Periodic Table And Periodicity Notes

Introduction

The Periodic Table is a tabular arrangement of chemical elements, organized based on their atomic number, electron configurations, and recurring chemical properties. The structure of the periodic table reveals periodic trends and helps predict the properties of elements. Understanding the periodic table and periodicity is crucial for the JEE Advanced Chemistry syllabus.

The Periodic Table

Structure of the Periodic Table

The periodic table consists of rows called periods and columns called groups or families.

• Periods: There are 7 periods in the periodic table. Elements in the same period have the same number of electron shells.
• Groups: There are 18 groups in the periodic table. Elements in the same group have similar chemical properties and the same number of valence electrons.

Classification of Elements

1. s-block Elements: Groups 1 and 2, including Hydrogen.
2. p-block Elements: Groups 13 to 18.
3. d-block Elements: Transition metals, Groups 3 to 12.
4. f-block Elements: Lanthanides and Actinides, placed separately at the bottom.

Notable Groups

• Alkali Metals (Group 1): Highly reactive metals like Lithium (Li), Sodium (Na).
• Alkaline Earth Metals (Group 2): Reactive metals like Magnesium (Mg), Calcium (Ca).
• Halogens (Group 17): Highly reactive non-metals like Fluorine (F), Chlorine (Cl).
• Noble Gases (Group 18): Inert gases like Helium (He), Neon (Ne).

Special Blocks

• Transition Metals: Elements in the d-block, known for their ability to form colorful compounds.
• Inner Transition Metals: Elements in the f-block, including Lanthanides and Actinides.

Periodicity in Properties

Atomic Radius

• Definition: The distance from the nucleus to the outermost electron shell.
• Trend:
  • Decreases across a period (left to right) due to increased nuclear charge.
  • Increases down a group due to the addition of electron shells.

Ionization Energy

• Definition: The energy required to remove an electron from an atom.
• Trend:
  • Increases across a period due to increased nuclear charge.
  • Decreases down a group due to increased distance from the nucleus and electron shielding.

Electron Affinity

• Definition: The energy change when an electron is added to a neutral atom.
• Trend:
  • Generally becomes more negative across a period.
  • Becomes less negative down a group.

Electronegativity

• Definition: The ability of an atom to attract electrons in a chemical bond.
• Trend:
  • Increases across a period.
  • Decreases down a group.

Metallic and Non-Metallic Character

• Metallic Character: Tendency to lose electrons and form cations.
  • Increases down a group.
  • Decreases across a period.
• Non-Metallic Character: Tendency to gain electrons and form anions.
  • Decreases down a group.
  • Increases across a period.

Deep Concepts

Effective Nuclear Charge ($Z_{\text{eff}}$)

• Definition: The net positive charge experienced by valence electrons.
• Formula: $Z_{\text{eff}} = Z - S$, where $Z$ is the atomic number and $S$ is the shielding constant.
• Trend:
  • Increases across a period.
  • Slightly increases down a group.

Shielding Effect

• Definition: The reduction in the effective nuclear charge on the electron cloud, due to a difference in the attraction forces between electrons in the inner shells and the nucleus.
• Trend:
  • Increases down a group.
  • Remains relatively constant across a period.

Isoelectronic Species

• Definition: Atoms and ions that have the same number of electrons.
• Example: $O^{2-}$, $F^{-}$, $Na^{+}$, and $Mg^{2+}$ all have 10 electrons.

Diagonal Relationship

• Definition: Similarities between elements of different groups and periods, typically seen in elements diagonally adjacent in the periodic table.
• Example: Lithium (Li) and Magnesium (Mg) show similar properties.

Anomalies in Periodic Trends

Irregularities in Ionization Energy

• Example: The first ionization energy of Boron (B) is lower than Beryllium (Be) despite being to the right of Be. This is due to the stability of the fully filled $2s$ orbital in Be.

Electron Affinity Exceptions

• Example: The electron affinity of Nitrogen (N) is less negative than Carbon (C) due to the half-filled stability of the $2p^3$ configuration in N.

Summary

Understanding the periodic table and periodicity is essential for mastering JEE Advanced Chemistry. It helps in predicting element behavior, understanding chemical reactions, and solving complex problems. Pay close attention to trends and exceptions, as these often appear in competitive exams.