Jan 19 '15 at 3:13
  • $\begingroup$ 1) hydrogen bonds are intermolecular, as in they occur between different water molecules that are interacting. the bond between hydrogen and oxygen is covalent. $\endgroup$ – Jasand Pruski Jan 19 '15 at 3:35
  • $\begingroup$ 2) not all molecules that are polar and have dipoles are examples of hydrogen bonds... hydrogen bonds are a special case... hydrogen bond is when Hydrogen is covalently bonded to nitrogen, oxygen or fluorine, and this slightly positively charged hydrogen comes in contact with a negative dipole on some adjacent (neighboring) molecule... $\endgroup$ – Jasand Pruski Jan 19 '15 at 3:39
  • $\begingroup$ @JasandPruski A molecule is polar when there is a net non-zero dipole moment. So asymmetric charge density though a factor, is not sufficient. You have alluded to this point when you mention linear molecule but note that canceling of dipole moments doesn't require the molecule to be linear; for e.g. CCl₄. DM is a vector and it follows the principles of vector addition. $\endgroup$ – WYSIWYG Jan 20 '15 at 5:07
  • $\begingroup$ yes of coarse, I merely narrowed it down to linearity on the case of the water molecule, because the molecular formula could indicate linearity if you didn't know the actual shape of the water molecule... $\endgroup$ – Jasand Pruski Jan 20 '15 at 20:40
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Polar simply means the electron density is not distributed evenly across a molecule. In water this is caused by the comparatively higher electronegativity of the Oxygen (you can think of this like Oxygen wants the electrons it shares in the covalent bond a lot more than the Hydrogen does so it keeps them closer but this is an oversimplification). This translates to the Oxygen having a partial negative charge (higher electron density) and the Hydrogen being slightly positive (lower electron density). The individual water molecules will form Hydrogen bonds between each other, with the positive Hydrogen of one molecule forming a weak bond with the negative Oxygen of another molecule. A molecule being polar has an effect on many of physical and chemical properties of the molecule. http://en.wikipedia.org/wiki/Electronegativity http://en.wikipedia.org/wiki/Hydrogen_bond

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  • $\begingroup$ Polar simply means the electron density is not distributed evenly across a molecule... Not completely correct. Polar means when there is a net non-zero dipole moment. $\endgroup$ – WYSIWYG Jan 20 '15 at 5:02

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