Atomic Theory and Chemical Laws PDF

Atomic Theory and Chemical Laws Historical Overview 500 B.C.: Maharishi Kanad formulated the concept of indivisible particles called 'parmanu'. Ancient Greece: Philosophers Democritus and Leucippus referred to these particles as atoms. Antoine L. Lavoisier: Established foun...

Atomic Theory and Chemical Laws Historical Overview 500 B.C.: Maharishi Kanad formulated the concept of indivisible particles called 'parmanu'. Ancient Greece: Philosophers Democritus and Leucippus referred to these particles as atoms. Antoine L. Lavoisier: Established foundational laws for chemical combination, crucial for modern chemical sciences. Atoms and Atomic Theory Atoms are the building blocks of all matter, participating in chemical reactions. Atoms are extremely small, not visible with powerful microscopes. Dalton’s Atomic Theory All Matter: Composed of tiny particles called atoms. Indivisibility: Atoms can't be created or destroyed in chemical reactions. John Dalton: First to use symbols for elements. Limitations: Dalton's theory had shortcomings in explaining isobars, complex compounds, and allotropes. Laws of Chemical Combination Law of Conservation of Mass During a reaction, the mass of reactants equals the mass of products. Demonstrates that mass is neither created nor destroyed. Law of Constant Proportions Elements in a pure compound are always present in the same mass ratio. Example: Water (HO) consistently shows a hydrogen to oxygen mass ratio of 1:8. Atomic Mass Concept: Mass of an atom expressed in atomic mass units (u). IUPAC: Standardizes the term and its applications. 1 atomic mass unit (u) = 1/12 mass of a carbon-12 atom. Examples: Hydrogen atom: 1.673 × 10²⁴ grams or 1 u. Ions and Molecules Ions Cations: Positively charged ions (e.g., Na, Ca²). Anions: Negatively charged ions (e.g., Cl, SO²). Molecules Composed of atoms chemically bonded together. Exhibit properties of the substance. Monoatomic, Diatomic, Triatomic, Polyatomic categories based on atomicity. Chemical Formulae and Molecular Mass Chemical Formulae Symbolic representation demonstrating the composition of a compound. Rules: Balance valencies/charges. Metal symbols precede non-metal symbols. Polyatomic ions enclosed in brackets. Molecular Mass Sum of atomic masses of all atoms in a molecule. Example: HO molecular mass = 2 (Hydrogen) + 16 (Oxygen) = 18 u. Combining Atoms and Valency Atoms combine to achieve noble gas configuration via electron share, loss, or gain. Valency: An element’s combining capacity, reflecting electrons involved in bond formation. E.g., Sodium (Na) has a valency of 1.