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Transcript
Ch. 3: “Atoms and the Periodic Table” Section 3.1: “Atomic Structure” Objectives 1. 2. 3. Explain Dalton’s atomic theory, and describe why it was more successful than Democritus’s theory. State the charge, mass, and location of each part of an atom according to the modern model of the atom. Compare and contrast Bohr’s model with the modern model of an atom. Dalton’s Theory Every element is made of tiny, unique particles called atoms that cannot be subdivided. 2. Atoms of the same element are exactly alike. 3. Atoms of different elements can join to form molecules. Dalton’s theory was widely accepted because, unlike Democritus’s theory, there was evidence to support it. 1. Parts of an Atom proton (p+) = a positively charged subatomic particle in the nucleus of an atom (mass = 0.00000000000000000000000000167 kg) neutron (n◦) = a neutral subatomic particle in the nucleus of an atom (mass = 0.00000000000000000000000000167 kg) nucleus = the center of an atom; made up of protons and neutrons electron (e-) = a tiny negatively charged subatomic particle moving around the outside of the nucleus (mass = 0.000000000000000000000000000000911 kg) The Bohr Model vs the Modern Atomic Theory In both theories, electrons orbit the nucleus and each electron has an energy level associated with its location. In Bohr’s model of the atom, electrons were thought to orbit the nucleus in set paths, much like planets orbiting the sun. In the modern atomic theory, the region in an atom where electrons are likely to be found is called an orbital. But, the exact location of an electron cannot be determined according to this model. Electron Configuration The higher the energy level, the farther from the nucleus the electrons tend to be, and the more energy they have. Rules for filling energy levels: The first electrons enter the K shell, up to a maximum of 2. The next electrons enter the L shell, up to a maximum of 8. The next electrons enter the M shell, up to a maximum of 18, but are stable with 8. Electron Configuration Electron Configuration Valence: Whichever shell is currently most outward is the valence shell, even if it only has one electron. Valence electrons are those electrons that an atom uses in forming a bond with another atom. Generally, these electrons are found in the outermost shell of an element. How many valence electrons are in the first 18 elements?