Chemistry Regents Practice Test

What would you expect to happen to the electronegativity of an element as it moves across a period in the periodic table?

1. It increases

2. It decreases

3. It remains constant

4. It fluctuates

The correct answer is: It increases

As elements move across a period in the periodic table from left to right, the electronegativity generally increases. This trend occurs because the atomic number, which corresponds to the number of protons in the nucleus, increases. As protons are added, the positive charge of the nucleus increases, which attracts the bonding electrons more strongly. Consequently, atoms become more efficient at attracting electrons, leading to higher electronegativity values. Moreover, the increasing nuclear charge is not significantly shielded by the inner electrons when moving across a period, allowing the effective nuclear charge to be felt more strongly by the valence electrons. This is in contrast to the trend seen when moving down a group, where increased electron shielding and distance from the nucleus generally lead to decreased electronegativity. Thus, the observation that electronegativity increases across a period reflects the underlying atomic structure and the tendency of atoms to attract bonding electrons more effectively as they possess more protons in their nucleus.