Atomic Structure Notes

Atomic Models

  • John Dalton (1803): Solid sphere model.
  • J.J. Thomson (1897): Plum pudding model - A ball of positive charge with electrons spread within it.
  • Ernest Rutherford (1909): Positively charged nucleus surrounded by electrons.
  • Niels Bohr (1913): Nucleus with electrons in shells and energy levels.

Key Terms

  • Atom: Smallest particle of matter, with electrons orbiting a nucleus of protons and neutrons.
  • Electrically Neutral: Equal number of protons (positive) and electrons (negative).
  • Element: Pure substance of one type of atom.
  • Matter: Particles making up physical substances.
  • Molecule: Two or more atoms chemically bonded.
  • Nucleus: Central part of an atom with protons and neutrons.

Matter

  • Takes up space and has mass.
  • Divided into pure and impure substances.
    • Pure substances: Elements and compounds.
      • Elements: One type of atom (e.g., gold, nitrogen).
      • Compounds: Two or more types of atoms chemically joined (e.g., salt, carbon dioxide).
    • Impure substances: Mixtures (e.g., air, milk, salt water).

Atomic Structure

  • All matter is made of atoms, the basic building blocks.
  • Over 90 naturally occurring elements exist.
  • Atoms bond to form molecules (e.g., glucose: 6 carbon, 12 hydrogen, 6 oxygen atoms). Identical atoms can bond (e.g., O2O_2).
  • Atoms are electrically neutral, containing:
    • Protons: Positive charge, in the nucleus, relative weight of 1.
    • Neutrons: No charge, in the nucleus, relative weight of 1.
    • Electrons: Negative charge, very small relative weight, located in shells/energy levels. First shell holds 2 electrons, second and third hold 8. Inner shells fill first.