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Chapter 17 Sections 1 and 2 Atomic Components • Atom– smallest piece of matter that still retains the property of the element • Nucleus—the small, positively charged core of an atom where the protons and neutrons reside • Protons—positively charged particles • Neutrons—neutrally charged particles • Electrons—negatively charged particles Quarks • Small particles that make up protons and neutrons • Scientists theorize that an arrangement of three quarks held together with the strong nuclear force produces a proton. Another arrangement of three would produce a neutron. • To find quarks, scientists accelerate charged particles to tremendous speeds and then force them to collide with protons. This causes the proton to break into smaller pieces known a quarks. • Scientists use inference to identify the subatomic particles and to reveal information about each particle's inner structure. Models • There have been 5 accepted models of the atom. • Dalton/ Democritus • Thomson • Rutherfod • Bohr • Electron Cloud Dalton’s Model • Dalton’s model was that of a solid sphere Thomson’s Model • Atoms contain small, negatively charted particles • He said these electrons (pictured in blue) were evenly embedded throughout a positively charged sphere, much like chocolate chips in a ball of cookie dough. Rutherford’s Model • Almost all the mass of an atom—and all it’s positive charges—were concentrated in a central atomic nucleus surrounded by electrons. Bohr’s Model • Electrons traveled in fixed orbits around the atom’s nucleus. Chadwick • He didn’t create a new model just expanded what his teacher Rutherford did. • He concluded that the nucleus contained positive protons and neutral neutrons. • This worked with Bohr’s model. Modern Model • Electrons do NOT follow a fixed orbit, but tend to occur more frequently in certain areas around the nucleus at any given time Atomic number and mass • Atomic number is the number of protons in an atom. • By looking at the atomic number you can figure out how many neutrons there are as well. Neutrons equal the protons unless it is an isotope • An isotope is an atom that has a different number of neutrons. • Atomic mass or mass number is the sum of the number of protons and neutrons in the nucleus. • IF you know the mass number you can calculate the number of neutrons the equation is: • Number of neutrons = mass number – atomic number