CHE 110 Chapter Notes - Chapter 2: Robert Andrews Millikan, Nucleon, Unified Atomic Mass Unit
Document Summary
All matter is composed of small particles - atoms. Thought atoms were indivisible - did not understand subatomic particles. Retains chemical and physical identity during chemical reaction. Elements - all atoms of the same element are exactly alike. Compounds - atoms of 2+ elements chemicals combine in xed proportions. J. j thompson - cathode-ray tubes & discovery of the electron (1897) Neutron nuclear particle with mass almost identical to proton mass, no electrical charge. Atomic diameter 10^-10m (100pm) nucleus diameter 10^-15m (10^-3pm) Mass: 9. 10938 10-28 g or 5. 534 x 10-3 amu. Sum of all protons and neutrons in the nucleus of an atom. All atoms of an element have the same atomic number. Same number of protons (de nes the atom), different number of neutrons. Expressed in atomic mass units (amu) (sum of isotope mass) * (isotope abundance) Organized the elements based on the known atomic masses. Highlighted the regular repetition of the propertied of the elements.
