CH2; Electronegativity

Define electronegativity

The ability of an atom in a covalent bond to draw electrons towards it

How does electronegativity occur?

Where their is a covalent bond, the electrons are not necessarily spread evenly between them, they can be drawn more to one atom than the other, this means one atom will have a slight -ve charge with respect to the other, this is now called a POLAR molecule.

What type of molecule never experiences electronegativity?

A molecule consisting of one type of atom only- e.g.; O2, Cl2 etc They can only be covalent bonds because no electrons can be transferred.

How can you use electronegativity to predict the type of bond present?

If there is a relativly small difference in electronegativity there will only be a small attraction of the electrons to one side of the molecule, this is what happens in a covalent bond, if the difference is more significant, the atoms in the bond have a slight charge difference, this is now referred to as a POLAR COVALENT molecule where one side is electron deficient and the other has a surplus of electrons If the difference in electronegativity is large then sharing electrons is so uneven that the more electronegative element has virtually sole position of the electrons, i.e they have been transferred, however as electrons are in a state of constant motion this is hard to define. Here, the atom that loses electrons is said to be a +ve ion and the atom that gains electrons is said to be a -ve ion If both of the atoms are electropositive, i.e do not have a tendancy to draw electrons towards them then the electrons can remain delocalised and a metalic bond is created as the electrons are free to move around. Both ions in metalic bonding therefor have +ve charges

What is the trend in electronegativity?

It INCREASES ACROSS a period and DECREASES DOWN the group. It increases across a period because of increased nuclear charge as you go along but the sheilding is relatively unchanged, so the electrons will be more strongly attracted to the atom. It decreases down the group as the electrons get further away from the nucleus experiencing less nuclear attraction

What units does electronegativity have?

No units