The electronegativity of an element is a measure of the power of an atom to attract electrons when it is part of a compound: the greater the electronegativity the greater its drawing power. Am element with a low electronegativity (like the alkali metals) is said to be electropositive. The values shown are Pauling derived values, helpful for bond polarities and bond strengths. The elements with highest electronegativity are those with the highest effective nuclear charge and the smallest atomic radii. Fluorine, one of the smaller atoms, has the highest electronegativity, whilst potassium, rubidium, caesium and francium (all large atoms) the lowest.
Since the electropositive character of the elements decreases from left to right in a period, but usually increases in passing down a group, there are some striking similarities between pairs of elements in diagonal positions in the second and third periods. For example, between lithium and magnesium, and between beryllium and aluminium, or boron and silicon, etc.
