Final answer:
Electronegativity is a measure of an atom's ability to attract bonding electrons, with values generally increasing across periods and decreasing down groups on the periodic table. This property differs from electron affinity, and is influenced by the effective nuclear charge and atomic radius. Metals often have lower electronegativities due to having fewer valence electrons and larger atomic radii.
Step-by-step explanation:
Electronegativity can be defined as the measure of the tendency of an atom to attract a bonding pair of electrons. When considering electronegativity trends across the periodic table, we generally observe that electronegativity increases from left to right across periods and decreases down groups. This means that nonmetals, which are located in the upper right of the periodic table, often have higher electronegativities compared to metals found towards the lower left of the table. The element fluorine has the highest electronegativity of all, with a value of 4.0.
The reason for differing electronegativities among elements is primarily due to the effective nuclear charge (the net positive charge experienced by electrons), which increases from left to right across a period, and the atomic radius, which decreases across a period thus making it easier for the nucleus to attract bonding electrons. Conversely, as you go down a group, the atomic radius increases, causing the effective nuclear charge felt by the valence electrons to decrease, and so these electrons are less strongly attracted by the nucleus, resulting in lower electronegativity values.
Metals generally have lower electronegativity values because they have fewer valence electrons and a larger atomic radius compared to nonmetals. As such, the valence electrons are more easily lost than gained, which is opposite to the behavior of nonmetals.
Electronegativity differs from electron affinity, which is the energy change that occurs when an atom gains an electron. While both properties measure an atom's tendency to attract electrons, electronegativity is a measure of an atom's ability to attract electrons in a bond, whereas electron affinity is a measure of its ability to attract electrons to form an ion.