Practice: What is the identity of an element when the effective nuclear charge of its valence electrons is 18 while its shielding constant is 5?

**Effective Nuclear Charge (Z _{eff})** measures the force exerted onto an electron by the nucleus.

Concept #1: Periodic Trend: Effective Nuclear Charge

*Higher* the **Effective Nuclear Charge (Z _{Eff})**,

*Higher* the **Shielding Constant (S)**, *greater* the repulsive force between valence and inner core electrons, which results in valence electrons pushed away from the nucleus.

Concept #2: Periodic Trends

Moving towards the top right corner of the Periodic Table causes effective nuclear charge to increase.

Example #1: Which of the following represents a chalcogen with the greatest effective nuclear charge?

Concept #3: Calculate without Slater’s Rules

Example #2: What is the effective nuclear charge felt by an electron in the third shell of an aluminum atom?

Practice: What is the identity of an element when the effective nuclear charge of its valence electrons is 18 while its shielding constant is 5?

Example #3: Using Slater’s Rules, calculate the effective nuclear charge of a 3p orbital electron in calcium.

Practice: In which orbital does an electron in a sulfur atom experience the greatest shielding?

Practice: Rank the following elements by effective nuclear charge, Z_{Eff,} for a valence electron: Kr, Se, Ca, K, Ge

Practice: Using Slater’s Rules calculate the effective nuclear charge of the 4d orbital electron in iodine.