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Chapter 5 The ATOM • Democritus (400 BC) reasoned that all things were made up of indivisible particles: ATOMS • Dalton (1766-1844) performed experiments – Atomic Theory • All elements are composed of tiny indivisible particles called ATOMS • Atoms of the same element are identical, but different from other elements • Atoms of different elements can physically or chemically combine in whole number ratios • Chemical reactions occur when atoms are joined, separated, or rearranged. But atoms of one element ae never changed into atoms of another element. • Atoms are really, really small – A copper coin has about 2.4 x 10^22 atoms • 24,000,000,000,000,000,000,000 atoms • Atomic Structure Electrons (JJ Thompson 1897) -negative charge -Millikan calculated the weight and charge of the electron in 1916 Protons and Neutrons -Protons (Goldstein 1886)are Positive and about 1840 times the size of an electron -Neutrons (Chadwick 1932) are Neutral and have about the same weight as a proton Rutherford 1911: Most of an atom is empty space, positive charge centered in the nucleus Atomic Number – On the periodic table – Tells number of protons and electrons Mass Number -On the periodic table -unit = AMU (atomic mass units) -Number of protons + neutrons -to find the number of neutrons, MASS NUMBER – ATOMIC NUMBER Isotopes • Atoms that have the same number of protons, but different numbers of neutrons are called ISOTOPES • Will have same ATOMIC NUMBER, but different MASS NUMBER • Example: Carbon-12 and Carbon-14 • Both have an atomic number of 6, but the mass numbers are different Atomic Mass • Most elements occur as a mixture of two or more isotopes. • The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element Your Project You are going to write a book to explain early atomic theory and structure to elementary children. Part one: Atomic Theory You must include: Dalton’s Atomic Theory, JJ Thompson, Rutherford, and Bohr. Part Two: Parts of the periodic table You must include: Where to find atomic symbol, mass, and number How to calculate the number of protons, neutrons, and electrons Grading • I am grading this for completion and ‘appearance’ • For full credit, you MUST include all of the required pieces, the book must be neat and organized, and the information must be correct and clearly stated. • Opportunity for bonus: Go above and beyond? You’ll earn points on your midterm!
