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Atoms Chapter 4 Atomic Theory & Structure Definition of the Atom • Remember, Democritis defined “atomos” as the SMALLEST, INDIVISIBLE part of matter that still had physical and chemical properties? • Democritus was wrong! Atoms CAN BE DIVIDED INTO SMALLER PARTS!!! Modern Definition of the Atom • John Dalton • Atomic Theory • 1. Atoms are the smallest part of matter that RETAINS PROPERTIES. • 2. All atoms of an element are the same. • 3. Atoms of different elements can join to form compounds. Parts of an Atom • Nucleus - inside • Made of – Protons (positive) – Neutrons (neutral) • Electron Cloud - outside • Made of – Electrons (negative) • Same number of protons and electrons! (Same number of positives as negatives!!) If the protons & electrons are the same in every atom the same element…. • …then what is the charge of a typical atom? • 2 protons & 2 electrons • +2 + (-2) = 0 NEUTRAL!! • Atoms are typically neutral or they have no charge! Orbits in the Electron Cloud • Electrons orbit the nucleus in “rings” or energy levels. • Notice how the electrons orbit the nucleus in many different dimensions. Remember, the atom is 3D! The Nucleus is the Heaviest Part… • The Neutrons and Protons are VERY HEAVY!! – They are made of even smaller part called QUARKS. • The Electrons are so small they are almost WEIGHTLESS!! • The “Rings” don’t actually exist, they are just drawn in the picture to illustrate the path of the orbits. Energy Levels or “Rings” • For our purposes, there are four rings around the nucleus. • The closest ring holds 2 electrons. • The second ring holds 8 electrons. • The third ring holds 8 electrons. • The fourth ring holds 2 electrons. Review: STORYTIME!!! • Let’s hear a story about the …. ATOMS FAMILY!! http://youtu.be/Q9Pt6WZpTxU Something to Think About… • What is the difference between an atom and a cell? • Cells are the smallest LIVING things. Atoms are the smallest part of EVERYTHING and they are not alive!