Recording-2025-02-13T16:12:48.114Z

Reactivity of Elements

• Background

  • Elements in the periodic table vary in reactivity. Some elements can react violently with water.

• Trends in Reactivity

  • As you go down a column in the periodic table, atomic size increases.

  • For the alkali metals (e.g., lithium, sodium, potassium), larger atoms are more reactive.

  • Chemical properties change systematically across periods.

Atomic Size and Periodicity

• Atomic Size Trends

  • In alkali metal groups, atomic size increases going down the group (e.g., lithium < sodium < potassium).

  • Across a period, atomic size decreases as protons increase (e.g., from alkali metals to halogens).

• Periodic Properties

  • This phenomenon of repeating trends is known as periodicity, influencing the physical and chemical properties of elements.

Glass Strength and Substitution of Elements

• Glass Composition

  • Typical window glass consists of sodium, calcium, and silicon.

• Increasing Glass Strength

  • By substituting potassium for sodium, glass can become significantly stronger.

  • The larger potassium atom fills the spaces left by the smaller sodium atom, enhancing structural integrity.

• Demonstration of Strength

  • A steel ball dropped on sodium-based glass shatters it completely.

  • The same ball dropped from a greater height onto potassium-based glass shows no shattering.

Historical Context and Discoveries in Chemistry

• Dmitri Mendeleev

  • Developed the first periodic table based on atomic weight and left gaps for undiscovered elements (e.g., gallium).

  • Mendeleev predicted properties of elements that would fill these gaps, which were proven correct upon discovery.

• Glenn Seaborg

  • Rearranged the periodic table in 1944, placing actinides and lanthanides in a separate row.

  • Faced resistance but eventually gained recognition for his contributions after World War II.

• Importance of Electron Configuration

  • The placement within the modern periodic table is determined by electron configurations and energy levels.

Electron Energy Levels and Diagrams

• Understanding Electron Configuration

  • Electrons occupy energy levels, with each level having a maximum capacity.

  • The filling order follows specific rules for arranging electrons in atomic orbitals.

• Examples by Element

  • Hydrogen has a single electron in the 1s level.

  • Sodium (11 electrons): Configuration reveals layers: 2 in 1s, 2 in 2s, 6 in 2p, and 1 in 3s.

• Valence Electrons

  • The outermost electrons govern chemical reactivity and properties.

  • Groups in the periodic table share common characteristics due to similar valence electron configuration.

Impact on Scientific Understanding and Practical Applications

• X-ray Fluorescence Technique

  • Used in art analysis to determine elements in pigments.

  • X-rays knock out electrons, allowing identification of elemental signatures based on emitted x-ray patterns.

• Periodic Table Structure

  • Elements are organized in increasing atomic number (number of protons).

  • Rows are periods, and columns are groups indicating shared properties.

  • Transition metals, alkaline metals, and halogens exhibit distinct behaviors based on electron arrangement.

The Nature of Elements and Their Uses

• Element Characteristics

  • Over 70% of known elements are metals, often exhibiting high conductivity and malleability.

  • Unique properties of elements allow for various applications in daily life (e.g., calcium in milk, uranium in ceramics).

Conclusion

• Significance of the Periodic Table

  • Mendeleev's attempt to order elements without knowing about protons or atomic numbers showcases pioneering scientific thought.

  • Modern chemistry utilizes the periodic table for understanding elemental behavior and predicting properties.