Question

What is electropositivity and electronegativity? Between group 1 and group 17, which is electropositive and electronegative?

Answer 1

Electronegativity is the ability of an atom to attract electrons to itself. It's governed by nucleus size (more protons - more pull!) but also the number of valence shells (farther away an electron is, less of a pull). Electropositivity is the opposte - it's the measure of an atom's ability to give up electrons.

Check out this chart which gives some electronegativity values: http://chemwiki.ucdavis.edu/ @api/deki/files/4756/=electronegativity_chart.png

You'll see that as you go from Group 1 to Group 17, there is an increase in electronegativity, resulting from the addition of protons. You'll also notice as you go down a column, you see a decrease in electronegativity values, due to the greater number of valence shells. Electrons in the inner shells "shield" the valence electrons from the attraction of the nucleus.

As the above chart also shows, electronegativity and electropostivity are really gradients - we generally associate elements on the right as being enegative and those on the left as being epositive. That's why you have compounds such as NaCl - the epositive sodium atom becomes ionized (Na+) and 'donates' its electron to the enegative chlorine, which becomes Cl-. Oh and - your noble gases, being inert, exhibit no/very little attraction towards electrons (which is why they have no numbers in the above scale)