Module 5

• Johann Wolfgang Döbereiner


  German chemist who made significant contributions to the early understanding and classification of elements, laying the groundwork for the development of the periodic table
• Law of Triads


  1. Identified relationships among groups of three elements with similar chemical properties

  2. Observed that certain elements exhibited analogous characteristics when arranged in triads based on their atomic weights

  3. Identified triads such as lithium (Li), sodium (Na), and potassium (K), noting that the atomic weight of sodium was approximately the average of lithium and potassium, and these elements displayed similar chemical properties
• Dmitri Mendeleev


  Russian chemist widely recognized for his pivotal contributions to the development of the periodic table of elements
• Organizing Elements by Atomic Mass

  1. Organized known elements based on their atomic mass, systematically arranging them in a table format

  2. Recognized patterns and similarities among elements with analogous properties, laying the groundwork for the periodic classification of elements

  3. Included gaps for undiscovered elements, allowing for predictions of their properties based on their positions and relationships within the table
• Periodic Law


  States that the properties of elements are a periodic function of their atomic weights
• Mendeleev's periodic table


  • Provided a foundation for subsequent refinements and developments in the classification, organization, and understanding of elements
  • Laid essential groundwork for the modern periodic table and influenced advancements in atomic theory, chemistry, and related scientific disciplines
• Henry Moseley


  British physicist who made groundbreaking contributions to the understanding and organization of the periodic table of elements during the early 20th century
• Identification of Atomic Number

  1. Conducted experiments using X-ray spectroscopy and identified the concept of atomic number as the fundamental property for organizing elements

  2. Demonstrated that the atomic number, representing the number of protons in an atom's nucleus, determined an element's identity and properties

  3. Established a definitive method for assigning unique atomic numbers to elements, replacing the previous reliance on atomic mass as the primary organizing principle
• Revision and Organization of Periodic Table

  1. Arranged elements in ascending order based on their atomic numbers rather than atomic masses

  2. Highlighted the periodicity and trends in elemental properties, providing a more accurate and systematic framework for understanding the structure of the periodic table
• Moseley's revised periodic table

  • Emphasized the sequential arrangement of elements by atomic number, revealing inconsistencies and discrepancies in the previously accepted order based on atomic mass
  • Demonstrated consistent trends in properties such as electronegativity, ionization energy, and atomic radius, supporting and enhancing the predictive power of the periodic law
• Moseley's contributions


  • Significantly influenced advancements in atomic theory, spectroscopy, and related scientific disciplines
  • Laid essential groundwork for subsequent research, discoveries, and developments in chemistry, physics, and materials science
• Atomic Radius


  The size of an atom, decreasing across a period and increasing down a group due to changes in electron configuration and shielding effect
• Atomic radius across period 3 (Na to Cl)


  Decreases due to increasing nuclear charge and effective attraction
• Ionization Energy


  The energy required to remove an electron from an atom, increasing across a period and decreasing down a group
• Ionization energy across a period

  Increases due to stronger attraction between electrons and the nucleus
• Electronegativity


  Indicates the ability of an atom to attract electrons in a chemical bond, increasing across a period and decreasing down a group
• Fluorine (F) has the highest electronegativity value, indicating its strong attraction for electrons in chemical reactions
• Alkali Metals (Group 1)


  • Highly reactive metals with one valence electron, exhibit properties such as low density and reactivity with water
• Alkali Metals


  • Sodium (Na) and potassium (K) are alkali metals that react vigorously with water, forming alkaline solutions and releasing hydrogen gas
• Halogens (Group 17)


  • Highly reactive nonmetals with seven valence electrons, exhibit properties such as high electronegativity and reactivity with metals
• Halogens


  • Chlorine (Cl) is a halogen used in disinfectants, water purification, and chemical synthesis due to its reactivity and properties
• Noble Gases (Group 18)


  • Inert gases with complete valence electron shells, exhibit low reactivity and stable configurations
• Noble Gases


  • Helium (He) is a noble gas used in various applications, including cryogenics, balloons, and medical imaging, due to its stability and properties
• Chemical Bonding and Reactivity


  Understanding periodic trends facilitates predictions about chemical bonding, reactions, and properties of elements and compounds
• Industrial and Technological Applications

  The periodic table underpins various industries, technologies, and scientific advancements, influencing materials science, energy production, medicine, and environmental sustainability
• Transition Metals


  • Iron, copper, and titanium are essential in manufacturing, construction, electronics, and renewable energy technologies due to their unique properties and applications