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SIMZZ

What is polarity? and how is it applied to ionic and covalent bonds/

Polar bonds are where one atom has a higher electronegativity (attraction to electrons) than the other, so the electrons are unevenly distributed resulting in a positive side and a negative side, ie polar.

Reply 161

SIMZZ

calumc

Polar bonds are where one atom has a higher electronegativity (attraction to electrons) than the other, so the electrons are unevenly distributed resulting in a positive side and a negative side, ie polar.

THANKS

Reply 162

Sahir

2

calumc

Polar bonds are where one atom has a higher electronegativity (attraction to electrons) than the other, so the electrons are unevenly distributed resulting in a positive side and a negative side, ie polar.

Yeah that would give you a BOND dipole in a covalent compound, which sometimes results in a molecular dipole. However in a compound like CCl4 (draw the tetrahedral shape), the molecule is overal non-polar as all the dipoles cancel.

With reference to ionic bonds, you get "polarisation" when the difference in electronegativity between the two species involved is not extremely large... for example in Cs+F- you get quite quite a pure ionic bond (the ions are almost spherical), but in MgCl2, the electric field around the small cation Mg+ distorts the electron shells around the large anions Cl- .. hence the ions are not spherical but the Cl- ions look like they "point" towards the Mg+ ions.

Reply 163

FidoDiDo

SIMZZ

What is polarity? and how is it applied to ionic and covalent bonds/

Polarity is caused when the Centre of positive charge do not coincide with the centre of Negative charge, so there will be an un-equal distribution of charge throughout the molecule.This will possess a Dipole in the molecule.This usually occours when 2 non-metallic elements with difference in Electronegativity are bonded together.As u know electronegativity is the ability of a bonded atom in a molecules to attrack electrons.So the more electronegative Atom will withdraw the bonded electron cloud towards it, so their will be an un-equal distribution of charge.The side where there is more electrons than the other will have a Partial Negative charge [ side of more electronegitive atom ] and the other side will have a Partial positive Charge.
and Example is H-F.
if a covalently bonded atoms have difference in electronegativity, they will possess a dipole .. this will cause the rise of a special type of intermolecular forces of attraction known as Permenant Dipole-Dipole interaction, which is stronger than Normal Van der waal forces [found in non-polar molecule].The presence of polar molecule Confers Partial ionic character in a convalent compound.The higher the difference in electronegativity the higher the polarity and the stronger the forces of attraction between adjacent molecules.So this will increase the precentage of ionic character on Covalent compound!Becuz as u kno ionic Bonds are stronger than covalent ones.

So non-polar molecules made up of atoms with same electronegativity, as the electronegativity starts to differ this will causes the increase in percentage of ionic character in a covelently bonded atoms.On pauli scale if the difference in electronegativity exceeded 4 [ Very big diffrence in electronegativity ] then the atoms would be really bonded ionically instead of Covalenetly
So the Factor affect the presence of partial ionic character on Covalent compound is the diffrence in electronegativity!

For ionic bonds .. if the cation has a high charge density [ ratio of size to nuclear charge ] then it will really distort the electron cloud on the anion its bonded too .. this will usually bring the electrons between the 2 atoms, just like as if the atoms are sharing these electrons, then in this case this will Confer a partial covalent character on ionic compounds.this is why AlCl3 has a very low Melting point .. this is due to the high charge density of Alumnium and large ionic radius of Cloride ion ..which encourage polarization.If the anion was small then it holds its electron cloud more firmly, so its more difficult to polarise.AlF3 is pure ionic has a very high Melting point about 2273 K.Polarization doesnt occour becuz F- is small to be polarised.
so the 2 factors affect the polarization in ionic compound are;
Charge density of cation
Size of anion

Hope i helped :s-smilie:

Reply 164

FidoDiDo

This graph should explain for covalent compounds!
it says : Percentage of ionic character against difference in electronegativity

A quick one this, but I'm stuck.
Gallium has 2 isotopes:
69
Ga
31
and
71
Ga
31

The RAM of a gallium sample is 69.8g/mol
Claculate thae % ambundance of the 69 istope in the sample
TIA :smile:

Reply 166

FidoDiDo

InterCity125

A quick one this, but I'm stuck.
Gallium has 2 isotopes:
69
Ga
31
and
71
Ga
31

The RAM of a gallium sample is 69.8g/mol
Claculate thae % ambundance of the 69 istope in the sample
TIA :smile:

its 60

Reply 167

InterCity125

1

FidoDiDo

its 60

What method did you use?

Reply 168

A0307

7

InterCity125

What method did you use?

I would think of it as:

69x + 71(1-x) = 69.8

(where x is the fraction of 69 isotope)

so:

69x + 71 - 71x = 69.8

2x = 1.2

x = 0.6

Reply 169

FidoDiDo

its a horrible quesion .. cuz u got to use maths :tongue:

the way is :
(69 x a) + (71 x b) = 69.8
-------------------
100

so (0.69 x a ) + (0.71 x b) = 69.8
and a + b = 100
SO
(a + b=100) x either 0.69 or 0.71 ....... i ll use 0.69
= 0.69a + 0.69b = 69

So (0.69 x a ) + (0.71 x b) = 69.8
Minus(-) 0.69a + 0.69b = 69
equal 0.02b = 0.8
1b = 40

AT LAST .... b = 40%
So a got to be 60%

Reply 170

InterCity125

1

Thanks FidoDiDo. It was only worth 2 marks! Very clear method - cheers.

AnytimeZ

uimm sorry so back to the electrophiles and neuclophiles.. someone earlier methioned that electrophile have 6 electrons on outer shell and neucleophile has 8? what about OH- it only has 7 but it's neucleophile