INTEC Chemistry Blog

1.6 Bonding

Posted on: July 13, 2011

1.6 has no content as yet, but feel free to leave any comments/questions

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5 Responses to "1.6 Bonding"

Mr Allan,
If you have interesting notes or want to share something, you can send an email to me…
If you have notes about our lesson Bonding, it may be useful to me because I still can’t really understand about it.
I will share it with my classmates.
my email… anaseberang94@gmail.com
Thank you.
10 EG 5 (2012)

Sir, actually I still cant get about polarization? its confused between cation and anion…

Hi. For organisational reasons, please post comments/questions into the relevant section listed on this page. https://intechemistry.wordpress.com/2012/07/10/international-education-college-page/ Thanks 🙂

Ok. Re your bonding question.

An ion is an atom (or group of atoms, in which case we can use the term molecular ion) that has gained a negative charge. E.g. Cl-, H3CHOO-, and a cation is something that has gained a positive charge (it does this by losing electrons) e.g. Na+, Ag+ etc.

The electrons in the orbitals of an anion (often called the ‘electron clouds’) are attracted to the positive charge of a cations [remember, it’s electrons that always do the moving], causing distortion of the anions electron cloud towards the cation, causing an increase in electron density between the cation and the anion. Purely ionic compounds have no shared electron density between their ions, so if the anion is polarised, there will be some electron density between those ions, and so it begins to resemble covalent bonding.

So, polarisation of anions by cation [never the other way around!], causes partial covalent character which increases the attraction between the two ionic species, hence, the bond strength is greater than the theoretical lattice enthalpy which assumes a 100% ionic model, i.e. the ionic model assumes the electric charges are fully localised on the ions and not partially shared. Hence the energy given off when ions form and then polarise is more exothermic than just ions forming.

What causes more polarisation of the anion?
a) Greater charge on the cation
b) smaller size of the cation
c) Larger size of the anion
d) greater charge on the anion

The bond strength between AgCl is greater than the bond strength between NaCl as the Ag+ ion is smaller than the Na+ ion, Ag+ and Na+ both having a singly positive charge.

Does that help?

Did it solve the problem?
Chemguide has a good couple of pages on all this.
a) http://www.chemguide.co.uk/basicorg/bonding/eneg.html
b) http://www.chemguide.co.uk/atoms/bonding/electroneg.html

Some video’s on Lattice(ionic) energy and polarisation here:
http://www.yteach.co.uk/page.php/resources/view_all?id=bond_enthalpy_dissociation_molecule_charge_resonance_energy_t&from=search (click onto page 15, and be prepared to constantly close the annoying pop-up window) and try page 16a and b.

Thank you, i can understand it.

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