Chemistry: Development of the Periodic Table

Development of the Periodic Table

• Periodic table developed over time, with scientists adding elements and refining organization
• Scientists like Mendeleev organized elements by increasing atomic mass and similar properties
• Modern periodic table orders elements by increasing atomic number

Physical and Chemical Properties

• Physical properties: characteristics observed without changing the substance's composition (e.g., melting point, color)
• Chemical properties: characteristics observed when a substance undergoes a chemical change or reaction (e.g., flammability, reactivity with acids)

Pure Substances vs. Mixtures

• Pure substances have a fixed composition and properties (element or compound)
• Mixtures have variable composition and properties, made of two or more pure substances

Organization of the Periodic Table and Properties of Different Groups

• Periodic table organized into periods (rows) and groups (columns)
• Elements in the same group share similar chemical properties due to similar valence electron configurations

Dalton's Postulates

• Dalton proposed atomic theory with postulates:
  • All matter is composed of atoms
  • Atoms of the same element are identical in mass and properties
  • Atoms combine in simple whole-number ratios to form compounds
  • Atoms are neither created nor destroyed in chemical reactions

Thomson's, Rutherford's, Bohr's, and Heisenberg's Models of the Atom

• Thomson discovered the electron, proposing a "plum pudding" model
• Rutherford's gold foil experiment showed a small, dense, positive nucleus
• Bohr's model described electrons orbiting the nucleus in specific energy levels
• Heisenberg's Uncertainty Principle stated that it is impossible to know both the position and momentum of an electron precisely

Structure of the Atom

• Atoms contain protons (positive), neutrons (neutral), and electrons (negative)
• Protons and neutrons are in the nucleus, electrons orbit the nucleus in electron shells/orbitals

Calculating Average Atomic Mass of Isotopes

• Average atomic mass is calculated by considering the abundance of each isotope and its mass
• Formula: (mass of isotope 1 × % abundance) + (mass of isotope 2 × % abundance) + ...

Electron Configurations

• Electron configuration describes the arrangement of electrons in an atom's energy levels and orbitals
• Aufbau principle, Hund's rule, and Pauli exclusion principle govern electron filling

Lewis Dot Structures of Covalent and Ionic Molecules

• Lewis dot structures depict valence electrons of atoms in molecules
• Covalent bonds involve sharing electrons, ionic bonds involve transfer of electrons

Periodic Trends

• Properties of elements change predictably across periods and down groups
• Electronegativity: an element's ability to attract shared electrons in a chemical bond; higher electronegativity, stronger attraction.

Naming and Formula Writing of Compounds

• Naming and writing chemical formulas for different types of compounds (covalent, ionic, polyatomic, multivalent)

VSEPR Shapes

• Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the 3D shapes of molecules based on electron repulsion
• Shapes include linear, bent, trigonal planar, tetrahedral, etc.

Properties of Covalent, Ionic, and Metallic Compounds

• Covalent compounds: low melting/boiling points, poor electrical conductivity
• Ionic compounds: high melting/boiling points, good electrical conductivity in liquid or aqueous form
• Metallic compounds: malleable, ductile, good electrical and thermal conductivity

Intermolecular Forces

• Attractive forces between molecules (not bonds), influence properties like boiling point, solubility

Alpha, Beta, Gamma Decay

• Radioactive decay processes (alpha, beta, gamma) involve unstable nuclei emitting particles
• Alpha: helium nucleus, Beta: electron/positron, Gamma: high-energy electromagnetic radiation.

Balancing Nuclear Equations

• Balancing nuclear equations ensures conservation of mass and charge during radioactive decay

Fission vs. Fusion Reactions

• Fission: splitting a heavy nucleus into lighter nuclei (e.g., nuclear power plants)
• Fusion: combining light nuclei into a heavier nucleus (e.g., stars)

Explore the history and organization of the periodic table through this quiz. Learn about the contributions of key scientists and differentiate between physical and chemical properties. Understand the distinctions between pure substances and mixtures, as well as the significance of grouping elements.