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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: xiankai on June 26, 2005, 01:40:33 AM

Title: bonding
Post by: xiankai on June 26, 2005, 01:40:33 AM
im just starting to learn a few new things...

what is the difference between ionisation energy, electron affinity and electronegativity? so far i only know that ionisation energy is the energy required to form a positive ion, electron affinity is the energy required to change a negative ion into a neutral element. as for electronegativity, it is the power of an atom to attract electrons to itself.

IE = A  --> A+ + e-

EA = A- --> A + e-

EN = A + e- --> A-

at least thats what i think... can anyone further explain these terms :S
Title: Re:bonding
Post by: arnyk on June 26, 2005, 12:00:54 PM
Ionization Energy is the energy required to remove one electron from an atom.  It generally increases from left to right, and decreases from top to bottom.  

A + energy --> A+ + e-

Electron affinity is the energy released when you add an electron to an atom.  It generally increases from left to right, and decreases from top to bottom.  

A + e- --> A- + energy

Electronegativity is how strong the pull on electrons an element has when forming a compound.  In a polar covalent compound, the more electronegative element will have the partial negative charge as the electrons will spend more time near the electronegative atom.  Generally also increases from left to right and decrease from  top to bottom.  For example in a water molecule, oxygen has a higher electronegativity than that of hydrogen, therefore the oxygen has a partial negative charge while the hydrogen has a partial positive.

Of course alot of this (the general trends) will not apply to the noble gases as they are already very stable.
Title: Re:bonding
Post by: karishma on June 29, 2005, 04:02:26 PM
What is the main job of this?
I am just wondering about the formulas as well.
Title: Re:bonding
Post by: xiankai on June 30, 2005, 04:33:58 AM
what are the trends in subsequent ionisation energies and eletron affinities? what is the reasoning behind such trends? and also, what effect electronegativity has on ionic substances?

thank you for your time  8)
Title: Re:bonding
Post by: arnyk on June 30, 2005, 11:09:00 AM
You can generally tell what group an element is in by their ionization energies.

For example (fake numbers to illustrate a point here ;)):

Element X

1st I.E. = 10kJ
2nd I.E. = 67kJ
3rd I.E. = 56KJ

The first electron came off relatively easy and then the energy required jumped up dramatically.  You would conclude that this element is from group 1, since after its first I.E. it has formed its respective ion and a stable octet.  Afterwards, since it is stable now the removal of subsequent electrons is much harder.

Element Y

1st I.E. = 20kJ
2nd I.E. = 25kJ
3rd I.E. = 98kJ
4th I.E. = 110KJ

Group 2.

As for electron affinities you would use this for the elements which form anions.  Example:

Element W

1st E.A. = 5000kJ
2nd E.A. = 2kJ
3rd E.A. = 1kJ

Once again, fake numbers but it illustrates the point.  When the first electron was added a huge amount of energy was released.  After that, it quickly died down.  That means once the first electron was added, the element became its stable ion.  So you may conclude that this was a halogen.

Electronegativities can predict whether two elements form covalent, polar covalent, or ionic bonds.  Of course it is definately not a foolproof system as there are many compounds which do not comply to the numbers.  Generally though you can determine the type of bond through the electronegative difference between two elements.

Difference of >1.7 = ionic
Difference between 0.5 - 1.7 = polar
Difference between >0 - 0.5 = low polar
Difference of 0 (diatomics) = covalent.

The only one for sure would be the diatomics which are truely covalent, the rest of the "covalents" are simply very low polar or polar.  For example, sugar which does not conduct electricity in solution does not mean it is purely polar as it is not diatomic.  It is low polar.
Title: Re:bonding
Post by: xiankai on July 01, 2005, 06:06:22 AM
thank you, i learnt alot  ;)