Negative ions

[Moontanman]

How are negative ions, ie negatively charged atoms formed?

[Karnuvap]

Depending on the atomic number of the atom it will have the equivalent number of electrons in the neutral atom. Around an atom the electrons arrange themselves into "Shells" and these shells have so many spaces for electons to be in. The innermost shell has space for two electrons the next one out has space for eight and so on.

 

The key piece of information to know is that these shells "prefer" to be FULL.

 

So, for example, Fluorine has atomic number 9. First shell fills with its complement of two electrons but the second shell now only has 7 whereas there are 8 spaces. Thus, it is most stable when it acquires an extra electron from somewhere (anywhere - this is pretty vile stuff) to make-up the full complement of 8 in that next shell. As soon as it does this is, it becomes a, relatively happy, negatively charged Fl- ion.

 

There are all sorts of rules about the potential numbers of electrons in each 'level' of electron shell - some levels have various sub-orbits and they fill-up in a strict order. But understanding the simple fact that shells like to be complete explains pretty much all of inorganic chemistry and quite a bit of the organic chemistry too.

 

The complement of negatively charged, is positively charged for the same reason - desire for a full shell. so Sodium has atomic number 11 which would mean full inner shell (2), full next shell (8) then one lone electron in the next shell. The desire that sodium has to get rid of this lone electron is enormous and this is why raw sodium is so reactive. It will lose this electron to anything it can so that it can make itself into an Na+ ion.

[Moontanman]

Ok, thanks, I should have just checked out my chemistry text books, Now that you have told me I do remember this from chemistry. I guess I was thinking about it from an odd perspective, If an atom is neutral I can see how an electron could be knocked off but it seemed odd from that stand point how an neutral atom could hold on to an extra electron. Senility creeping in I guess.

[gregdevid]

Hi,

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Model of Bohr this will be from or in the outer shield 'n'. A negatively charged ion, which has more electrons than it has protons, is known as an anion (ἀνά ana: Greek 'up') (pronounced /ˈænaɪən/; an-eye-on). Conversely, a positively-charged ion, which has fewer electrons than protons, is known as a cation.