OCR Chemistry A/S Unit One - Atoms, Bonds and Groups

Fatema991

Hey there, I've looked around on this and there's no specific thread for this exam so I thought I'd create one! Hope everyone's okay with revision! If anyone's reading this, Can you explain what a polar molecule is? and can a molecule have 'polar bonds' but not be a polar molecule?

Fatema

A polar molecule is formed when there is an uneven distribution of electrons across a molecule (i.e. some atoms are electronegative which means that they drawing the binding electrons towards themselves, thus giving themselves a partial negative charge and the other atom in the bond a partial positive charge)

When the partially positive end of one molecule is near the partially negative end of another molecule, they attract one another (much like magnets) and the mutual attraction is known as EDIT: Van der Waal's forces (EDIT: therefore it is only possible with molecules containing polar bonds)

Hope this helps :smile:

Reply 3

Adhavan

A polar molecule is formed when there is an uneven distribution of electrons across a molecule (i.e. some atoms are electronegative which means that they drawing the binding electrons towards themselves, thus giving themselves a partial negative charge and the other atom in the bond a partial positive charge)

When the partially positive end of one molecule is near the partially negative end of another molecule, they attract one another (much like magnets) and this mutual attraction is known as a polar bond (therefore it is only possible with polar molecules)

Hope this helps :smile:

You can get polar bonds in non-polar molecules, eg, a linear molecule.

EDIT: Lol looking at your AS marks, I'm probably wrong. :p:

Hmm actually, I think what you have described as a polar bond is actually an intermolecular force.

Reply 4

PeterMcPete

1

Is this AS Salters Chemistry (new for 2009)? Cos I'm sure this doesnt come up at all.

Reply 5

DaveJ

You can get polar bonds in non-polar molecules, eg, a linear molecule.

EDIT: Lol looking at your AS marks, I'm probably wrong. :p:

Care to elaborate?

Reply 6

Toiletpaper8

13

DaveJ

You can get polar bonds in non-polar molecules, eg, a linear molecule.

EDIT: Lol looking at your AS marks, I'm probably wrong. :p:

Hmm actually, I think what you have described as a polar bond is actually an intermolecular force.

Bond polarity has nothing to do with molecular shape.

Reply 7

trance addict

Oh and a molecule can have polar bonds but not be a polar molecule when the atoms bonding to each other have a similiar electronegativity, the charges cancel each other out and the molecule has no overall charge (think of H2) so there is no delta negative/positive charge on either side of the molecule to attract and bond with other molecuels via permanent dipole-dipole forces (they can still bond via van der waals forces though)

Forgot to mention this :s-smilie:

Molecules can have an induced charge and bond via temporary dipole-induced dipole forces (although technically when a dipole is temporary/induced, the molecule is polar at that point)

Reply 8

trance addict

18

Adhavan

Forgot to mention this :s-smilie:

Molecules can have an induced charge and bond via temporary dipole-induced dipole forces (although technically when a dipole is temporary/induced, the molecule is polar at that point)

those are van der waals forces :P thats dipole induction when the two repelling forces induce a temporary dipole

Reply 9

Adhavan

Care to elaborate?

Well basically, I think in your post, what you described as a polar molecule is actually a polar bond, and what you described as a polar bond is actually an intermolecular force.

A polar bond is when for example 2 atoms bond covalently, and one is more electronegative than the other, thus the shared electrons are closer to that atom, creating one delta plus atom and one delta minus atom.

A polar molecule is whenever the delta plus and delta minus regions of the molecule do not cancel each other out, as the molecule is not symmetrical.

Tbh, I'm probably wrong.

Reply 10

trance addict

those are van der waals forces :P thats dipole induction when the two repelling forces induce a temporary dipole

lol no i meant that I forgot to mention what i quoted from you in my initial answer :p:

Reply 11

DeanK2

Adhavan

Care to elaborate?

CF(4) is a non polar molecule, as overall there is no net charge imbalance, as the vector sum of each individual delta charge that has been created is zero.

I do, however, hope it is quite clear that the C-F are polar...

Reply 12

Toiletpaper8

13

Adhavan

A polar molecule is formed when there is an uneven distribution of electrons across a molecule (i.e. some atoms are electronegative which means that they drawing the binding electrons towards themselves, thus giving themselves a partial negative charge and the other atom in the bond a partial positive charge)

When the partially positive end of one molecule is near the partially negative end of another molecule, they attract one another (much like magnets) and this mutual attraction is known as a polar bond (therefore it is only possible with polar molecules)

Hope this helps :smile:

Generally, a polar bond refers to bond polarity, i.e. a covalent bond where there is a difference in electronegativity between the two atoms involved. For example H-Cl or C=O, No?

Reply 13

DaveJ

Well basically, I think in your post, what you described as a polar molecule is actually a polar bond, and what you described as a polar bond is actually an intermolecular force.

A polar bond is when for example 2 atoms bond covalently, and one is more electronegative than the other, thus the shared electrons are closer to that atom, creating one delta plus atom and one delta minus atom.

A polar molecule is whenever the delta plus and delta minus regions of the molecule do not cancel each other out, as the molecule is not symmetrical.

Hmm, an example off the top of my head about you saying polar bonds imply a polar molecule: HCl has a polar bond, but is linear.

HCl is a polar molecule though :p:

are you sure you're not confusing yourself?

Reply 14

Toiletpaper8

Generally, a polar bond refers to bond polarity, i.e. a covalent bond where there is a difference in electronegativity between the two atoms involved. For example H-Cl or C=O, No?

yeah you're right - when i said polar bond i actually meant Van der Waal's forces :s-smilie:

Sorry about that lol

Reply 15

Adhavan

HCl is a polar molecule though :p:

are you sure you're not confusing yourself?

Yeah I removed the HCl example before your post came up, cos it was wrong. I think the rest of my post is right though; I maintain the first statement in it.

Reply 16

DeanK2

Polar Molecule: There is a net permanent charge imbalance that has occured for this molecule.

Polar Bond: Can be found in non polar molecules Cf4, Ccl4, etc), where there is no symmetry. This is due to the elctronegativity difference between the atoms within the molecule.

Reply 17

DeanK2

Polar Molecule: There is a net permanent charge imbalance that has occured for this molecule.

Polar Bond: Can be found in non polar molecules Cf4, Ccl4, etc), where there is no symmetry. This is due to the elctronegativity difference between the atoms within the molecule.

Yes that is my point. The person I quoted said (I think) that polar bonds could only occur in polar molecules.

Reply 18