Why Does Electronegativity Decrease Down a Group?

[MichaelXY]

[SOLVED] Electronegativity Confusion

Homework Statement

Looking at the periodic chart and going down, the electronegativity goes down, ie Na = .9 and K = .8 From the definition electronegativity is the ability to attract electrons. So is that to say the more electronegative would actually be the more positively charged? I ask because I am getting confused with the K pump in a neuron cell. It seems as though the side that has more Na ions is more positive than the membrane side with K ions.
Could someone please help clarify?

Thanks

Homework Equations

The Attempt at a Solution

 

[Kushal]

electronegativity is not about how much positively charged a species is. It has to do with how much shielding there is on the nucleus of the species. Electronegativity is found across covalent bonds. It is the tendency with which an atom attracts a shared pair of electron towards itself.

The greater the number of electronic orbitals and the lesser the proton number, the lesser the electronegativity of the species.

 

[MichaelXY]

So let me ask. If you had a Sodium atom on one side of a membrane, and a potassium on the other side, and were some how able to place a meter across each membrane, which side would read more positive? I am still trying to relate this to the membrane potential of a neuron.

Thanks

 

[Kushal]

i've not yet done membrane potential for neurones... but from a physics point of view, and i am assuming you are talking about sodium and potassium ions, both species have the same charge, i.e +1 or both have a proton more than electrons. the sodium ion and the potassium ion have the same charge.

 

[MichaelXY]

Ok, I think I got my answer. On one side of the membrane are K+ ions, the other side is Na+ ions. A potassium channel allows K+ ions to move freely between the membranes, until equillibrium of K+, so one side has more +1 ions than the other side, resulting in a net potential of -70 mv.