Predict whether a compound of two or more elements would be covalent from the position of the elements in their periodic table or from their electronegativity values. // Predict the relative polarity of bonds based on electronegativity value. The covalency and polarity of molecules is dependant on their shape and the electronegativity of the atoms in the molecule. A bond is considered covalent or non-polar when the difference in electronegativity is lesser than 0.4. It is considered a polar covalent bond when the difference in electronegativity is between 0.5 to 1.9, and is considered ionic or polar when the difference is from 2.0 to 4.0. The definitive factor when determining on whether a molecule may be polar is if there is a distance between the positive and negative dipoles. These are the partial positive charges which are placed on an atom depending on its electronegativity in relation to the electronegativity of the atom that it is bonded too. The positioning of these dipoles in the molecule is determined by the shape of the molecule. If there are no lone pairs in a molecule, then it will have a symmetrical structure, in which case usually the dipoles will cancel out, making the molecule non-polar, or covalent. A common example of this is carbon dioxide, where the bonds are polar, however due to its linear shape, the molecule is non-polar and covalent. The most covalent molecules are actually diatomic molecules as the difference in electronegativity between the two atoms is the 0. If there are lone pairs, then the molecule is likely to be polar, due to the shape of the molecule not being symmetrical, hence there is a distance between the dipoles. An example of this is water, with 2 lone pairs, and a bent or v-shape.
