chemistry chapter 2

COMPONENTS OF MATTER

  • Element: Cannot be separated into simpler substances.

  • Compound: Composed of two or more elements, chemically united in fixed proportions.

  • Mixture: Physical intermingling of substances, variable composition; can be separated physically.

    • Heterogeneous Mixtures: Non-uniform composition (e.g., raisin bran).

    • Homogeneous Mixtures: Uniform composition (e.g., salt water, solutions).

OBSERVATIONS LEADING TO ATOMIC THEORY

  • Democritus: Proposed existence of atoms; rejected for centuries until the 19th century.

  • Mass Conservation: Total mass remains unchanged in chemical reactions.

  • Definite Composition: Chemical compounds have the same relative mass ratio of elements.

  • Multiple Proportions: Different compounds from the same elements show mass ratios of small whole numbers.

DALTON'S ATOMIC THEORY

  1. Matter consists of atoms; tiny indivisible particles.

  2. Atoms of one element cannot convert to another.

  3. Atoms of an element are identical in mass and properties.

  4. Compounds result from combining specific ratios of atoms from different elements.

STRUCTURE OF THE ATOM

  • Evidence of Electrons: Cathode rays are deflected by electric/magnetic fields, implying they are negatively charged particles.

  • Electron Mass: Approximately 9.109imes10−289.109 imes 10^{-28} g; negatively charged at −1.602imes10−19-1.602 imes 10^{-19} C.

  • Atomic Nucleus: Contains protons and neutrons; protons have a charge of +1.602imes10−19+1.602 imes 10^{-19} C, neutrons are neutral.

ATOMIC NUMBER AND ISOTOPES

  • Atomic Number (Z): Number of protons in the nucleus.

  • Mass Number (A): Total of protons and neutrons.

  • Isotopes: Atoms with the same number of protons but different neutrons.

  • Notation: A Z X (e.g., for sulfur, 1633S^{33}_{16}S has 16 protons, 17 neutrons).

AVERAGE ATOMIC MASSES

  • Average atomic masses account for isotopic abundance; not all elements have near-integer values.

  • Example: Evaluate silicon isotopes to illustrate the calculation of average atomic mass.

PERIODIC TABLE STRUCTURE

  • Arranged by atomic number; elements in columns (families) share properties.

  • Key families: Alkali metals, Alkaline earth metals, Chalcogens, Halogens, Noble gases.

BONDING SCHEMES

  • Ionic Bonding: Electron transfer from metals to nonmetals forms charged ions.

  • Covalent Bonding: Atoms share electrons; forms molecules (e.g., H2O, C6H12O6).

NAMING COMPOUNDS

  • Ionic: Name cation + anion (e.g., NaCl = sodium chloride).

  • Covalent: Prefixes indicate number of atoms (e.g., CO2 = carbon dioxide).

  • Acids: Based on anion (binary acids; -ide to -ic with 'hydro-', oxoacids by oxoanions).

MOLECULAR MASSES

  • Calculate molecular mass using atomic masses of constituent atoms.

  • Example: Vitamin C (C6H8O6): Sum of atomic masses yields total molecular mass.

OBSERVATIONS LEADING TO ATOMIC THEORY

  • Democritus: Proposed existence of atoms; rejected for centuries until the 19th century.

  • Mass Conservation: Total mass remains unchanged in chemical reactions.

  • Definite Composition: Chemical compounds have the same relative mass ratio of elements.

  • Multiple Proportions: Different compounds from the same elements show mass ratios of small whole numbers.

STRUCTURE OF THE ATOM

  • Cathode Ray Experiment (J.J. Thomson): Cathode rays are deflected by electric/magnetic fields, implying they are negatively charged particles (electrons).

  • Oil Drop Experiment (Robert Millikan): Determined the precise charge of an electron at −1.602×10−19-1.602 \times 10^{-19} C, leading to the calculation of its mass.

  • Gold Foil Experiment (Ernest Rutherford): Led to the discovery of the atomic nucleus; most alpha particles passed through, but some were deflected at large angles, indicating a small, dense, positively charged core.

  • Electron Mass: Approximately 9.109×10−289.109 \times 10^{-28} g; negatively charged at −1.602×10−19-1.602 \times 10^{-19} C.

  • Atomic Nucleus: Contains protons and neutrons; protons have a charge of +1.602×10−19+1.602 \times 10^{-19} C, neutrons are neutral.

The overall atom is neutral, as the number of electrons equals the number of protons, balancing the electric charge.