Atomic Structure, Periodicity, and Matter: Review

Review

• The development of the structure of the atom spanned centuries beginning with the Greek philosopher Democritus, with major contributions from John Dalton, Michael Faraday, William Crookes, Wilhelm Roentgen, Henri Becquerel, Marie and Pierre Curie, Ernest Rutherford, and many others.
• A number of scientists attempted to describe the atom by proposing models. Significant among those were J.J. Thomson, Neils Bohr, Erwin Schrödinger, and James Chadwick. Their efforts have resulted in today’s quantum mechanical model of the atom.
• The nucleus of the atom is composed of positive protons and neutral neutrons therefore giving the nucleus its positive charge.
• The electrons are negative particles that surround the nucleus in energy levels. Within the principal energy levels are sublevels classified as s, p, d, or f.
• As elements were rapidly being discovered, chemists such as Johann Dobereiner, John Newlands, and others began to see relationships among them.
• From the pioneer work of the early chemists, Dimitri Mendeleev is credited with developing the periodic table, an invaluable tool to all chemists. The periodic table shows characteristics shared within groups of elements as well as trends of properties down and across the table.
• Planck introduced the energy quantum to explain black body radiation.
• Einstein explained the photoelectric effect by proposing that a light wave consists of discrete photons.
• Compton demonstrated the particle nature of light waves and de Broglie proposed that matter has wave properties.
• Spectra of gaseous atoms consist of discrete lines. Lines in the hydrogen spectrum are described by a simple formula.
• The arrangement of electrons in atoms is closely related to the chemical properties of the elements and to the structure of the periodic table.
• The Pauli exclusion principle specifies that each electron in an atom must have a unique set of four quantum numbers.
• The aufbau (“building up”) rule assumes that as electrons are added to an atom they fill the lowest energy orbitals first.
• The strong nuclear force binds protons and neutrons together in the nucleus. When protons and neutrons combine to form a nucleus, mass is converted into energy.
• Nuclei of light elements can fuse to form heavier nuclei.
• Nuclei of heavy elements can split apart to form lighter nuclei.
• If the mass of products for a nuclear reaction is greater than the mass of reactants, the reaction is not possible; if the mass of products is less than the mass of reactants, the reaction may occur.
• Einstein’s relationship between mass and energy, ∆E = ∆mc², can be used to predict the amount of energy produced in a nuclear reaction.
• The essential difference between a conventional power generating plant and a nuclear one is the source of heat to make steam. Heat to generate steam comes from burning gas, oil, or coal for the former, and from nuclear energy for the latter.

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