Unit 3 chem

Early Ideas about matter

Democritus views on matter:

  • Matter is composed of atoms

  • Atoms are solid, homogeneous, indestructible, and indivisible

  • Atoms move through empty space

  • Different kinds of atoms have different sizes, shapes, and movement

Aristotles ideas

  • Empty space cannot exist

  • Matter was composed of earth, fire, water, and air

  • Denied the existence of atoms

How were they different?

  • Aristotle disagreed with Democritus and said atoms or empty space did not exist

  • Rejected D. ideas mainly because it did not agree with the ideas of his nature 

  • The public sided with A. because of his popularity, and D.’s ideas, although ahead of his time, were not believed

Daltons atomic theory

  • All matter is composed of extremely small particles called atoms

  • All atoms of a given element are identical in size, mass, and chemical propertes

    • Atoms of one element are different from atoms of another element

  • Atoms cannot be created, divided into smaller particles, or destroyed

  • Different atoms combine with simple whole-number ratios to form compounds

  • In a chemical reaction, atoms are separated, combined, or rearranged

  • The conservation of mass in chemical reactions is the result of the rearrangement of atoms during the reaction

    • They are not created or destroyed

Defining the Atom

J.J. Thomson(1897)

  • Cathode ray tubes-> discovered electron

  • Determined charge-to-mass ration of electron

  • Atoms can be broken down-> subatomic particles

  • Plum pudding model

    "Plum pudding Model"

Robert Millikan(1909)

  • Determined the mass AND charge of the electron using “oil-drop experiment”

Earnest Rutherford(1911)

  • Discovered that the atom is mostly empty space-electrons move

  • Concluded that all atoms positive charge + most of the mass is in the nucleus

  • Nucleur model

    "nucleur model"

How atoms differ

  • Number of protons (or electrons) in an atom -> identifies as an aton of a particular element

    • Called atomic number

  • Periodic table organization

    • Left-to-right

    • Top-2-bottom

  • ISOTOPES=same number protons and electrons, different number neutrons

  • MASS NUMBER= sum of protons and neutrons

Atomic mass v mass number

  •  ATOMIC MASS= the weighted average mass of the isotopes of that element

    Abundance in decimal form!