Law of the Conservation of Mass – when chemical reactions occur, the atoms are only rearranged and there is no difference in mass following a chemical reaction.Conclusions made based on his experiments and postulates:.He made no prediction about the construction of atoms believing them to be solid spheres.When elements react, their atoms sometimes combine in more than one simple whole, number ratio. When elements react, their atoms combine in simple, whole number ratios. Elements are characterized by the mass of their atoms. Atoms are indestructible and unchangeable. All matter consists of tiny particles called atoms Contributions – Five Postulates of Atomic Theory.Experimented extensively with multiple gases and gaseous compounds.1932: James Chadwick – Discovers neutrons.1913: Niels Bohr – Theorizes structure of the electron cloud with energy levels and planetary orbits of electrons.1911: Ernest Rutherford – Discovers positively charged nucleus.1908 Robert Millikan – Determines the charge of the electron.Thomson – Discovery of the negatively charged electron and the mass to charge ratio of the electron 1803: John Dalton – Postulates of Atomic Theory.1605: Francis Bacon – published the scientific method.Democritus – ancient Greek philosopher that originally stated all matter consists of atoms.Major Contributors to Understanding Atomic Structure.Theory - An explanation supported by many experiments is still subject to new experimental data, can be modified, and is considered valid if it can be used to make predictions that are proven true.Subatomic particles - The three kinds of particles that make up atoms: protons, neutrons, and electrons.Mass number - The total number of protons and neutrons in a nucleus.The atomic number is written as a subscript on the left of the element symbol, the mass number is written as a superscript on the left of the element symbol Isotope notation - Subscripts and superscripts can be added to an element’s symbol to specify a particular isotope of the element and provide other important information.Isotope -Atoms of the same element with different numbers of neutrons.Dalton’s Postulates - States that matter is composed of extremely small particles called atoms atoms are invisible and indestructable atoms of a given element are identical in size, mass, and chemical properties atoms of a specific element are different from those of another element different atoms combine in simple whole-number ratios to form compounds in a chemical reaction, atoms are separated, combined, or rearranged. ![]()
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