Periodicity refers to the repeating patterns in the properties of elements as you move across or down the periodic table. These trends are primarily driven by:
The Golden Rule: The increase in Z_eff across a period is the single most important factor driving nearly all left-to-right periodic trends.
Definition: The distance from the nucleus to the outermost electron shell.
Definition: The radius of an atom after it has gained or lost electrons.
Definition: The minimum energy required to remove an electron from a neutral gaseous atom. (Energy is absorbed/required).
Definition: The energy change when a gaseous atom gains an electron. (Usually exothermic/negative).
Definition: The ability of an atom within a chemical bond to attract shared electrons toward itself. (Fluorine is the highest at 4.0).
| Periodic Property | Across a Period (→) | Down a Group (↓) |
|---|---|---|
| Effective Nuclear Charge (Z_eff) | ↑ | ≈ / ↑ |
| Atomic/Ionic Radius | ↓ | ↑ |
| Ionization Energy | ↑ | ↓ |
| Electron Affinity | ↑ (More -) | ↓ (Less -) |
| Electronegativity | ↑ | ↓ |
| Metallic Character | ↓ | ↑ |
| Non-Metallic Character | ↑ | ↓ |
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Periodic Trends & Periodicity: Notes & Examples PDF is a fundamental concept in inorganic chemistry. Understanding the mechanisms, reaction conditions, and stereo-chemical outcomes is crucial for mastering organic chemistry. Our curated resources provide step-by-step visualizations to help you excel.
SELF TEST
Which element has the highest electronegativity on the periodic table?
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As you move across a period, protons are added to the nucleus while electrons are added to the same valence shell. The increased effective nuclear charge (Z_eff) pulls the electron cloud closer to the nucleus, reducing the radius.
Effective nuclear charge is the net positive charge experienced by valence electrons. It is the actual nuclear charge (number of protons) minus the shielding effect caused by inner-shell electrons.
Cations lose their outermost electron shell and experience reduced electron-electron repulsion. With fewer electrons but the same number of protons, the remaining electrons are pulled tighter to the nucleus.