Water Question (1 Viewer)

[axwe7]

What is a polar bond? And what is a polar molecule?

In-depth explanation of both would be extremely beneficial

 

[Shuuya]

A polar bond is a bond between two elements with a vast difference in electronegativity. Electronegativity is defined as the ability of elements to attract electrons (i.e non-metals are more electronegative than metals). A polar molecule is a molecule which contains polar bonds, and is asymmetrical so that the polarity does not cancel out.

So the molecule HF is polar as the H-F bond is polar (as flourine is the most electronegative element, with a vastly greater electronegativity compared to H) and is asymetrical. In this molecule, the distribution of electrons is uneven as Flourine 'hogs' the electrons due to the higher electronegativity. So the electrons orbit closer to the nucleus of F, making it slightly negative, and thus making H slightly positive.

 

[leehuan]

Note that polar is different to 'charged', where the electron permanently orbits the other atom in an ionic bond.

Polar atoms appear in covalently bonded molecules.

 

[axwe7]

A polar bond is a bond between two elements with a vast difference in electronegativity. Electronegativity is defined as the ability of elements to attract electrons (i.e non-metals are more electronegative than metals). A polar molecule is a molecule which contains polar bonds, and is asymmetrical so that the polarity does not cancel out.

So the molecule HF is polar as the H-F bond is polar (as flourine is the most electronegative element, with a vastly greater electronegativity compared to H) and is asymetrical. In this molecule, the distribution of electrons is uneven as Flourine 'hogs' the electrons due to the higher electronegativity. So the electrons orbit closer to the nucleus of F, making it slightly negative, and thus making H slightly positive.

Polar bonds only occur in covalent networks....

However, just a few questions.. what do you mean by asymmetrical? I know that it's about the electron dot diagram, but how would you know whether a bond between two elements is asymmetrical? For example, how would you know if the dot diagram of water is asymmetrical?

Secondly, how could you judge and say that hydrogen has a vast difference between the

electronegativity

of itself and fluorine when the position of hydrogen itself on the periodic table itself is undefined? - http://chemistry.stackexchange.com/questions/4164/hydrogen-its-place-in-the-periodic-table

Thanks anyhow

 

[axwe7]

Note that polar is different to 'charged', where the electron permanently orbits the other atom in an ionic bond.

Polar atoms appear in covalently bonded molecules.

Do polar atoms appear in all covalently bonded molecules which have a vast difference in electronegativity, or is it just a prerequisite?

 

[axwe7]

bump

 

[Shuuya]

Polar bonds only occur in covalent networks....

However, just a few questions.. what do you mean by asymmetrical? I know that it's about the electron dot diagram, but how would you know whether a bond between two elements is asymmetrical? For example, how would you know if the dot diagram of water is asymmetrical?

Secondly, how could you judge and say that hydrogen has a vast difference between the of itself and fluorine when the position of hydrogen itself on the periodic table itself is undefined? - http://chemistry.stackexchange.com/questions/4164/hydrogen-its-place-in-the-periodic-table

Thanks anyhow

False, polar bonds do not only occur in covalent networks. They are found in covalent compounds in general (e.g. the O-H bonds in water are polar)

By asymetrical I mean the shape of the compound. For example, CO2 contains polar C-O bonds, but its symmetrical structure cancels out any net dipoles.

(the arrows in the diagram are vectors showing the direction of the dipole --- they cancel out when added in opposite directions)

On the other hand water is a bent molecule (due to the fact that oxygen has two lone pairs of unbonding electrons). Oxygen can form 2 bonds but has 8 electrons, and therefore covalent compounds of oxygen are generally bent. To be able to tell whether a bond is bent/linear, check to see if all the valence electrons are bonded.

The net dipole is upwards (found by adding the two vectors). The vectors do not get cancelled out due to the bent shape, and therefore water is a polar molecule.

Hydrogen can either lose an electron or gain one, it doesn't particularly care (sorry for the lame terms, I'm tired ) Compared to flourine, it only has one proton in its nucleus whilst flourine is larger and has 9 protons, and therefore flourine's nucleus is much more positive. Hydrogen's ability to attract a valence electron is therefore much lower than flourine's, as the electrons will tend towards the more positive nucleus. When comparing electronegativity, look at how many protons it has (i.e larger elements have more protons), and how many electron shells it has (the electrons become less attracted to the positive nucleus with greater distance). Flourine is the most electronegative element, whilst hydrogen is the least.

Hope that helped

 

[leehuan]

It's quite easy to assume that fluorine is the most electronegative element in the periodic table as:


a) Being in Group VII (or Group 17 if you prefer that), and basically requiring one electron to fill it's outer shell, the halogens are known for having electrons closest to the nucleus compared to all other elements in the same period (row). Even the noble gases have electrons a bit further away from the nucleus.

b) Fluorine is the lightest of the halogens. It only has two energy levels (i.e. shells). Therefore it's also more electronegative than the other halogens.

This alone distinguishes F and H by a lot as fluorine has a nucleus of 9 protons, whereas hydrogen only has 1

 

[Shuuya]

Is this preliminary chemistry?

Yes

 

[leehuan]

I swear you guys are going so ahead in the chemistry syllabus... I'm learning about valencies and how to balance chemical equations.. :/ Wut.

Sent from my GT-I9506 using Tapatalk

Keep in mind some people are either accelerated, or self learn.

Because it's only the first few weeks of school, any normal pace is still only so far into The Chemical Earth.