Chem

Discovery of the Electron

  • The section title indicates the topic: Discovery of the Electron (e).
  • Becquerel’s work is mentioned in the context of discovering radioactivity: "Becq wered discovers Radio Selvity" (OCR error for Becquerel discovers radioactivity).
  • Types of radiation are hinted:
    • Alpha particles: positively charged ("+").
    • Beta particles: negatively charged and of lower mass ("low mass (-)").
  • The reference to alpha and beta suggests early characterization of radiation types associated with subatomic particles.

Moseley’s Atomic Numbers and the Periodic Table

  • Moseley’s Atomic Numbers are cited: "Mosely's Atomic Numbers".
  • Purpose: confirm Mendeleev’s ordering of the elements in his table.
  • Key idea: atomic number (Z) provides the fundamental ordering, supporting the periodic table arrangement.

Nuclear Model of the Atom: Rutherford, Chadwick, and Isotopes

  • Rutherford’s experiments lead to several conclusions about atomic structure:
    • The mass of the atom is contained in a small, dense nucleus (phrased as: “Mass of Atom is contained in a cercle us/nucleus”).
    • The nucleus contains protons and neutrons; the rest of the atom is mostly empty space where the electrons reside.
  • Chadwick (1937) is credited with discovering the neutron, establishing the neutron as a neutral nuclear constituent.
  • Isotopes:
    • Atoms of the same element can have different masses ("multiple atoms for an Element, with different Messes = isotopes").
    • Isotopes differ in neutron number while the number of protons (and thus the atomic number Z) remains the same.
  • Proton and neutron roles:
    • Protons carry positive charge; atomic number Z equals the number of protons in the nucleus.
    • Neutrons are neutral and contribute to the mass number.
  • Neutral atoms:
    • In a neutral atom, the total charge balances, so the number of electrons equals the number of protons (Z).
  • Mass number and composition:
    • Mass number A equals the sum of protons and neutrons: A=Z+NA = Z + N where N is the number of neutrons.
  • Summary relationships:
    • Atomic number Z = number of protons.
    • Neutrons N = A − Z.
    • Isotopes have the same Z but different N and therefore different A.
    • A neutral atom has Z protons, Z electrons, and N neutrons in the nucleus (for a given isotope).

Nuclear Composition and Notation

  • Key definitions:
    • Z = atomic (proton) number.
    • N = number of neutrons.
    • A = mass number = Z + N.
  • Important implication: isotopes differ in N (and thus A) but share Z.
  • Example form (notation):
    • Element X with Z protons and N neutrons has mass number A=Z+NA = Z + N.
    • Neutral atom of this isotope has Z electrons.

Converting Units in Calculations

  • Goal: perform unit conversions accurately to obtain a desired unit.
  • Step 1: Understand the goal of the unit conversion.
  • Step 2: Identify the given quantity and the desired quantity (units).
  • Step 3: Find appropriate conversion factors that relate the given units to the desired units.
  • Step 4: Set up the calculation using dimensional analysis.
  • Dimensional analysis (the method) explained:
    • Convert factors are used to change units of a quantity.
    • Start with the given quantity and multiply by conversion factors so that unwanted units cancel.
    • Each conversion factor is arranged so that the unit you want in the numerator or denominator cancels the unwanted unit.
    • The factor in the numerator should contain the unit you want; the factor in the denominator contains the unit you are canceling.
  • General framework (symbolic):
    • Let the given quantity be a value with units Ug, and the desired unit be Ud.
    • Use a chain of conversion factors to move from Ug to Ud:
    • $$Q{ ext{desired}} = Q{ ext{given}} imes rac{U1}{U2} imes rac{U3}{U4} imes rac{U5}{U6} imes \