What trend is observed in electronegativity across a period in the periodic table?

Electronegativity is the measure of an atom's ability to attract and hold onto electrons when forming chemical bonds. As you move across a period in the periodic table from left to right, electronegativity tends to increase. This trend can be attributed to the increasing positive charge in the nucleus of the elements as you add more protons. The greater positive charge in the nucleus pulls the electrons closer, making the atom more effective at attracting electrons.

Moreover, as the atomic number increases, the effective nuclear charge that is experienced by the outermost electrons also increases due to the reduced shielding effect from the inner electrons. This results in a stronger attraction between the nucleus and the valence electrons, thus increasing electronegativity.

As a result, elements on the right side of a period, such as fluorine and oxygen, demonstrate significantly higher electronegativity compared to those on the left side, such as sodium and magnesium. Understanding this trend is fundamental in predicting the behavior of atoms in chemical reactions and the formation of bonds.