Problem 13 - Chemistry: The Central Science

Question

(a) What is meant by the term effective nuclear charge? (b) How does the effective nuclear charge experienced by the valence electrons of an atom vary going from left to right across a period of the periodic table?

Step-by-Step Solution

Answer

(a) Effective nuclear charge refers to the net positive charge experienced by an electron in an atom, determined by the difference between the number of protons in the nucleus and the shielding effect of lower-energy orbitals' electrons. (b) As we move from left to right across a period in the periodic table, the effective nuclear charge experienced by the valence electrons increases due to the increasing number of protons in the nucleus and a relatively constant shielding effect.

Step 1: (Explanation of Effective Nuclear Charge)

(Effective nuclear charge refers to the net positive charge experienced by an electron in an atom. It is determined by the difference between the number of protons in the nucleus (which defines the nuclear charge) and the shielding effect of electrons between the nucleus and the electron in question. The shielding effect occurs because electrons in lower-energy orbitals create a repulsive force that shields the outer electrons from the full pull of the nucleus.)

Step 2: (Variation of Effective Nuclear Charge across a Period)

(As we move from left to right across a period in the periodic table, the effective nuclear charge experienced by the valence electrons increases. This is because the number of protons in the nucleus increases, resulting in a higher nuclear charge overall. Additionally, as we move across a period, electrons are added to the same energy level, thus the shielding effect remains relatively constant. Consequently, electrons experience a stronger net positive charge, or a greater effective nuclear charge, as we move from left to right across a period.)

Step 3: (Summary)

(In summary, effective nuclear charge is the net positive charge experienced by an electron in an atom, which is influenced by the number of protons in the nucleus and the shielding effect of other electrons. When moving from left to right across a period in the periodic table, the effective nuclear charge experienced by the valence electrons increases due to the increasing nuclear charge and a relatively constant shielding effect.)