What are the trends in electronegativity in halogens?

In halogens, electronegativity decreases as you move down the group from fluorine to astatine.

In the periodic table, halogens are found in Group 7 and include fluorine, chlorine, bromine, iodine, and astatine. These elements are known for their high electronegativities, which is a measure of the ability of an atom to attract a bonding pair of electrons. However, within the group, there is a trend of decreasing electronegativity as you move down the group.

Starting with fluorine at the top of the group, it has the highest electronegativity of all elements in the periodic table, with a value of 3.98 on the Pauling scale. This is because fluorine has the smallest atomic radius in the group, which means its nucleus can attract electrons more strongly.

As you move down the group to chlorine, bromine, iodine, and astatine, the atomic radius increases. This is due to the addition of electron shells. With more shells, the outer electrons are further from the nucleus and are less strongly attracted. This results in a decrease in electronegativity. For example, chlorine has an electronegativity of 3.16, bromine 2.96, iodine 2.66, and astatine has the lowest in the group with a value around 2.2.

It's also worth noting that the increase in atomic size down the group also results in an increase in shielding effect. The shielding effect refers to the reduction in effective nuclear charge on the outer shell electrons by the inner shell electrons. This further reduces the ability of the nucleus to attract the bonding pair of electrons, contributing to the decrease in electronegativity.

In summary, while halogens are generally highly electronegative, there is a clear trend of decreasing electronegativity as you move down the group from fluorine to astatine. This is primarily due to the increase in atomic radius and shielding effect.