Modern Periodic Table Overview

Modern Periodic Table

• The physical and chemical properties of elements are periodic functions of their atomic numbers.
• Elements with similar properties are arranged in vertical columns known as groups.
• Horizontal rows in the periodic table are known as periods.
• The Modern Periodic Table consists of 7 periods and 18 groups.
• Each period is characterized by its principal quantum number (n).
• The first period has two elements: Hydrogen (H) and Helium (He) — filling the 1s orbital.
• The second period contains eight elements: Lithium (Li) to Neon (Ne) — filling the 2s and 2p orbitals.
• The third period consists of eight elements: Sodium (Na) to Argon (Ar) — filling the 3s and 3p orbitals.
• The fourth period has 18 elements: Potassium (K) to Krypton (Kr) — filling the 4s, 4p, and 3d orbitals, containing 10 transition elements (Scandium (Sc) to Zinc (Zn)).
• The fifth period contains 18 elements: Rubidium (Rb) to Xenon (Xe) — filling the 5s, 5p, and 4d orbitals, containing 10 transition elements (Yttrium (Y) to Cadmium (Cd)).
• The sixth period has 32 elements: Cesium (Cs) to Radon (Rn) — filling the 6s, 5d, 6p, and 4f orbitals, containing 14 lanthanides (Lanthanum (La) to Lutetium (Lu)).

Effective Nuclear Charge (Z*)

• Effective nuclear charge increases across a period due to increasing nuclear charge with minimal shielding effect.
• Effective nuclear charge decreases down a group because the shielding effect outweighs the increasing nuclear charge.
• Slater's Rules are used to calculate effective nuclear charge:
  • Ignore electrons in higher groups (those to the right in the electronic configuration).
  • For ns and np electrons:
    • Electrons in the same group shield 0.35 (except for 1s, shielded by 0.30).
    • Electrons in the (n-1) group shield 0.85.
    • Electrons in the (n-2) or lower groups shield 1.00.
  • For nd and nf electrons:
    • Electrons in the same group shield 0.35.
    • Electrons in lower groups shield 1.00.

Ionization Energy

• Ionization energy (IE) is the energy needed to remove one electron from a gaseous atom in its ground state.
• First ionization energy refers to the removal of the first electron, second ionization energy refers to the removal of the second electron, and so on.
• General trends:
  • IE increases across a period due to the increasing nuclear charge and decreasing atomic size.
  • IE decreases down a group because of the increasing atomic size and shielding effect.
• Exceptions:
  • IE of Group 13 and Group 15 elements is lower than the preceding element due to the half-filled and completely filled valence shells in the preceding elements.
• Important note: IE has units of kJ/mol.

Electron Affinity (EA)

• Electron affinity is the energy change when an electron is added to a gaseous atom in its ground state.
• It can be positive or negative.
• Negative EA indicates energy is released during the addition of an electron, making the process exothermic.
• Positive EA indicates energy is absorbed during the addition of an electron, making the process endothermic.
• General trends:
  • EA becomes more negative (more exothermic) across a period, as the added electrons are closer to the nucleus and experience a stronger attraction.
  • EA becomes less negative (more endothermic) down a group because the added electrons are further from the nucleus and experience weaker attraction.
• Exceptions:
  • EA of Group 18 (Noble gases) is almost zero because their valence shells are completely filled, making them stable.
  • EA of Group 14 (Carbon group) is less negative due to the half-filled p orbitals.

Electronegativity

• Electronegativity (EN) is a measure of an atom's tendency to attract electrons in a covalent bond.
• It is a dimensionless quantity.
• General trends:
  • EN increases across a period due to the increasing nuclear charge and decreasing atomic size.
  • EN decreases down a group due to the increasing atomic size and shielding effect.
• Linus Pauling's scale is a widely used scale for electronegativity, with fluorine being the most electronegative element (EN = 4.0) and cesium being the least electronegative (EN = 0.8).

Polarization

• Polarization occurs due to the difference in electronegativity between cations and anions in an ionic compound.
• The electron density of the cation is attracted towards the more electronegative anion, resulting in a deformation of the anion.
• The tendency of the anion to get deformed is called polarizability.
• The ability of a cation to deform an anion is called the polarizing power.

Fajans' Rules

• Fajans' Rules predict the degree of covalent character in an ionic compound based on the cation's size and charge.
• Smaller cations with higher charges have greater polarizing power, leading to a higher degree of covalent character in the compound.

Explore the structure and significance of the Modern Periodic Table in this quiz. Learn about the arrangement of elements in groups and periods, their atomic numbers, and how they relate to physical and chemical properties. Perfect for anyone studying chemistry or looking to refresh their knowledge on this fundamental topic.